U.S. patent application number 10/888092 was filed with the patent office on 2005-03-10 for skeletal implant.
This patent application is currently assigned to Fred ZACOUTO. Invention is credited to Caballero, Efren Vigil, Canal, Jose Angel Alvarez, Zacouto, Fred.
Application Number | 20050055025 10/888092 |
Document ID | / |
Family ID | 27446978 |
Filed Date | 2005-03-10 |
United States Patent
Application |
20050055025 |
Kind Code |
A1 |
Zacouto, Fred ; et
al. |
March 10, 2005 |
Skeletal implant
Abstract
Skeletal implant of the type to be used to connect at least two
elements of a skeleton. The skeletal implant includes a first part
adapted to be connected to at least one of the at least two
elements of the skeleton. A second part is adapted to be connected
to another of the at least two elements of the skeleton. A variable
volume element is adapted to move the first and second parts with
respect to each other. A high-pressure chamber supplies fluid to
the variable volume element. A low-pressure chamber receives fluid
from the variable volume element. A recharging variable volume
element is adapted to communicate with the high-pressure chamber
and the low-pressure chamber. The recharging variable volume
element is responsive to displacements of corporal parts of a user
and recharges the high-pressure chamber with fluid. This Abstract
is not intended to define the invention disclosed in the
specification, nor intended to limit the scope of the invention in
any way.
Inventors: |
Zacouto, Fred; (Paris,
FR) ; Caballero, Efren Vigil; (Gijon, ES) ;
Canal, Jose Angel Alvarez; (La Feiguera, ES) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
Fred ZACOUTO
Paris
FR
|
Family ID: |
27446978 |
Appl. No.: |
10/888092 |
Filed: |
July 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10888092 |
Jul 12, 2004 |
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10040429 |
Jan 9, 2002 |
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6835207 |
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10040429 |
Jan 9, 2002 |
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09200855 |
Nov 30, 1998 |
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09200855 |
Nov 30, 1998 |
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08897673 |
Jul 21, 1997 |
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Current U.S.
Class: |
623/17.12 ;
623/16.11; 623/22.14; 623/23.17 |
Current CPC
Class: |
A61B 17/7031 20130101;
A61F 2/30742 20130101; A61F 2002/2825 20130101; A61F 2002/30462
20130101; A61F 2002/30354 20130101; A61B 17/68 20130101; A61B
2017/00017 20130101; A61B 2017/00539 20130101; A61F 2002/448
20130101; A61B 17/7059 20130101; A61F 2220/0025 20130101; A61F
2002/30546 20130101; A61F 2002/30884 20130101; A61F 2220/0075
20130101; A61F 2250/0012 20130101; A61F 2002/365 20130101; A61F
2002/30242 20130101; A61B 17/74 20130101; A61F 2/28 20130101; A61F
2002/30563 20130101; A61F 2002/30581 20130101; A61F 2002/30589
20130101; A61F 2/441 20130101; A61F 2250/0013 20130101; A61F
2002/30069 20130101; A61F 2002/30225 20130101; A61F 2002/30593
20130101; A61F 2002/3647 20130101; A61F 2002/30548 20130101; A61F
2230/0069 20130101; A61F 2220/0033 20130101; A61F 2002/30975
20130101; A61F 2002/286 20130101; A61B 17/7026 20130101; A61B
17/6491 20130101; A61F 2/367 20130101; A61F 2002/30235 20130101;
A61F 2002/30841 20130101; A61F 2002/48 20130101; A61F 2002/30372
20130101; A61F 2/44 20130101; A61F 2002/30586 20130101; A61F
2230/0071 20130101; A61F 2002/3055 20130101; A61B 17/645 20130101;
A61F 2002/30578 20130101; A61F 2250/0002 20130101; A61B 17/70
20130101; A61F 2002/30405 20130101; A61B 2017/00022 20130101; A61F
2/3609 20130101; A61B 2017/606 20130101; A61F 2/4425 20130101; A61F
2002/3037 20130101; A61F 2/442 20130101; A61F 2002/3067 20130101;
A61B 17/7001 20130101 |
Class at
Publication: |
606/072 ;
623/016.11 |
International
Class: |
A61B 017/56 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 22, 1996 |
FR |
FR 9609157 |
Apr 30, 1998 |
FR |
FR 9805549 |
Claims
What is claimed:
1. A skeletal implant of the type to be used to connect at least
two elements of a skeleton, the skeletal implant comprising: a
first part adapted to be connected to at least one of the at least
two elements of the skeleton; a second part adapted to be connected
to another of the at least two elements of the skeleton; a variable
volume element adapted to move the first and second parts with
respect to each other; a high-pressure chamber supplying fluid to
the variable volume element; and a low-pressure chamber receiving
fluid from the variable volume element; and a recharging variable
volume element adapted to communicate with the high-pressure
chamber and the low-pressure chamber, wherein the recharging
variable volume element is responsive to displacements of corporal
parts of a user and recharges the high-pressure chamber with
fluid.
2. The implant of claim 1, further comprising another variable
volume element disposed in the high-pressure chamber.
3. The implant of claim 1, further comprising a high-pressure valve
allowing fluid to enter the variable volume element from the
high-pressure chamber.
4. The implant of claim 1, wherein the low-pressure chamber
comprises a deformable impermeable sleeve.
5. The implant of claim 4, further comprising a low-pressure valve
allowing fluid to exit the variable volume element and enter the
low-pressure chamber.
6. The implant of claim 1, further comprising a third part having
one end coupled to the first part and another end disposed between
the variable volume element and the second part.
7. The implant of claim 1, wherein the variable volume element
comprises one end coupled to the first part and another end coupled
to a third part.
8. The implant of claim 1, further comprising a third part having a
threaded opening which engages a threaded portion of the second
part.
9. The implant of claim 1, wherein the recharging variable volume
element comprises one end that is coupled to a third part and
another end that is coupled to the first part.
10. The implant of claim 9, wherein the second part is rotatably
coupled to at least one of the variable volume element and the
third part.
11. The implant of claim 1, further comprising a sealed bellows
disposed in the high-pressure chamber.
12. The implant of claim 1, wherein the recharging variable volume
element comprises a metal bellows having one end coupled to the
first part and another end coupled to a third part.
13. The implant of claim 1, further comprising a sleeve defining a
variable volume of the low-pressure chamber.
14. The implant of claim 1, further comprising a high-pressure
conduit connecting the variable volume element to the high-pressure
chamber.
15. The implant of claim 1, wherein the variable volume element
comprises a metal bellows.
16. The implant of claim 1, wherein at least one of the first part
and the second part comprises an opening which is adapted to
receive a connecting member, whereby the connecting member connects
the first or second part to one of the at least two elements of the
skeleton.
17. A skeletal implant of the type to be used to connect at least
two elements of a skeleton, the skeletal implant comprising: a
first part adapted to be connected to at least one of the at least
two elements of the skeleton; a second part adapted to be connected
to another of the at least two elements of the skeleton; a variable
volume element adapted to move the first and second parts with
respect to each other; a high-pressure chamber supplying fluid to
the variable volume element; and a low-pressure chamber receiving
fluid from the variable volume element; and a recharging variable
volume element adapted to communicate with the high-pressure
chamber and the low-pressure chamber, wherein the implant is
adapted to provide a damping effect with an adjustable coefficient
of resistance.
18. A skeletal implant of the type to be used to connect at least
two elements of a skeleton, the skeletal implant comprising: a
first part adapted to be connected to at least one of the at least
two elements of the skeleton; a second part adapted to be connected
to another of the at least two elements of the skeleton; a variable
volume element having a first end coupled to the first part and a
second end, the variable volume element being adapted to move the
first and second parts away from each other; a third part having a
first end coupled to the first part and a second end coupled to the
second end of the variable volume element; a high-pressure chamber
supplying fluid to the variable volume element; a low-pressure
chamber receiving fluid from the variable volume element; and a
recharging variable volume element responsive to displacements of
corporal parts of a user and recharging the high-pressure chamber
with fluid.
19. The implant of claim 18, wherein the recharging variable volume
element includes a first end coupled to the first end of the third
part and a second end coupled to the first part.
20. The implant of claim 19, wherein the recharging variable volume
element is adapted to communicate with at least one of the
high-pressure chamber and the low-pressure chamber.
21. The implant of claim 18, wherein the second part is rotatably
coupled to at least one of the variable volume element and the
third part.
22. The implant of claim 18, further comprising a high-pressure
valve allowing fluid to enter the variable volume element from the
high-pressure chamber.
23. The implant of claim 18, further comprising a low-pressure
valve allowing fluid to exit the variable volume element and enter
the low-pressure chamber.
24. The implant of claim 18, wherein at least one of the first part
and the second part comprises an opening which is adapted to
receive a connecting member, whereby the connecting member connects
the first or second part to one of the at least two elements of the
skeleton.
25. A skeletal implant of the type to be used to connect at least
two elements of a skeleton, the skeletal implant comprising: a
first part adapted to be connected to at least one of the at least
two elements of the skeleton; a second part adapted to be connected
to another of the at least two elements of the skeleton; a variable
volume element having a first end coupled to the first part and a
second end, the variable volume element being adapted to move the
first and second parts away from each other; a third part having a
first end coupled to the first part and a second end coupled to the
second end of the variable volume element; a high-pressure chamber
supplying fluid to the variable volume element; and a low-pressure
chamber receiving fluid from the variable volume element, wherein
the implant is adapted to provide a damping effect with an
adjustable coefficient of resistance.
Description
RELATED APPLICATION
[0001] The present application is a continuation of U.S.
application Ser. No. 10/040,029, filed Jan. 9, 2002, which is a
continuation of U.S. application Ser. No. 09/200,855, filed Nov.
30, 1998, the disclosures of each of these documents is expressly
incorporated by reference herein in their entireties. Application
Ser. No. 09/200,855 is a continuation-in-part of application Ser.
No. 08/897,673, filed on Jul. 21, 1997, now abandoned, the priority
of which is claimed under 35 USC 120 and the disclosure of which is
incorporated by reference thereto in its entirety. Further, the
present application claims priority under 35 U.S.C. .sctn. 119 of
French Patent Application No. 9609157 filed on Jul. 22, 1996 and
French Patent Application No. 9805549 filed on Apr. 30, 1998, the
disclosures of which are hereby incorporated by reference thereto
in their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a skeletal implant, and
more particularly to an implant of this type to be used for
connecting at least two elements of the skeleton, which implant is
embodied in at least two parts, each of which is capable of being
connected to one of these elements.
[0004] According to a first aspect of the invention, it relates to
a consolidating and/or connecting implant, and more particularly to
an implant of this type to be used to consolidate a connection
between two bone elements, of the type comprising a first part
designed to be attached to one of the elements and a second part
designed to be attached to the other element.
[0005] 2. Background and Material Information
[0006] There are known implants of this type that are capable of
being used, for example, in the case of a performance of a bone
graft or during the formation of a callus following a fracture. The
two ends of the implant, which are rigidly connected to one
another, for example because they are embodied in one piece, are
each attached, for example screwed, to a bone element located on
either side of the graft. When the graft has consolidated, the
implant can be removed.
[0007] However, there are numerous cases where the implant is left
in place. This is particularly the case when the implant is used to
replace a bone structure which is impossible to restore or to
construct.
[0008] In such cases, the rigidity of the implant, which is often
indispensable at the beginning of the implantation, during the
formation of the callus, later constitutes a drawback. In effect,
the bone structures no longer sustain sufficient mechanical stress.
Therefore, they do not reconstitute themselves in an optimal way,
this reconstitution being tied to a satisfactory stressing of the
bone, the disturbance of which has consequences which can result in
post-surgical pain that is very difficult to treat.
[0009] Moreover, when the implant is to be used to connect two bone
elements which are normally capable of moving relative to one
another, as in the case of a rachidian implant, this rigidity
results in a functional handicap in the patient in whom it is
implanted, and excessive stress on the neighboring joints.
SUMMARY OF THE INVENTION
[0010] The object of the invention is, among other things, to
eliminate these drawbacks.
[0011] According to a second aspect of the invention, it relates to
an articulated implant, and more particularly to an implant of this
type intended either to be intercalated between two bone elements
in relative motion, such as an artificial intervertebral disk, or
to replace a joint or an element of a joint, such as an artificial
head of the femur.
[0012] As regards the intercalated implant, it can be beneficial to
assist the adjacent bone structures and the ligaments during rapid,
or even violent movements. On the other hand, it may be preferable
to allow these structures and ligaments to work during slow
movements or simple static loads in order to prevent atrophy or
weakening.
[0013] As regards the articulated implant itself, a completely
rigid structure fully transmits the shocks and vibrations to the
other element of the joint, resulting in a risk of dystrophy or
rupture of this other element.
[0014] Also, once a surgical skeleton implant is implanted no
modification can be made to adapt the implant to the changing needs
of the patients.
[0015] Another object of the present invention is to eliminate
these drawbacks.
[0016] To this end, the subject of the invention is a skeletal
implant of the type to be used for connecting at least two elements
of the skeleton, which implant is embodied in at least two parts,
each of which is capable of being connected to one of these
elements, there parts being movable with respect to each other,
characterized in that it comprises between these two parts at least
one adjustable device responsive to non invasive control means,
said control means being preferably located on said implant, to
exert an adjustable force, for example a distraction or compression
force, between said parts, and/or to authorise an adjustable
displacement between said parts between a starting position and a
displaced position in which said parts should, at least
temporarily, be maintained, and/or to secure a damping effect with
an adjustable coefficient of resistance.
[0017] It is noted, first of all, that the adjustment can be
discrete as well as continuous, and for example, can include only
two positions of adjustment.
[0018] It is known that a shock-absorbing device is a device
generally comprising two chambers of variable volume filled with a
hydraulic fluid and connected by a calibrated opening. A device of
this type is intended to <<cushion >> the movements
between two elements, one of which is connected to a structure of
one of the chambers, the other being connected to an element in
which the calibrated opening is formed.
[0019] When the two elements move relative to one another, the
volumes of the two chambers vary in inverse proportion to one
another, the hydraulic fluid being laminated at the level of the
calibrated opening. The result is a force which opposes the
relative movement between the two elements which, as will be shown,
is proportional to the speed of this movement.
[0020] Used within the scope of the invention, a device of this
type applied to an implant of the consolidating and/or connecting
type has the advantage of allowing the bone structures to function,
and thus to develop, in a practically normal way at moderate
relative speeds between the bone elements connected by the implant,
particularly in the case of static stresses. On the other hand, the
greater the relative speeds, particularly in the case of voluntary
rapid movement or shock, that is, dynamic stresses, the greater the
portion of the stress absorbed by the implant.
[0021] The result is that the osteo-ligamentous structure, weakened
by the situation which justified the insertion of the implant, can
nevertheless function and thus reconstitute normally as long as the
stresses remain moderate. But the greater these stresses, the more
the natural structure is assisted by the implant.
[0022] Moreover, the coefficient of resistance being adjustable, it
is possible to reduce it progressively as the bone structure
reconstitutes. The latter can also sustain more and more dynamic
stresses until, eventually, it returns to normal functioning.
[0023] It is noted that it has already been suggested in the prior
art to endow prostheses with viscous and/or elastic means intended
to absorb shocks. Likewise, it is well known to provide, in certain
prostheses, regulating or adjusting means. However, no prosthesis
with a functional characteristic of viscous resistance has yet been
proposed wherein the coefficient of resistance would be adjustable.
This combination is essential in the primary function of the
invention, which is to allow a progressive reconstitution of the
bone structure and an optimal continuous adaptation to the state of
this structure.
[0024] When applied to an articulated implant, the invention also
makes it possible to give the articulation greater flexibility,
which, as in the prior art, allows it to absorb shocks, but in this
case also allows the neighboring bone structures and ligaments to
work.
[0025] Finally, the consequence of this shock-absorbing
characteristic is to protect the implant itself, as well as joints
located above and below the implant, from shocks.
[0026] In one particular embodiment, the implant comprises
removable means for locking the shock-absorbing device at a
predetermined length.
[0027] The implant according to the invention, in this embodiment,
can function during a first period in the traditional way, like a
rigid implant. This phase of functioning is for example that of the
formation of the callus in the case of a graft. During a second
period, the locking means are removed and the implant functions
according to the invention, exerting between the elements to which
it is connected a force which is proportional to their relative
speed and is therefore a function of the stresses exerted in the
graft.
[0028] In another particular embodiment, the implant comprises
means for limiting the travel of the shock-absorbing device.
[0029] This has the advantage of rendering the implant rigid in the
case where the stresses reach a certain limit. Thus, there is no
risk of reaching the rupture stress point.
[0030] Advantageously, these means for limiting the travel are
adjustable.
[0031] The travel of the shock-absorbing device can therefore be
adapted to the patient and possibly increased progressively as the
graft strengthens.
[0032] An implant according to the invention can be embodied in the
form of an elongated element such as a screw, or a pin such as a
coxofemoral prosthesis pin, or even the neck, the body or the head
of a femoral prosthesis, comprising two end parts connected by a
flexible middle part, the middle part comprising two chambers
filled with hydraulic fluid, disposed on either side of a neutral
axis and designed such that one of them increases in volume while
the other decreases in volume when the implant flexes, these
chambers being linked by at least one calibrated conduit.
[0033] This embodiment can be used to connect the two parts of a
fractured bone to one another, for example the femur at the level
of the neck or the diaphysis. The screw is positioned so that its
middle part is located at the point of the fracture, with its
neutral axis disposed as near as possible to the plane of maximum
flexion under stress. Thus, after the formation of the callus, the
implant will continue to assist it during sudden efforts, the
hydraulic fluid being forced from the chamber whose volume
decreases to the chamber whose volume increases, through the
calibrated opening. On the other hand, the callus will sustain the
static stresses on its own.
[0034] More particularly, these end parts can be connected by an
elastic wall delimiting these chambers with a peripheral
bellows.
[0035] As will be seen below, it is often advantageous to add an
elastic component to the viscous component of the implant's
behavior.
[0036] The calibrated conduit can be embodied in the form of
borings in at least one of the end parts.
[0037] This produces a very compact embodiment that is well suited
to the embodiments of the implant in the form of a screw.
[0038] Advantageously, a valve is provided on the calibrated
conduit.
[0039] This valve can initially be closed during the formation of
the callus. Thus the implant is perfectly rigid and behaves like a
classic screw. The valve is then opened so that the implant
functions according to the invention, with its shock-absorbing
function. A valve with a progressive opening also makes it possible
to provide the function for adjusting the coefficient of
resistance.
[0040] The control of the valve is preferably housed at the end of
the implant, nearest the skin.
[0041] Thus, a completely non-invasive intervention allows the
valve to be opened and possibly adjusted.
[0042] In a particular embodiment which is especially well suited
to the performance of a bone graft for the purpose of replacing an
injured vertebra, the shock-absorbing device comprises at least one
chamber formed of two semi-chambers joined by a bellows, each of
the semi-chambers being connected to one of the parts of the
implant, this chamber being filled with a hydraulic fluid, and at
least one calibrated opening being provided in a wall of this
chamber for connecting this chamber with another chamber.
[0043] This disposition has the advantage of being very compact and
preventing the relative slippage of the mechanical parts, with the
resulting risk of hydraulic fluid leakage. However, in certain
cases a traditional cylinder-and-piston shock-absorber may be
preferred.
[0044] More particularly, these semi-chambers can be in the form of
cupels whose openings face one another.
[0045] The above-mentioned locking means can in this case comprise
a removable elongated locking element, inserted into a fold of the
bellows so as to prevent it from collapsing.
[0046] The elongated locking element can be embodied in any
appropriate way, for example in the form of a metal beaded
chain.
[0047] The above-mentioned means for limiting the travel can
comprise a stop ring screwed onto one of the semi-chambers and
designed to cooperate with a shoulder of the other semi-chamber to
prevent the two semi-chambers from moving toward one another beyond
a certain limit.
[0048] The other chamber can be housed in a supporting skirt
mounted on one of the semi-chambers around the calibrated opening,
opposite the other semi chamber.
[0049] This other chamber can also be formed of two semi-chambers
joined by a bellows.
[0050] In a preferred embodiment, the implant according to the
invention also includes elastic means between these two parts.
[0051] In effect, it is often beneficial for the resistance to the
relative displacement of the two parts of the implant to be
proportional not only to the speed of this displacement, but also
to the value of this displacement itself relative to a nominal
position. Thus, the implant's assistance to the surrounding bone
structures is even more efficient when they are farther apart than
in their normal configuration.
[0052] Advantageously, the coefficient of elasticity is
adjustable.
[0053] Thus, it is possible to adjust the elasticity of the implant
and, for example, to render it increasingly flexible as the
surrounding structure re-establish themselves.
[0054] This type of elasticity can be obtained in an implant
comprising two chambers filled with hydraulic fluid and joined by a
calibrated opening, at least one of which chambers contains a
compression ampulla at ambient pressure with elastic walls.
[0055] When a movement between the two parts of the implant begins,
it produces a pressure variation in the chambers, and thus an
elastic reaction of the compressible ampulla.
[0056] The wall of this ampulla can have progressive elasticity,
one of the chambers being capable of being joined to a source of
fluid under pressure.
[0057] Thus, in this case, it is possible to regulate the
elasticity of the implant by adjusting the pressure in the
cambers.
[0058] Means can be provided for adjusting the cross section of the
calibrated opening.
[0059] In particular, these means for adjusting the cross section
of the calibrated opening can comprise a hydraulically controlled
needle valve.
[0060] Another subject of the present invention is an implant of
the type described above wherein the shock-absorbing device
comprises at least two chambers, specifically two low-pressure
chambers whose walls are made of elastic material, these chambers
being jointed by at least one calibrated conduit and filled with
hydraulic fluid, and designed to sustain a differential pressure
variation during a relative movement of the elements.
[0061] This type of design makes it possible to easily obtain
implants which, as above, not only have a viscous resistance which
is a function of the speed, but also an elastic resistance which is
a function of the displacement.
[0062] In this case, the cross-section of the conduit can
advantageously be determined by the prevailing pressure in a
high-pressure chamber which is capable of compressing this
conduit.
[0063] As a result of this design, the coefficient of resistance of
the implant can be regulated very easily by adjusting the pressure
in the high-pressure chamber.
[0064] In particular, one of the low-pressure chambers can have a
wall of relatively low rigidity relative to the rigidity of the
walls of the other chamber.
[0065] This design allows the implant to function even when the two
chambers are not stressed differently. During a movement which
creates excessive pressure, the pressure increases more in the
rigid-walled chamber, resulting in a flow of the hydraulic fluid
from this chamber to the chamber with the less rigid wall, and thus
a shock-absorbing effect.
[0066] In one particular embodiment, a high-pressure chamber and a
low-pressure chamber can be connected, in the low-pressure to
high-pressure direction, by a non-return valve.
[0067] As will be seen, this disposition makes it possible to
increase the pressure difference between the high-pressure and
low-pressure chambers. It also makes it possible to maintain this
difference despite possible leaks in the high-pressure to
low-pressure direction.
[0068] The anti-return valve can comprise a flexible tube connected
to the low-pressure chamber, one free end of which is inserted into
a free end of a tube connected to the high-pressure chamber.
[0069] This type of valve is very small and also has the advantage
of being even more tightly closed when the pressure difference is
greater.
[0070] Preferably, it is also arranged for these chambers to be
connected by a pressure regulation valve in parallel with the
anti-return valve.
[0071] It will be seen that the anti-return valve is preferably
disposed between the high-rigidity, low-pressure chamber and the
high-pressure chamber.
[0072] In one particular embodiment, the implant according to the
invention comprises a first annular low-pressure chamber, and a
second rotating chamber in the center of the first chamber, the
calibrated conduits being formed radially in the wall separating
the two chambers.
[0073] Advantageously, the outer wall of the first low-pressure
chamber is relatively thin, and the wall separating the two
low-pressure chambers if relatively thick.
[0074] This implant can comprise at least one annular high-pressure
chamber formed within the thickness of the wall separating the two
low-pressure chambers, and designed to compress the calibrated
conduits.
[0075] In another embodiment, this conduit is at least partially
embodied in the form of a tube of elastic material surrounded by a
tube that is substantially more rigid, these tubes being joined
into rings at their ends, the compressed volume between the two
tubes forming a high-pressure chamber.
[0076] In another particular embodiment, the implant is
substantially disk-shaped, comprising a plurality of low-pressure
chambers in sectors, joined by the calibrated conduits, which
alternate inside the thickness of the disk with the high-pressure
chambers.
[0077] Advantageously, the implant according to the invention
comprises means for adjusting the distance between the elements it
connects.
[0078] This type of design makes it possible, in particular, to
alleviate possible post-operative pain by adjusting this distance
appropriately. It is also particularly advantageous in the case of
prostheses intended for children who are still growing.
[0079] These adjusting means can comprise a bellows designed to
receive a hydraulic fluid, and means for connecting this bellows to
a source of fluid under pressure.
[0080] Another subject of the invention is a pair of implants as
described above, the low-pressure chamber of each of the implants
being connected by the anti-return valve to the high-pressure
chamber of the other implant.
[0081] A pair of implants of this type can particularly be
provided, in the case of a graft of the vertebral column, to assist
the graft in case of lateral flexion.
[0082] More generally, a pair of implants according to the
invention can include means for automatically adapting to the
movements of the wearer of the implants.
[0083] Up to this point, bone consolidation implants embodied
according to the invention have been described. It will now be
shown that the invention is also well suited to the embodiment of
articulated implants.
[0084] In this case, each part of an implant as described above is
articulated to the other.
[0085] More particularly, these parts can have complementary
surfaces which rest against one anther, forming a ball-and-socket
joint.
[0086] An articulated implant of this type can include, in
particular, a pivot integral with one of the parts and housed in a
space formed between a plurality of low-pressure chambers in the
form of sections, which are integral with the other part of the
implant and joined by the calibrated conduits, which themselves
alternate with high-pressure chambers.
[0087] These embodiments are suitable as intervertebral disks.
[0088] In a particular application to a coxofemoral joint, the
implant according to the invention comprises an articulating hollow
sphere whose wall is open so as to allow the insertion of the end
of a connecting pin, the shock-absorbing device being disposed
inside this sphere between the wall of the latter and the end of
the connecting pin.
[0089] More particularly, this shock-absorbing device can comprise
an end element of the connecting pin designed to slide through a
slot of a partition inside the sphere, which partition delimits two
chambers in the sphere, and at least one calibrated opening is
formed inside this end element between the two chambers.
[0090] In another embodiment, this shock-absorbing device can
include an end element of the connecting pin disposed between two
shock-absorbing elements, each of which includes at least two
low-pressure chambers whose walls are made of elastic material,
these chambers being connected by at least one calibrated conduit
and filled with hydraulic fluid, and designed to sustain a
differential pressure variation during a relative movement of the
sphere and the connecting pin.
[0091] Another subject of the invention is a pair of implants as
described above, used particularly within the scope of an
arthrodesis of the vertebral column, each of the implants being
mechanically connected in series to a connecting pin of a known
type.
[0092] More particularly, each of the implants can include means
for adjusting the distance between the two elements it
connects.
[0093] It is thus possible, using a pair of implants of this type,
not only to perform the arthrodesis, but also to adjust the angle
and the distance between the two parts of the vertebral column
connected by the prosthesis.
[0094] In one particular mode of embodiment, these adjusting means
include, for each implant, an expandable element such as a bellows,
designed to receive a hydraulic fluid, and means for connecting
this bellows to a source of fluid under pressure.
[0095] This source of fluid under pressure can comprise a
high-pressure fluid reservoir.
[0096] Advantageously, this high-pressure reservoir is common to
both implants, each expandable element is also connected to a
low-pressure reservoir, and an expandable refill cell is
mechanically connected in series to each pin, each refill cell
being connected to the high-pressure and low-pressure reservoirs by
two anti-return valves, one of which allows a flow of fluid from
the low-pressure reservoir to the refill cell, the other allowing a
flow of fluid from the refill cell to the high-pressure
reservoir.
[0097] It will be seen that this type of design makes it possible
to produce a pump activated by the movements of the wearer of the
implants.
[0098] In another particular embodiment, the above-mentioned pair
of implants if formed of implants in which the shock-absorbing
device comprises at least two chambers, these chambers being
connected by at least one calibrated conduit and filled with
hydraulic fluid, and designed to sustain a differential pressure
variation during a relative movement of these elements, the
cross-section of this calibrated conduit being determined by the
prevailing pressure in a high-pressure chamber, and the
high-pressure chambers of the implants are connected to the
high-pressure reservoir by a controllable valve.
[0099] Another subject of the invention is a skeletal implant as
described above, specifically belonging to a pair of implants,
which includes sensors of physical quantities, including pressure,
supplied with electric power and controlled from outside the body
in a non-invasive way, and designed to transmit their information
to display means.
[0100] More particularly, this implant can also include adjusting
actuators which are also supplied with electric power and
controlled from outside the body in a non-invasive way.
[0101] In facts the implants which were described have a variable
length or dimension, the two parts or ends of the implant being
able to move apart from one another or approach one another
actively and/or passively, for example along the longitudinal axis
of the implant, by virtue of the interposition of a deformable
element, for example a hydraulic element, control means and/or
regulating means being provided so as to make it possible to obtain
a change in dimension of the implant in order to modify the
distance between the two bone elements and/or to ensure an
adjustable viscous or viscoelastic damping permitting a slow
movement between the two bone elements and also counteracting a
more abrupt displacement.
[0102] If necessary, a sufficiently high hydraulic pressure can be
maintained by using the effect of a mechanical pump, actuated by
the movements of the body, with a pressure-limiting valve flap,
cooperating with a low-pressure reservoir.
[0103] For example, double implants consisting of two individual
implants can be disposed respectively on either side of the spine
in order to connect two vertebrae, each of the two elements thus
being fixed to a lower vertebra via an anchoring means, such as a
pedicle screw, and to an upper vertebra, either adjacent or more
distant, likewise each time by an anchoring means, such as a
pedicle screw.
[0104] In the case of a double implant consisting of two individual
implants acting on the same skeletal structures, the two individual
implants hydraulically can be interconnected in such a way as to
permit pivoting movements of the bone elements relative to one
another, namely a lateral pivoting in the frontal plane of the
spine, by increasing the length of one of the individual implants
and concomitantly reducing the length of the other implant, for a
correction of deformation and/or a damping of lateral flexion.
[0105] By virtue of control means, for example noninvasive means of
the magnetic type, it is possible to effect the desired
modifications to the dimension of the individual implants and/or
the modifications to the damping coefficient of the element acting
as a damper. Moreover, means can be provided for automatically
modifying the damping coefficient or the viscosity as a function of
the movements of the body.
[0106] In brief, the present invention proposes realizing and
perfecting an implantable device comprising at least one implant
equipped with two end parts which can be fixed, by anchoring means,
on at least two elements or parts of the skeleton, and comprising
means of displacement, preferably at least partially reversible,
between the said two ends, these means being arranged to provoke
and/or maintain a displacement between the said elements of the
skeleton.
[0107] This displacement can be a rectilinear and/or curved
displacement, for example it can be a displacement of elongation,
also called distraction, or a displacement of shortening, called
compression, or a displacement in rotation, it being possible for
this rotation to be isolated or, on the contrary, to be combined
with a distraction or a compression.
[0108] In the simplest embodiment, in which the said displacement
means are capable of maintaining but not provoking the
displacement, these displacement means are controlled by control
means, preferably noninvasive ones, which make it possible to
release them so as to allow the patient, or another party, to
modify the relative position of the two portions or elements of the
skeleton, after which the said control means are actuated in order
to block the implant in this new position, an inverse or reversible
displacement still remaining possible if one acts once more on the
control means, for example in the case where the displacements
would have been too great.
[0109] In another preferred embodiment of the invention, the said
displacement means include a motor means with which it is possible
to impose a displacement between the said ends by exerting a force
between them.
[0110] In a particular embodiment, this force can be exerted
temporarily, that is to say for quite a brief instant, far the
purpose of provoking a therapeutically desirable displacement
between the two portions or elements of the skeleton, such a
displacement often being intended for a small amplitude, since it
is rapidly impeded by the anatomical structures which must not be
traumatized. At the end of this instant, the control means make it
possible to block the two ends relative to one another and to
maintain the implant in its new position.
[0111] In another embodiment, by contrast, the said displacement
means are capable of exerting an anatomically active permanent
force between the said two ends, it being possible for this force
to be constant or variable in such a way as to exert on the
anatomical environment a stress which will gradually permit an
anatomically desired displacement between the said two portions or
elements of the skeleton, these motor means being controllable by
control means with which it is possible to permit or interrupt
their functioning and/or to adjust the intensity of the force.
[0112] If appropriate, the implant can also include viscous or
viscoelastic damping means which can be used when the implant is
blocked in its dimension or when the implant is freed or when it
exerts its permanent active force. Such means have been described
in the abovementioned European and American applications.
[0113] The said means of displacement and, if necessary, the said
motor means can be of the hydraulic and/or mechanical and/or
electrical type, a hydraulic type being preferred.
[0114] In one embodiment using hydraulic means, the implant
preferably includes: two parts or end elements, for example rods,
each receiving at least one means for anchoring in a skeletal part;
at least one deformable element, preferably hydraulic, interposed
between the said two elements, and permitting a variation in
dimension and/or the creation of an active force between them;
preferably at least one high-pressure reservoir, called a reserve,
with which it is possible to address the high pressure, on demand,
to a functional user circuit; preferably at least one low-pressure
collection reservoir connected to the high-pressure reservoir via a
pressure control valve; preferably at least one circuit for
recharging the high-pressure reservoir, comprising at least one
deformable element, preferably sensitive to physical positions or
movements of the body receiving the implant; to generate a high
pressure which, if so required, feeds the high-pressure reservoir;
at least one functional circuit, namely: a circuit for modifying
the dimension, for example the length, of the implant, comprising
the said deformable element with which it is possible to modify a
dimension between the two end elements and/or to establish, between
the two end elements, an active force capable of provoking a
progressive modification of the dimension between the said end
elements, the said deformable element being connected on the one
hand to the high-pressure reserve reservoir by way of a first valve
and, on the other hand, to the low-pressure collection reservoir by
way of a second valve in order to make it possible, as a function
of the control of the said valves, to increase and/or reduce the
dimension of the said deformable element in order to permit or
provoke a lasting modification to the said dimension of the said
individual implant, and/or a viscous or viscoelastic damping
circuit comprising: if appropriate, an elastic element surgically
interposed between the said two end elements of the implant, and a
hydraulic damping element comprising at least one deformable
element sensitive to the speed of a dimensional variation of the
implant and communicating with a discharge reservoir by way of a
throttle means, and control means which can preferably be actuated
from outside the body of the patient, in order to modify the
dimension of the implant and/or the force exerted by the implant
and/or the damping properties.
[0115] Of course, one and the same piece, for example a deformable
element, can form a constituent part of several of the constituents
defined hereinabove.
[0116] The circuit for recharging the high-pressure reservoir is in
fact intended to act as a very high-pressure pump, making it
possible to establish and to maintain a high pressure in a
high-pressure reservoir
[0117] Preferably, especially in the preferred case where the
deformable element of the high-pressure recharging circuit is
sensitive to physical positions or movements of the patient
receiving the implant, this deformable element has a small surface
compared with the active surface of the element which transmits to
it the force originating from the body, in such a way as to ensure
a pressure-multiplying differential effect, it being understood
that upon each stress only a small quantity of very high-pressure
fluid is sent towards the high-pressure chamber.
[0118] The deformable element of the circuit for recharging the
high-pressure reservoir can also be actuated by external means
while remaining implanted. Thus, for example, this deformable
element can be in the form of a pump, preferably formed by a metal
bellows, implanted on a part of the body at a point where an
external pressure can be applied to it, for example implanted on
the posterior face of the sacrum, allowing this pump or bellows to
be actuated by hand via the external anatomical planes.
[0119] Alternatively, this pump could be of the magnetic or
electromagnetic type, having, for example, a movable core actuating
a small piston or bellows under the influence of an electromagnetic
force of external origin.
[0120] It will also be appreciated that the present application
incorporates the alternatives and equivalents using non-hydraulic
motor and/or damping means, ensuring the same functions of lasting
and adjustable modification of dimension and/or force and/or
adjustable modification or variation of the damping
coefficient.
[0121] Solely by way of example, an implant of the uniquely
mechanical type can comprise a first end, movable in translation
relative to the second end, and secured to a rod which is
immobilized by a catch which is sensitive to an external magnetic
control means for blocking or releasing the said rod, a motor means
being interposed between the said rod and the said second end, it
being possible for this motor means to be in the form of a spring
or another precharged elastic element tending to displace one of
the ends relative to the other when the catch is released, it being
possible for the movement to be reversible, at least once, for
example by inserting, between the spring and the said second end, a
spring support piece which can be displaced, by virtue of other
magnetic control means, in such away as to at least partially relax
the spring. Alternatively, the implant can include several springs
arranged in parallel and capable of being used separately by
release means which are sensitive to control means.
[0122] In another embodiment, an implant can include displacement
means of the electromagnetic type, for example a solenoid with a
plunger core, the solenoid being secured to one of the ends of an
implant and the plunger core being secured to the other end,
blocking means preferably being provided for immobilizing the core
relative to the solenoid in at least two different positions, the
solenoid being capable of being powered, via a control means, from
an electrical energy source, for example an implanted battery
and/or an accumulator which can be recharged by antenna
transmission with transcutaneous coupling.
[0123] Such embodiments are reversible within the meaning of the
invention because, if so desired, they permit a modification in the
opposite direction, at least partially, of the dimensional
modification which has been established.
[0124] The present invention also makes it possible to perfect the
movements or forces of rotation permitted or imposed by an implant
or a set of at least two individual implants in the frontal and/or
sagittal and/or horizontal plane.
[0125] For example, the invention can provide implants of this type
with which it is possible to impose symmetrical movements of
rotation, that is to say in the same direction and of the same
value of rotation, of the pedicle screws or similar anchoring means
of the two individual implant parts, or, by contrast,
antisymmetrical movements, that is to say in opposite directions,
or else independent of one another.
[0126] Generally speaking, the movement or force of rotation
controlled between the two anchoring means of an implant according
to the invention and, where appropriate, the coordination of the
movements or forces of rotation of the anchoring means of several
implants, for example the individual implants of a double implant,
will make it possible, depending on requirements, to approximate
much more closely the theoretically possible or desirable natural
movement between the two bone parts to which the anchoring means
are fixed, so as to impose progressive displacements, for example
for corrections, and/or progressively modifiable damping, ranging,
for example, from rigidity during a phase of bone consolidation or
healing to progressive mobility, making it possible, for example,
to safeguard a joint.
[0127] The skeletal implant has a first and a second part or end
element, means for anchoring in bone parts, which means are
connected respectively to the said first and second end elements,
at least one deformable element connected respectively to the said
first and second anchoring means, and means permitting a
nonrectilinear movement, particularly a rotation, between the said
anchoring means.
[0128] The implant can include means permitting a rotation between
the said end elements.
[0129] The said deformable element can be deformable in
rotation.
[0130] The implant can include means permitting a rotation of at
least one of the said anchoring means relative to the end piece to
which it is connected.
[0131] The abovementioned movement of rotation can also be combined
with movements of translation, in such a way that the resulting
movement can be a complex nonrectilinear displacement.
[0132] According to one refinement, the skeletal implant, having a
first and a second end element, means for anchoring in bone parts,
for example by way of screws, such as, for example, pedicle screws
situated at the said ends, at least one deformable element, for
example a hydraulic element, containing an incompressible hydraulic
fluid and interposed between the two end elements, and means for
actuating the deformable element, for example, if necessary,
hydraulic circuit means connected to the said at least one
deformable element interposed between the said ends, and capable of
permitting a lasting modification, preferably obtained
progressively, of the distance or the force between the said two
ends and/or a viscoelastic damping of the movements between the
said two ends, the said actuating means, for example the said
hydraulic circuit means, being sensitive to control means which can
preferably be actuated from outside the body of the patient, is
characterized in that the said fixing or anchoring means are fixed
to the said two ends by articulated attachment means, and in that
the said fixing or anchoring means are additionally connected to
one another via a rigid joining element which is relatively
parallel to the geometric axis connecting the said two ends of the
implant and is situated at a certain distance from the said axis,
by attachment means which are likewise articulated, for example in
such a way as to form between the said four attachment points a
deformable quadrilateral, permitting an angular movement of
rotation of the said fixing or anchoring means relative to one
another.
[0133] These articulated attachment means can consist of actual
mechanical articulations or of suitably deformable joining
means.
[0134] For example, the articulations can be articulations using a
ball which is received rotatably in a seat of the end piece, this
ball having a passage through which it can receive and hold a part
of an anchoring means, such as a pedicle screw. Of course, all
other articulation principles such as a pivot articulation can be
used.
[0135] In one embodiment, the said joining element is situated
between the axis of the implant and the bone elements to which the
implant is fixed, but in another embodiment the said joining
element is arranged on the other side of the axis of the implant in
relation to the bone elements which are joined by the implant.
[0136] The said joining elements can be simple rigid links such as
rods or bars of invariable length.
[0137] However, in another embodiment, these joining elements
themselves can include, between their ends, at least one deformable
zone, which then makes it possible to effect displacements, such
as, for example, an elongation of the implant without relative
rotation of the fixing means, by simultaneous modification of the
length of the actual element and of the joining element, and/or to
effect a viscoelastic damping between the bone elements without any
movement of rotation of the said fixing means.
[0138] A complex implant in accordance with the invention can be
formed by using two individual implants arranged, for example, side
by side, for example on either side of the spinous processes of the
vertebral column, with a hydraulic interconnection making it
possible to effect at least one of the following functions:
antisymmetrical rotation movement of the means of one individual
implant relative to the movement of the anchoring means of the
other implant, symmetrical movements of the said anchoring means,
independent movements.
[0139] Of course, for the sake of simplicity, the two individual
elements of a complex implant can use common hydraulic elements,
such as, for example, high-pressure reservoir, low-pressure
collector, means for creating the high pressure, and means for
controlling the hydraulic circuit.
[0140] In another embodiment, intended to permit a rotation in a
transverse plane, or, if appropriate, an oblique plane, relative to
the general direction of the implant, that is to say the direction
connecting the two anchoring means or screws, the skeletal implant,
having a first and a second end element, means for fixing or
anchoring in bone parts, for example by way of screws, for example
pedicle screws situated at the ends, at least one deformable
element interposed between the two end elements, and its actuating
means, to permit a lasting modification, preferably obtained
progressively, of the distance between one end and an element
movable relative to the said one end, and control means, which can
preferably be actuated from outside the body of the patient, is
characterized in that the said movable element is arranged to
provoke or permit a rotation of the other of the two ends about an
axis substantially parallel to the said implant.
[0141] The means by which the displacement of the said movable
element by the movement of the deformable element transforms this
movement into a movement of rotation of the said other end, and of
the fixing or anchoring means which it supports, can be a means
combining a screw and a nut in such a way that the movement of
translation of the one provokes a movement of rotation of the
other.
[0142] In a particular embodiment, the deformable element is
interposed between the two end pieces, one of which is capable of
turning, in such a way that the deformation of the deformable
element entrains at one and the same time a rotation and a
translation of one of the end elements, and thus of the anchoring
means which it bears, relative to the other end piece, translating
into a helical movement of one of the end pieces relative to the
other.
[0143] In another embodiment, the two end pieces can be secured to
one another in such a way as to remain spaced apart by an
invariable distance, the movable element then being interposed
between this assembly of end elements and the means for
transforming the deformation of the movable element into a rotation
of one of the end elements relative to the other.
[0144] In another embodiment, it is the deformable element itself
which is constructed to deform in rotation, for example by using a
deformable chamber with rotary piston, according to the well-known
principles of hydraulic rotation.
[0145] Devices capable of rotation, such as have just been
described, can be particularly useful in cases of severe scoliosis
or serious degenerative destabilization of the spine. In these
cases, it will for example be possible to fix two devices according
to the invention on either side of the posterior process of the
vertebra, between two vertebral levels, and to provoke rotation
between the two anchoring points of one of the two devices, or a
rotation combined with a longitudinal displacement, the other
device then being capable of a complementary movement of geometric
adaptation of the displacements imposed by the first one.
[0146] All kinds of complex nonrectilinear displacements can be
obtained by means of the intervention, for example by subjecting
the displacement of an anchoring means, or of an end piece, to a
cam or slide or other curved guide.
[0147] The implant consisting of a device according to the
invention will preferably have an external shape suitably adapted
to the physical environment in which it is located. For example, in
particular for vertebral implants, it will be advantageous to give
each of the two ends a streamlined shape so as not to disturb the
adjacent tissues, especially since, by virtue of the implants
according to the invention, it is possible to achieve a functional
improvement which should involve the muscles and ligaments, in
contrast to arthrodeses which cause their atrophy.
[0148] This streamlined shape can comprise an envelope, which is
preferably deformable and is applied around the implant, and of
which the two ends which having the fixing means for the anchoring
means emerge from the envelope, the latter containing the various
other components of the implant. The free internal volume in this
envelope can preferably serve as a low-pressure liquid reservoir.
The implant preferably includes, inside this envelope, the movable
element which can be a mechanical motor or preferably a hydraulic
motor, for example a hydraulic bellows, the interior of which is
connected via a low-pressure valve to the low-pressure volume
formed in the envelope.
[0149] Preferably, the interior of the envelope also includes a
high-pressure reservoir, preferably a bellows, and, again
preferably, a differential deformable element for sending liquid at
very high pressure into the high-pressure reservoir, the
high-pressure reservoir being connected to the moveable element
likewise via a high-pressure valve, the high-pressure valve and the
low-pressure valve preferably being relatively spaced apart from
one another in order to easily permit a selective control by
external control means, such as, for example, magnets.
[0150] However, in another embodiment, particularly when a
succession of individual implants is provided at various levels of
the spine, it is also possible to provide a single high-pressure
reservoir and/or a single recharging means for recharging the
high-pressure reservoirs, which is situated away from the various
individual implants and is connected to these by inextensible
conduits.
[0151] The high-pressure reservoir can advantageously be designed
to maintain the liquid which it contains at high pressure, even
when significant quantities of this liquid are sent to the motor
means of the implant, provoking a substantial reduction in the
volume of liquid. This can be effected, for example, by designing
the high-pressure reservoir in the form of an elastically
deformable reservoir of great stiffness, for example a metal
bellows of great stiffness, which is expanded when it contains the
liquid at high pressure, this bellows tending to retract in order
to maintain the high pressure during a substantial part of its
retraction travel. Alternatively, or in combination with such a
bellows, it is also possible, in order to maintain the high value
of pressure in the reservoir, to provide an energy accumulator in
the form of a cell with an elastically deformable wall which is
compressed, thus reduced in volume, when the high-pressure liquid
is introduced into the high-pressure reservoir, and which relaxes
elastically while at the same time maintaining a high pressure when
liquid is withdrawn from the high-pressure reservoir. This energy
accumulator is preferably in the form of a deformable capsule which
can, for example, comprise in its interior an easily deformable
substance or a gas, but which particularly preferably has a
substantial vacuum so as to eliminate any risk of escape of
gas.
[0152] The invention also provides for a skeletal implant of the
type to be used to connect at least two elements of a skeleton,
wherein the skeletal implant comprises a first part adapted to be
connected to at least one of the at least two elements of the
skeleton, a second part adapted to be connected to another of the
at least two elements of the skeleton, a variable volume element
adapted to move the first and second parts with respect to each
other, a high-pressure chamber supplying fluid to the variable
volume element a low-pressure chamber receiving fluid from the
variable volume element and a recharging variable volume element is
adapted to communicate with the high-pressure chamber and the
low-pressure chamber.
[0153] The implant may further comprise another variable volume
element disposed in the high-pressure chamber.
[0154] The implant may further comprise a high-pressure valve
allowing fluid to enter the variable volume element from the
high-pressure chamber.
[0155] The low-pressure chamber may comprise a deformable
impermeable sleeve.
[0156] The implant may further comprise a low-pressure valve
allowing fluid to exit the variable volume element and enter the
low-pressure chamber.
[0157] The implant may further comprise a third part having one end
coupled to the first part and another end disposed between the
variable volume element and the second part.
[0158] The variable volume element may comprise one end coupled to
the first part and another end coupled to a third part.
[0159] The implant may further comprise a third part having a
threaded opening which engages a threaded portion of the second
part.
[0160] The recharging variable volume element may comprise one end
that is coupled to a third part and another end that is coupled to
the first part. The second part may be rotatably coupled to at
least one of the variable volume element and the third part.
[0161] The implant may further comprise a sealed bellows disposed
in the high-pressure chamber.
[0162] The recharging variable volume element may be a metal
bellows having one end coupled to the first part and another end
coupled to a third part.
[0163] The implant may further comprise a sleeve defining a
variable volume of the low-pressure chamber.
[0164] The implant may further comprise a high-pressure conduit
connecting the variable volume element to the high-pressure
chamber.
[0165] The variable volume element may comprise a metal bellows. At
least one of the first part and the second part may comprise an
opening which is adapted to receive a connecting member, whereby
the connecting member connects the first or second part to one of
the at least two elements of the skeleton.
[0166] The invention also provides for a skeletal implant of the
type to be used to connect at least two elements of a skeleton,
wherein the skeletal implant comprises a first part adapted to be
connected to at least one of the at least two elements of the
skeleton, a second part adapted to be connected to another of the
at least two elements of the skeleton, a variable volume element
having a first end coupled to the first part and a second end, the
variable volume element being adapted to move the first and second
parts away from each other, a third part having a first end coupled
to the first part and a second end coupled to the second end of the
variable volume element, a high-pressure chamber supplying fluid to
the variable volume element, and a low-pressure chamber receiving
fluid from the variable volume element.
[0167] The implant may further comprise a recharging variable
volume element which includes a first end coupled to the first end
of the third part and a second end coupled to the first part.
[0168] The recharging variable volume element may be adapted to
communicate with at least one of the high-pressure chamber and the
low-pressure chamber. The second part may be rotatably coupled to
at least one of the variable volume element and the third part.
[0169] The implant may further comprise a high-pressure valve
allowing fluid to enter the variable volume element from the
high-pressure chamber.
[0170] The implant may further comprise a low-pressure valve
allowing fluid to exit the variable volume element and enter the
low-pressure chamber. At least one of the first part and the second
part may comprise an opening which is adapted to receive a
connecting member, whereby the connecting member connects the first
or second part to one of the at least two elements of the
skeleton.
[0171] The invention also provides for a skeletal implant of the
type to be used to connect at least two elements of a skeleton,
said implant comprising at least two parts, each of which is
capable of being connected to one of said at least two elements,
said at least two parts being movable with respect to each other,
wherein there is provided, between said at least two parts at least
one of a means authorizing a displacement between said at least to
parts, from a starting position to a displaced position and a means
exerting a force between said at least two elements of the
skeleton. Said means is responsive to control means and comprises
at least one variable volume element containing a fluid. Said
control means comprises a high-pressure reservoir and a very
high-pressure differential variable volume recharging element for
sending fluid at high-pressure into said high-pressure reservoir.
Said high-pressure reservoir is connected to said at least one
variable volume element via a high-pressure valve. Said at least
one variable volume element is connected to a low-pressure
reservoir via a low-pressure valve. Said very high-pressure
differential variable volume recharging element is connected to
said low-pressure reservoir via another low-pressure valve. Said
very high-pressure differential variable volume recharging element
is responsive to displacements of corporal parts for recharging of
said high-pressure reservoir with said fluid.
[0172] Said high-pressure reservoir may be designed to maintain
said fluid contained therein at high pressure, even when
significant quantities of said fluid are sent to said variable
volume element, provoking a substantial reduction in a volume of
said fluid, in order to maintain a high value of pressure in said
high-pressure reservoir, and wherein said high-pressure reservoir
contains an energy accumulator in the form of a cell having an
elastically deformable wall, said energy accumulator being
configured to assume a compressed and reduced volume state when
fluid is introduced into said high-pressure reservoir, and being
configured to assume an expanded state to maintain a high pressure
when fluid is withdrawn from said high-pressure reservoir.
[0173] The invention also provides for a skeletal implant of the
type to be used to connect at least two elements of a skeleton,
said implant comprising at least two parts, each of which is
capable of being connected to one of said at least two elements,
said at least two parts being movable with respect to each other,
wherein there is provided, between said at least two parts at least
one of a means authorizing a displacement between said at least to
parts from a starting position to a displaced position wherein the
means comprises at least one variable volume element containing a
fluid and a means exerting a force between said at least two
elements of the skeleton. Said means is responsive to control
means. Said control means comprises a high-pressure reservoir and a
very high-pressure differential variable volume recharging element
for sending fluid into said high-pressure reservoir. Said
high-pressure reservoir is connected to said variable volume
element via a high-pressure valve. Said variable volume element is
connected to a low-pressure reservoir via a low-pressure valve.
Said high-pressure valve and said low-pressure valve are relatively
spaced apart from one another.
[0174] The invention also provides for a skeletal implant of the
type to be used to connect at least two elements of a skeleton
wherein the skeletal implant comprises a first part adapted to be
connected to at least one of the at least two elements of the
skeleton. A second part is adapted to be connected to another of
the at least two elements of the skeleton. A variable volume
element is adapted to move the first and second parts with respect
to each other. A high-pressure chamber supplies fluid to the
variable volume element. A low-pressure chamber receives fluid from
the variable volume element. A recharging variable volume element
is adapted to communicate with the high-pressure chamber and the
low-pressure chamber. The recharging variable volume element is
responsive to displacements of corporal parts of a user and
recharges the high-pressure chamber with fluid.
[0175] The implant may further comprise another variable volume
element disposed in the high-pressure chamber. The implant may
further comprise a high-pressure valve allowing fluid to enter the
variable volume element from the high-pressure chamber. The
low-pressure chamber may comprise a deformable impermeable sleeve.
The implant may further comprise a low-pressure valve allowing
fluid to exit the variable volume element and enter the
low-pressure chamber. The implant may further comprise a third part
having one end coupled to the first part and another end disposed
between the variable volume element and the second part. The
variable volume element may comprise one end coupled to the first
part and another end coupled to a third part. The implant may
further comprise a third part having a threaded opening which
engages a threaded portion of the second part. The recharging
variable volume element may comprise one end that is coupled to a
third part and another end that is coupled to the first part. The
second part may be rotatably coupled to at least one of the
variable volume element and the third part.
[0176] The implant may further comprise a sealed bellows disposed
in the high-pressure chamber. The recharging variable volume
element may comprise a metal bellows having one end coupled to the
first part and another end coupled to a third part. The implant may
further comprise a sleeve defining a variable volume of the
low-pressure chamber. The implant may further comprise a
high-pressure conduit connecting the variable volume element to the
high-pressure chamber. The variable volume element may comprise a
metal bellows. At least one of the first part and the second part
may comprise an opening which is adapted to receive a connecting
member, whereby the connecting member connects the first or second
part to one of the at least two elements of the skeleton.
[0177] The invention also provides for a skeletal implant of the
type to be used to connect at least two elements of a skeleton,
wherein the skeletal implant comprises a first part adapted to be
connected to at least one of the at least two elements of the
skeleton. A second part is adapted to be connected to another of
the at least two elements of the skeleton. A variable volume
element is adapted to move the first and second parts with respect
to each other. A high-pressure chamber supplies fluid to the
variable volume element. A low-pressure chamber receives fluid from
the variable volume element. A recharging variable volume element
is adapted to communicate with the high-pressure chamber and the
low-pressure chamber. The implant is adapted to provide a damping
effect with an adjustable coefficient of resistance.
[0178] The invention also provides for a skeletal implant of the
type to be used to connect at least two elements of a skeleton,
wherein the skeletal implant comprises a first part adapted to be
connected to at least one of the at least two elements of the
skeleton. A second part is adapted to be connected to another of
the at least two elements of the skeleton. A variable volume
element has a first end coupled to the first part and a second end,
the variable volume element being adapted to move the first and
second parts away from each other. A third part has a first end
coupled to the first part and a second end coupled to the second
end of the variable volume element. A high-pressure chamber
supplies fluid to the variable volume element. A low-pressure
chamber receives fluid from the variable volume element. A
recharging variable volume element is responsive to displacements
of corporal parts of a user and recharging the high-pressure
chamber with fluid.
[0179] The recharging variable volume element may include a first
end coupled to the first end of the third part and a second end
coupled to the first part. The recharging variable volume element
may be adapted to communicate with at least one of the
high-pressure chamber and the low-pressure chamber. The second part
may be rotatably coupled to at least one of the variable volume
element and the third part. The implant may further comprise a
high-pressure valve allowing fluid to enter the variable volume
element from the high-pressure chamber. The implant may further
comprise a low-pressure valve allowing fluid to exit the variable
volume element and enter the low-pressure chamber. At least one of
the first part and the second part may comprise an opening which is
adapted to receive a connecting member, whereby the connecting
member connects the first or second part to one of the at least two
elements of the skeleton.
[0180] The invention also provides for a skeletal implant of the
type to be used to connect at least two elements of a skeleton,
wherein the skeletal implant comprises a first part adapted to be
connected to at least one of the at least two elements of the
skeleton. A second part is adapted to be connected to another of
the at least two elements of the skeleton. A variable volume
element has a first end coupled to the first part and a second end,
the variable volume element being adapted to move the first and
second parts away from each other. A third part has a first end
coupled to the first part and a second end coupled to the second
end of the variable volume element. A high-pressure chamber
supplies fluid to the variable volume element. A low-pressure
chamber receives fluid from the variable volume element. A
recharging variable volume element is responsive to displacements
of corporal parts of a user and recharging the high-pressure
chamber with fluid. The implant is adapted to provide a damping
effect with an adjustable coefficient of resistance.
BRIEF DESCRIPTION OF DRAWINGS
[0181] Particular embodiments of the invention will now be
described, by way of a non-limiting example, in reference to the
appended schematic drawings, in which:
[0182] FIGS. 1a and 1b schematically illustrate the principal of
the invention applied to the formation of a callus after the
fracture of a long bone;
[0183] FIG. 2 schematically illustrates a femoral reconstruction
process after a fracture of the neck;
[0184] FIG. 3 shows a screw according to the invention which can be
used to implement the process of FIG. 2;
[0185] FIG. 4 is a larger-scale view of the detail IV of FIG.
3;
[0186] FIG. 5 is an even larger-scale axial section of the detail
IV;
[0187] FIG. 6 is a schematic axial section illustrating the
functioning of this screw;
[0188] FIG. 7 is a schematic axial section of a shock-absorbing
device which can be used in an implant according to the
invention;
[0189] FIG. 8 is a partial view of the device of FIG. 7 showing a
certain number of improvements;
[0190] FIG. 9 is a partial section along the line IX-IX of FIG.
8;
[0191] FIG. 10 is a view in perspective of elements of FIGS. 8 and
9;
[0192] FIGS. 11a and 11b are also partial views of the device of
FIG. 7 showing other improvements, in two successive phases of the
utilization of the device;
[0193] FIG. 12 is a front view in partial section of a rachidian
implant embodied according to the invention;
[0194] FIG. 13 shows the utilization of two implants according to
the invention within the scope of a rachidian arthrodesis;
[0195] FIG. 14 shows in detail, in axial section, the implants of
FIG. 13, in section along the line XIV-XIV of FIG. 15, and their
interconnections;
[0196] FIG. 15 is a cross-sectional view along the line XV-XV of
FIG. 14;
[0197] FIG. 16 is a diagram of the device of FIGS. 13 through
15;
[0198] FIGS. 17a through 17d illustrate the functioning of the
devices of FIGS. 13 through 16;
[0199] FIG. 18 shows a top view, in partial cross-section, of
another embodiment of a rachidian prosthesis according to the
invention;
[0200] FIG. 19 is a sectional view along the line XIX-XIX of FIG.
18;
[0201] FIG. 20 is a sectional view along the line XX-XX of FIG.
18;
[0202] FIG. 21 is a sectional view along the line XXI-XXI of FIG.
18;
[0203] FIG. 22 illustrates the interconnection of the chambers of
the prosthesis of FIG. 18;
[0204] FIG. 23 shows another possible assembly of two implants like
those shown in FIG. 14;
[0205] FIG. 24 illustrates a variant of FIG. 23;
[0206] FIG. 25 is a schematic axial section of an application of
the invention to an intervertebral prosthesis;
[0207] FIG. 26 shows the implantation of the prosthesis of FIG.
25;
[0208] FIG. 27 is an axial sectional view of a "ligament" of FIG.
26;
[0209] FIG. 28 shows a schematic top view of an embodiment of an
intervertebral prosthesis according to the invention;
[0210] FIG. 29 is a sectional view along the line XXIX-XXIX of FIG.
28;
[0211] FIG. 30 is a sectional view along the line XXX-XXX of FIG.
28;
[0212] FIG. 31 is a sectional view along the line XXXI-XXXI of FIG.
28;
[0213] FIG. 32 is a view in perspective showing in greater detail
the implantation of the intervertebral prosthesis of FIGS. 28
through 31;
[0214] FIG. 33 is a view in perspective of an anti-return valve
which can be used in an implant according to the invention;
[0215] FIG. 34 is an axial sectional view;
[0216] FIGS. 35 and 36 are views in perspective of a coxofemoral
prosthesis embodied according to the invention;
[0217] FIG. 37 is a schematic cross-sectional view;
[0218] FIG. 38 is a sectional view of the head of the prosthesis of
FIGS. 35 through 37;
[0219] FIG. 39 is a partially exploded view of the prosthesis of
FIGS. 35 through 38;
[0220] FIG. 40 shows another implant which can be used in place of
those in FIG. 13;
[0221] FIG. 41 is a view in perspective of an element of the
implant of FIG. 40;
[0222] FIG. 42 is an axial sectional view;
[0223] FIG. 43 is a view similar to FIG. 41 of another
embodiment;
[0224] FIG. 44 is an axial sectional view of this embodiment;
[0225] FIG. 45 illustrates the functioning of the elements of FIGS.
41 through 44;
[0226] FIG. 46 illustrates another mode of functioning of this
embodiment;
[0227] FIG. 47 is a schematic view of the entire hydraulic circuit
of an arthrodesis of the vertebral column using implants of the
same type as the one in FIG. 40;
[0228] FIG. 48 shows a possible implantation of the invention on a
spine;
[0229] FIG. 49 shows an electrical wiring diagram of the control of
an implant according to the invention;
[0230] FIG. 50 shows a diagrammatic view of a pair of implants for
antisymmetrical rotations according to a first embodiment of the
invention;
[0231] FIG. 51 shows another embodiment of such a pair of
implants;
[0232] FIG. 52 shows another embodiment of such a pair of
implants;
[0233] FIG. 53 shows one particular embodiment of an implant from
FIG. 52;
[0234] FIG. 54 shows a view of a pair of implants according to the
invention for symmetrical rotation movements according to a first
embodiment;
[0235] FIG. 55 shows a second embodiment of such a pair of
implants;
[0236] FIG. 56 shows a third embodiment of a pair of implants for
symmetrical rotations;
[0237] FIG. 57 shows a view of an embodiment of an implant from
FIG. 56;
[0238] FIG. 58 shows a diagrammatic view of a pair of implants, one
of which permits a simultaneous axial and rotational movement in a
plane transverse to the general direction of the implant;
[0239] FIG. 59 shows a diagrammatic view of a pair of implants, one
of which permits a rotation without translation movement, in a
plane perpendicular to the general direction of the implant;
[0240] FIG. 60 shows a side view of an embodiment of an implant
according to FIG. 58:
[0241] FIG. 61 shows a front view with partial sectioning of this
implant;
[0242] FIG. 62 shows a front view, with partial sectioning, of an
implant according to an embodiment from FIG. 59; and
[0243] FIG. 63 shows a cross section of a detailed embodiment of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0244] FIGS. 1a and 1b represent a long bone 1 in whose middle part
2 a graft 3 has been formed, between two end elements 4 and 5.
[0245] An implant, generally designated by the reference number 6,
is provided in order to consolidate the graft 3. For this purpose,
the implant 6 comprises two parts 7 and 8, each of which is screwed
into one of the bone elements 4 and 5, respectively. According to
the invention, the opposite ends of the parts 7 and 8 are connected
by a shock-absorbing device.
[0246] The shock absorber 9 is composed in a known way of a
cylinder 10 which forms two closed chambers 11 and 12 respectively,
separated by a piston head 13, mounted such that it slides in the
cylinder. For this purpose, the cylinder 10 is filled with a
hydraulic fluid, which can be laminated at the level of a
calibrated opening (not represented) formed in the piston head
13.
[0247] Means of any known type, also not represented, are provided
for adjusting the coefficient of resistance, for example means for
adjusting the cross-section of the calibrated opening. Adjusting
means of this type are present in all the embodiments described
below, even in the cases where they are not mentioned.
[0248] The end of the part 7 of the implant is connected to a
piston rod 14 attached to the head 13 and passing through one of
the end plates of the cylinder. The end of the part 8 of the
implant is connected to the cylinder 10.
[0249] Moreover, a removable rigid connecting piece 15 initially
connects the end parts 7 and 8 of the implant, thus making the
shock absorber 9 inactive.
[0250] The implant 6 is put in place with its connecting piece 15
(FIG. 1a), which is retained as long as no callus has formed at the
level of the graft. Due to this connecting piece, the implant
behaves like a standard implant, sustaining both the static and
dynamic stresses. When the callus has formed (FIG. 1b), the
connecting piece 15 is removed or inhibited.
[0251] Since the shock absorber exerts between the parts 7 and 8 of
the implant 9 a force proportional to the relative speed of these
two parts, the partially reconstituted bone will sustain all of the
static stresses. On the other hand, it will be increasingly
assisted by the shock absorber as the dynamic stresses it sustains
become more substantial, thus causing high rates of strain, in this
case tensile strain or compressive strain.
[0252] FIGS. 2 through 6 show an application of the principle
explained in reference to FIGS. 1a and 1b.
[0253] These figures show the top part of a femur 100 which has
sustained a fracture at the level of the neck 101. In a known way,
a screw 103 is inserted into the body of the femur and into its
head 104, in order to hold the latter in place until the formation
of a callus and the suture of the two parts separated by the
fracture.
[0254] The screw 103 is embodied in two rigid substantially
cylindrical parts, namely a body 105, the part of the screw nearest
the skin, and a threaded point 106, the part farthest from the
skin, respectively. The part nearest the skin comprises, at its
external end, a head 107 for turning the screw 103. The two end
parts are connected by a flexible middle part 108.
[0255] The middle part 108 is formed by an annular bellows 109
which connects the peripheries of the inner ends of the body 105
and the point 106. A flat elastic blade 110 also connects these two
ends, which blade contains their axis, thus allowing a relative
pivoting movement between the two parts 105 and 106 in a plane
perpendicular to the blade, while preventing such a movement in the
plane of the blade. The blade 110 thus forms a neutral axis in a
rotation between the parts 105 and 106 around an axis perpendicular
to the axis of these parts and contained in the plane of the blade
110.
[0256] Thus, the bellows 109 and the blade 10 delimit two chambers
111 and 1112 disposed on either side of the neutral axis. During a
bending of the screw, which causes a relative rotation of its parts
105 and 106 around the above-mentioned axis, the volume of one of
the chambers (111 in FIG. 6) increases while the volume of the
other (112) decreases.
[0257] The chambers 111 and 112, as well as their connecting
conduits as described above, are filled with a hydraulic fluid.
[0258] Borings 113 parallel to the axis of the screw each connect
to one of the chambers 111 and 112 and connect to one another
through a transverse boring 114. A valve 115 (not represented in
FIG. 6) mounted in the boring 114 makes it possible to open or
close the connection between the chambers 111 and 112, as well as
to regulate the cross-section of the passage between these
chambers.
[0259] The control rod 116 of the valve 115 is coaxial with the
body 105 of the screw, and its control head, which for example is
itself a screw, is included in the head 107 of the screw. Thus it
is disposed near the outside of the body of the patient where the
screw is inserted.
[0260] The screw 103 is position in a known way, but such that its
middle part 108 is disposed at the level of the fracture. Moreover,
the screw is immobilized in axial rotation in such a way that the
plane of the blade 110 is perpendicular to the plane of FIG. 2, in
a way that can produce a relative rotation of the parts 105 and 106
of the screw around an axis perpendicular to this plane and passing
through the level of the part 108.
[0261] During the implantation, the valve 115 is closed. Thus, no
connection is permitted between the chambers 111 and 112, so that
the screw is perfectly rigid throughout the time it takes for the
callus to form. Once the callus has formed, a minor intervention
allows access to the control head of the valve 115, making it
possible to open this valve, and to adjust its opening and
consequently the coefficient of resistance of the implant.
[0262] FIGS. 1a and 1b illustrate the utilization of a standard
shock-absorbing device. Generally, however, the shock-absorbing
devices used will be better adapted to the particular use to be
made of them.
[0263] Thus, FIG. 7 shows a shock-absorbing device in which each of
the two chambers 220 and 221 has a variable volume due to the
presence of a bellows 222 and 223, respectively.
[0264] The chamber 220 is formed of two semi-chambers in the shape
of cupels 224 and 225 whose openings face one another. These cupels
are connected by the bellows 222.
[0265] Likewise, the chamber 221 is formed of two semi-chambers,
one of which is constituted by a cylinder 226 welded to the outside
of the bottom 227 of the cupel 225, and the other of which is a
cupel 228 whose opening faces the cylinder 226. The cylinder 226
and the cupel 228 are connected by the bellows 223.
[0266] Each of the bellows in this case is embodied in the form of
a toric sector made of sheet metal welded along each of its edges
and the edges of the cupels 224 and 225, in the case of the bellows
222, and along the free edge of the cylinder 226 and the edge of
the cupel 228 in the case of the bellows 223.
[0267] The chambers 220 and 221 are filled with a hydraulic fluid
and connect through a calibrated opening 229 cut into the bottom
227 of the cupel 225 and opening into the cylinder 226. Thus, when
a compressive stress is exerted on the cupels 224 and 225 of the
chamber 220, tending to push them toward one another, the volume of
this chamber decreases while the fluid passes through the opening
229 and is forced into the chamber 221, whose volume increases. The
force which opposes the approach of the cupels 224 and 225 is
proportional to the approach speed, assuming that the bellows do
not exert any force, particularly of an elastic nature.
[0268] When the compression stress stops, the bellows return the
chambers 220 and 221 to their original configuration.
[0269] In the embodiment represented, the chamber 221 is housed in
a cylindrical stress-transmitting support skirt 230, welded to the
bottom 227 of the cupel 225 around the cylinder 226. In this case,
the stresses are transmitted to the shock-absorbing device by the
cupel 224 and the skirt 230, which two elements connect the two
parts of the implant.
[0270] In FIGS. 8 through 10, the cupel 224 comprises, in a
cylindrical area, an external threading 240 onto which is screwed a
stop ring 241 equipped with a cooperating internal threading. One
end of the ring 241 faces a shoulder 242 of the cupel 225, in this
case the edge of this cupel onto which one edge of the bellows 222
is welded.
[0271] Moreover, a beaded chain 243 is engaged in the annular space
244 delimited by the fold of the bellows 222, which includes the
edge of the cupel 224, and the bottom of the ring 241. The beads of
the chain in this case have a diameter substantially equal to the
distance at equilibrium between the edges of the cupels 224 and 225
which face one another. One end 245 of this chain exits the annular
space 244 through a slot 246 formed in the lateral wall of the stop
ring 241, opposite the shoulder 242.
[0272] During the insertion of the implant, and in the subsequent
consolidation phase, the chain 243 prevents the collapse of the
bellows 222 in such a way that, under compression, the device
behaves substantially like a traditional rigid implant. If the
chain has a diameter smaller than the thickness of the space 244,
the device has a partial shock-absorbing function in this
phase.
[0273] After consolidation, the chain 243 is removed by pulling on
its end 245, the device then functioning entirely according to the
shock-absorbing principal of the invention. However, a compression
limit is obtained by the abutment of the edge of the ring 241
against the shoulder 242 of the cupel 225. Thus, the device once
again functions, under compression, like a rigid implant.
[0274] FIGS. 11a and 11b illustrate an alternate embodiment of the
locking system of the chain 243 of FIGS. 8 through 10. In this case
an elastic needle 250 has one of its ends 251 welded to the inside
of the cupel 224 of the chamber 220. Initially, the other end 252
of the needle 250 is engaged in the calibrated opening 229, which
it obstructs. Due to the incompressibility of the hydraulic fluid
contained in the chambers of the device, the device is perfectly
rigid.
[0275] When desiring to make the device function according to the
invention, it suffices to distance the cupels 224 and 225 from one
another enough to disengage the end 252 of the needle 250 from the
opening 229. This opening is then free to allow the passage of the
hydraulic fluid and cannot in any case be re-blocked by the needle
250.
[0276] The rachidian implant 260 of FIG. 12 comprises two end parts
261 and 262 equipped with anchoring cones 263 and 264,
respectively. The part 261 also includes a sleeve 265 connected to
the anchoring cone by a length adjusting screw 266.
[0277] A shock-absorbing device 267, in this case the same type as
those described in reference to FIGS. 7 through 11, has a cupel 224
integral with the sleeve 265 and a skirt 230 integral with the end
part 262.
[0278] An implant of this type can be used during operations for
restoring the functioning or the integrity of the vertebral column.
The vertebrae at least partially retain their structural functions
in case of static stresses. On the other hand, the implant is more
active when the dynamic stresses are substantial.
[0279] FIG. 13 shows an arthrodesis of the vertebral column in
which two pins 301 and 302 are anchored in two vertebrae 303 and
304 so that, in a known way, they provide a connection between
these two vertebrae. The pins 301 and 302 in this case are each
embodied in two parts 301', 301" and 302', 302", respectively, each
of these parts being connected at one of its ends to one of the
vertebrae 303 and 304, and at its other end to the other part, by
means of a device 305 according to the invention.
[0280] An example of this type of device is described in reference
to FIGS. 14 and 15, respectively in cross-section and in axial
section.
[0281] The implant 305 comprises a shell constituted by two
half-shells 306 and 306' which are upper and lower shells,
respectively. Disposed inside this shell is an alveolar structure
307, particularly made of silicone, which ensures both the elastic
and shock-absorbing functions between the two half-shells 306 and
306'.
[0282] The structure 307 comprises an outer toric chamber 308 and a
substantially cylindrical central chamber 309, these two chambers
being separated by a partition 310. The partition 310 is
constituted in the following way.
[0283] It forms a thick wall 311 of low elasticity (of high elastic
rigidity) relative to the external wall 312 of the outer chamber
308. Radial conduits 313 disposed inside this wall 311 connect the
chambers 308 and 309. Annular chambers 314 which communicate freely
with one another are formed between the conduits 313, which
conduits 313 and chambers 314 are distributed in layers
perpendicular to the axis of the prosthesis.
[0284] The lower half-shell 306 in this case is connected by a
bellows 315 to base 316. Means, not represented, make it possible
to inject hydraulic fluid under pressure into the chamber 317
delimited by the bottom of the half-shell 306, the bellows 315 and
the base 316. It is thus possible to adjust the axial thickness of
the implant 305.
[0285] Obviously, a differential adjustment of the two bellows 315
makes it possible to realign the vertebrae of FIG. 13.
[0286] By providing a range of adjustment that is sufficient to
allow a substantial variation of the length of the device, it is
possible to produce and adjustable internal fixation, allowing the
repair of the vertebrae without the need for osseous fusion of the
joints of these vertebrae.
[0287] Other means which are not represented, but which are
included for most fluid injection sites or adjusting buttons
implanted under the skin of the patient, make it possible to adjust
the pressure in the chambers 308 and 309 on the one hand, and 314
on the other hand, the pressure at equilibrium in effect being
equal in the low-pressure chambers 308 and 309, and lower than the
pressure in the high-pressure chamber 314.
[0288] FIG. 14 also shows that the central low-pressure chamber 309
of each prosthesis 305 is connected to the high-pressure chamber of
the other prosthesis by conduits 318 equipped as described
below.
[0289] Mounted in each conduit 318 is an anti-return valve 319
which can open from a low-pressure chamber 309 into the
corresponding high-pressure chamber 314, when the pressure in the
chamber 309 becomes higher than that in the chamber 314. Moreover,
a pressure control valve 320 is mounted in parallel with the valve
319, which valve is calibrated in a known way to establish a
predetermined differential pressure between the low-pressure
chamber 309 and the high-pressure chamber 314.
[0290] It is noted that the conduits between the low-pressure
chambers could, in a variant, be disposed outside the shell. One
such embodiment would involve producing a conduit of this type at
least partially in the form of a catheter made of elastic material
surrounded by a substantially more rigid tube, the catheter and the
tube being joined into rings at their ends, for example by means of
adhesive bonding or welding. The high-pressure chamber in this case
is constituted by the volume between the catheter and the tube.
[0291] Refer now to FIG. 16, in which the same reference numbers
used in FIGS. 14 and 15 have been repeated, combined with the
letters D and G for the right and left implants, respectively (seen
from the rear of the patient wearing the prosthesis).
[0292] In FIG. 16, the various chambers are comparable to pressure
cylinders wherein the body constitutes the chamber itself. These
cylinder bodies are considered to be fixed, which means that the
lower parts 301' and 302' of the pins 301 and 302, the bases 316,
and the lower half-shells 306 are assumed to be fixed.
[0293] The pistons 309D' and 309G' and 314D' and 314G' illustrate
the stresses exerted on the corresponding chambers by the upper
half-shells 306' when the patient bends laterally, to the left in
FIG. 16 as seen from behind. As for the pressure cylinders 308D and
308G, the elasticity of the walls is only symbolized, by the
springs 321D and 321G, the pressure variations in the chambers 308
in practice resulting only in movements of fluid though the
conduits 313 due to this elasticity.
[0294] Finally, these conduits 313 are symbolized by flexible
restrictions compressed to a greater or lesser degree by the fluid
contained in the high-pressure chambers 314.
[0295] The behavior of the left implant, which is compressed during
the movement, will now be examined. Due to the thickness of the
wall 311 and thus its low elasticity, the central low-pressure
chamber 309 can increase in diameter only slightly to compensate
for the decrease in its height. The fluid it contains will then be
expelled through the conduits 313 to the peripheral low-pressure
chamber 308. Thus, the desired shock-absorbing function is
obtained.
[0296] Furthermore, the elasticity of the wall 312, symbolized by
the spring 321 of FIG. 16, will simultaneously have the tendency to
resist the expansion of the chamber 308, and therefore the entry of
the fluid into this chamber. Thus, the function of elastic
resistance is obtained.
[0297] It is noted that, as the left half-shells 306 and 306' move
closer together, the left high-pressure chambers 314 also move
closer to one another, which has the effect of increasing the
coefficient of resistance by reducing the cross-sections of the
conduits 313.
[0298] On the right side, where conversely, the half-shells 306 and
306' have a tendency to move apart, the fluid will move in the
opposite direction. Due to the rigidity of its walls, the
cross-section of the chamber 309 will not vary much. But as its
height, and therefore its volume, increases, fluid will enter it
from the chamber 308 through the conduits 313. The cross-sections
of the latter will increase, which will have the effect of reducing
the coefficient of resistance on this side, thus compensating for
its increase on the other side.
[0299] This elastic behavior will result from most of the stresses
exerted on the lateral wall of the chamber 309.
[0300] Consequently, it is noted that during the patient's
movement, the implant essentially sustains the high-amplitude or
high-speed stresses. But it is the bone graft which will sustain
the moderate static loads or loads resulting from relatively slow
movements. The result is a reduction in the risk of
osteoporosis.
[0301] It will now be seen, in reference to FIGS. 17a through 17d,
how the differential pressure between the high-pressure and
low-pressure chambers, which is essential for retaining the
shock-absorbing characteristics of the implant, is regulated. These
figures illustrate the pressure levels in the central low-pressure
chamber and the high pressure chambers as a function of time.
[0302] It is assumed, in reference to FIGS. 17a through 17d, that
the patient successively bends to his right rapidly (FIG. 17a), or
slowly (FIG. 17b), straightens himself (FIG. 17c), and bends again,
but to his left (FIG. 17d). The solid lines (HPD and BPD) relate to
the right implant, and the broken lines (HPG and BPG) relate to the
left implant.
[0303] During a rapid movement, a substantial pressure peak is
observed which is positive on the bent side, and negative on the
other side, in both the high-pressure and low-pressure chambers.
The reason why this occurs in the high-pressure chambers will be
explained below. In the low-pressure chambers, it is due to the
rigidity of the walls of the chambers 309 and the shock-absorbing
effect of the conduits 313, which slow the flow of fluid from the
chambers 309 to the chambers 308.
[0304] The time t.sub.1 that it takes for the patient to bend to
the right, during which the pressure levels vary, then stabilize,
can be seen in FIGS. 17a and 17b. The respective pressure levels
were substantially equal before the movement, by reason of
symmetry, but after the movement the pressure levels are obviously
higher on the right than on the left.
[0305] When the movement is rapid enough, there is a period t.sub.2
included in t, during which the pressure in the right low-pressure
chamber 309 becomes higher than the pressure in the left
high-pressure chamber 314. The anti-return valve 319G then opens
and allows the passage of fluid from the right low-pressure
chambers to the left high-pressure chamber. Simultaneously, the
pressure control valve 320G allows a flow in the opposite direction
so as to prevent the differential pressure between the high and low
pressure from exceeding the set-point value.
[0306] Thus, if need be for any reason, the differential pressure
predetermined by the calibration value of the pressure control
valve is re-established. This can occur continuously in the case of
leaks from the high-pressure chambers to the low-pressure chambers,
or when the low-pressure chambers are refilled by injection, or
even when an adjustment is made to increase the differential
pressure between the high and low pressure. The device then
functions like a pump controlled by the movements of the
patient.
[0307] If, on the other hand, the bending movement is slow, as
shown in FIG. 17b, the fluid has the time to flow from the right
low-pressure chambers 309 to 308 without causing excessively high
pressure levels. The anti-return valve 319G does not open.
[0308] When the patient straightens, the pressure levels change as
shown in FIG. 17c. Given that the pressure levels on the right side
are initially higher than those on the left side, it is not very
probable that during the period t.sub.3 of the movement the
prevailing low pressure in the left chamber 309 will become greater
than the prevailing high pressure in the right chamber 314.
[0309] It is only when the patient bends quickly enough to the
left, as represented in FIG. 17d, which is symmetrical to the case
in FIG. 17a, that the differential pressure between the right
high-pressure chamber and the left low-pressure chamber
re-establishes its set-point value. The period t.sub.4 of the
movement, and the period t.sub.5 during which the left low pressure
becomes greater than the right high pressure, as shown in this
figure.
[0310] It is understood that what has just been described
step-by-step in reference to FIGS. 17a through 17d actually occurs
continuously when the patient is moving normally, successively
adopting various natural postures. Consequently, it is noted that
this results in a continual biochemical adaptation of the implants
to the stresses imposed on it by the patient.
[0311] In light of the auto-refill principle explained in reference
to FIGS. 17a through 17d, it may be seen that the pressure points
that are too acute will flatten out due to the fact that the fluid
is laminated as it flows into the anti-return valve. This produces
an additional shock-absorbing effect when the cell is stressed
suddenly enough that the low pressure surpasses the high pressure.
Taking into account the variability of the coefficient of
resistance as a function of the loads, as described above, this
proves to be a device endowed with an advantageous capacity for
self-adjustment.
[0312] Another advantage of this mode of functioning resides in the
fact that a practically continuous circulation of fluid occurs in
the hydraulic circuit of the implant of the invention. This
circulation avoids the risk of collapse and thus limits the need
for maintenance operations.
[0313] Another embodiment 322 of the implants 305 is seen in FIGS.
18 through 22.
[0314] The implant 322 is again embodied in the form of an alveolar
structure made of elastomer contained in a shell composed of a
lower half-shell 323 and an upper half shell 324.
[0315] The alveolar structure of this embodiment is in the shape of
a disk and forms three low-pressure chambers 325 in the form of
sectors, distributed substantially equally around the axis of the
disk, at 120.degree. from one another. The three chambers 325
connect through a network of calibrated conduits 326, here disposed
in two transverse layers.
[0316] Three groups of high-pressure chambers 327, which
communicate with one another by any appropriate means, are disposed
between the low-pressure chambers 325. The chambers 327 are flat in
shape, and each group has three of them, interposed between the
layers of conduits 326. The pressure in the high-pressure chambers
determines the cross-section of the conduits 326 and thus their
characteristics of viscosity.
[0317] FIG. 22 shows that the low-pressure chambers are connected
to the high-pressure chambers by a set of anti-return valves and
pressure control valves. Each low-pressure chamber 325 is connected
to the high-pressure chamber 327 that is diametrically opposed to
it by an anti-return valve 328 which opens in the direction from
the chamber 325 to the chamber 327, in parallel with a pressure
control valve 329.
[0318] In this case, there is no intersection, as in the embodiment
of FIGS. 14 and 15, and as symbolized in FIG. 17, of the
connections between the low-pressure and high-pressure chambers of
two implants mounted in parallel. Moreover, there is only one type
of low-pressure chamber.
[0319] During an axial compression, the fluid contained in the
conduits 326 is, due to the thickness of the walls of the latter,
expelled to the chambers 325 with a viscous fluid behavior. The
walls of these chambers are then forced toward the outside, giving
the implant its elastic behavior. In this respect, this implant
behaves like the one in the preceding embodiment.
[0320] On the other hand, this implant has a particular behavior
relative to non-axial loads. For example, in the case of a load
exerted from the left side of FIG. 22, the low-pressure chamber
325a will be compressed, while the chambers 325b and 325c will be
at low pressure. The wall of the chamber 325a will then expand,
while part of the fluid contained in this chamber will flow into
the chambers 325b and 325c through the conduits 326, further drawn
by the prevailing low pressure in these chambers.
[0321] When the movement is large enough and rapid enough, the
outer wall of the low-pressure chamber 325a comes into contact with
the shell. The elastic behavior of the implant is then blocked, so
that the pressure rises sharply in the low-pressure chamber 325a.
This pressure can then become greater than the prevailing pressure
in the high-pressure chamber 327a which faces it, engaging the
process for regulating the differential pressure described above in
reference to the preceding embodiment.
[0322] An implant according to this second embodiment could
therefore be used alone, while retaining the differential pressure
regulation function.
[0323] Various implantations other than that represented and
described in reference to FIG. 13 can be envisaged for the implants
just described.
[0324] FIG. 23 shows a bone graft 330 disposed between two
vertebrae 331. Two implants 305 such as those in FIGS. 14 and 15
have been placed in the graft, symmetrically relative to the median
plane of the patient's body. The interconnections between the
implants and the functional principles are the same as those
described in reference to FIGS. 14 through 17.
[0325] FIG. 24 shows a single implant 332 as described in reference
to FIGS. 18 through 22, implanted in a graft 333, which is itself
disposed between two vertebrae 334. A solution of this type ensures
good performance with regard to lateral as well as frontal
flexions.
[0326] Articulated implants embodied according to the invention
will now be described.
[0327] FIG. 25 shows an implant, or intervertebral prosthesis 400
intended to be disposed, as shown in FIG. 26, between two vertebrae
401, in place of an intervertebral disk. This implant must
therefore allow certain movements between the vertebrae 401,
contrary to what occurs in the case of an arthrodesis.
[0328] The implant 400 is generally formed by a shell comprising a
bottom 402 and a cover 403. The cover 403 rests on the bottom 402
as a result of two spherical surfaces with the same radius, the
surface 404 of the bottom which faces upward and the surface 405 of
the cover which faces downward. Thus, the cover 403 can pivot
relative to the bottom 402 around three axes.
[0329] The bottom 402 is hollow, so as to define a space 406 inside
the implant. The cover 403 forms a projection 407 into this space,
the end of which projection is connected to the bottom by three
inner viscoelastic "ligaments" 408, which will now be described in
reference to FIG. 27.
[0330] Each ligament 408 comprises a rigid hollow body 409 which is
substantially cylindrical and has, at one of its ends, an opening
to the ambient air 410. This opening is sealed by an ampulla, or
elastic bellows 411. The bellows 411 is a cylinder closed at its
end opposite the opening 410 by a bottom 412, and its lateral wall
forms a helical fold 413 with a variable pitch which increases from
the opening 410 to the bottom 412.
[0331] The body 409 and the bellows 411 delimit a chamber 414
containing a hydraulic fluid which is supplied from, and whose
pressure can be regulated by, a conduit 415 and a valve 416.
[0332] At the other end of the body 409, the base 417 of this body
supports an annular cylindrical chamber 418 whose inner wall 419
and outer wall 420 are also constituted by bellows. The chamber 418
contains a hydraulic fluid which is supplied from, and whose
pressure is regulated by, a conduit 421 and a valve 422.
[0333] At the center of the annular chamber 418, the wall of
another cylindrical chamber 423 is formed by a bellows 424. The
chamber 423 connects to the chamber 414 through a calibrated
opening 425 cut into the base 417 of the body 409. The chamber 423
is therefore supplied and pressurized from the chamber 414.
[0334] The end of the bellows 424 opposite the base 417 is sealed
by a plate 426 which carries a support piece 427 passing through an
opening 428 of an end plate 429 of the annular chamber 418. The end
plates 426 and 429 are integral.
[0335] Formed inside the chamber 423 is a chamber 430 mounted on
the base 417 of the body 409 by means of posts 431. One of these
posts 431 is hollow and makes it possible to supply and to
pressurize the chamber 430 with hydraulic fluid from a conduit 432
and a valve 433.
[0336] The wall of the chamber 430, between the junction points of
the posts 431 and the base 417, forms a bellows 434. The bottom of
the chamber 430, which faces the base 417 of the body 409, carries
a needle 435 which penetrates into the calibrated opening 425.
[0337] The implant is anchored at the projection 407 and at the
bottom 402 by its elements 409 and 427.
[0338] It is easily understood that the length of the ligament 408
is a function of the pressure in the annular chamber 418, which
determines the elongation of the bellows 419 and 420. This length
can be adjusted by means of the valve 422.
[0339] Moreover, the coefficient of resistance of the ligament 408
is a function of the free cross-section of the calibrated opening
425, and thus of the penetration depth of the needle 435. This
coefficient can be adjusted by means of the valve 433.
[0340] Finally, with regard to its elasticity, the bellows is
comparable to a helical spring with a variable pitch which becomes
increasingly steep as it is compressed and its spires progressively
come into contact. This bellows determines the elasticity of the
ligament 408 since, when the latter is compressed, it elastically
opposes the penetration of the hydraulic fluid into the chamber 414
through the opening 425. The coefficient of elasticity can
therefore be adjusted by means of the valve 416 by pre-compressing
the bellows 411 to a greater or lesser degree.
[0341] It is noted that a structure similar to that of the ligament
just described could be used in place of the device of FIG. 7, in
order to render its various functions adjustable.
[0342] An alveolar structure 500 made of elastomer which could
replace the three ligaments 408 of FIG. 25 will now be described in
reference to FIGS. 28 through 31.
[0343] This structure is practically identical to that of the
implant 322 of FIGS. 18 through 21 (FIG. 28 has been schematized).
It is noted, however, that in this case the structure 500 has an
opening 501 of triangular section for receiving a projection of the
cover, similar to the projection 407 and intended to form a pivot
between the bottom and the cover of the prosthesis.
[0344] The interconnections between chambers are the same as in the
case of the implant 322, and the functioning of the present
prosthesis and the implant are the same from the hydraulic
standpoint.
[0345] The differences reside in the way in which the stresses are
applied. In this case, essentially transverse stresses are applied
to the low-pressure chamber 502 by the projection of the cover.
[0346] FIG. 32 shows one possible implantation of the prostheses of
FIGS. 25 through 31.
[0347] This figure shows the bottom 503 and the cover 504 of the
prosthesis. The bottom 503 is equipped with fittings 505 and the
cover 504 with fittings 506 for their respective attachment to a
lower vertebra 507 and an upper vertebra not represented.
[0348] The various hydraulic chambers are connected by conduits 508
to a set of subcutaneous control buttons 509, particularly
push-buttons, disposed behind the vertebrae. Safety devices are
preferably provided in order to prevent ill-timed operation of the
buttons. In a variant, fully hydraulic adjustment means could be
provided, with a subcutaneous access site connected to the various
chambers by a slide valve.
[0349] FIGS. 33 and 34 show, in partial perspective and in
cross-section, respectively, an anti-return valve which can be used
in the invention.
[0350] This valve is composed of a conduit 510 connected to the
high-pressure and a conduit 511 connected to the low pressure.
These conduits are coaxial, and the end of the low-pressure conduit
511 is engaged inside the end of the high-pressure conduit 510. The
end of the conduit 511 inside the conduit 510 is flat.
[0351] As long as the high pressure is greater than the low
pressure, the end of the conduit 511 remains flat and the valve
remains closed, thus preventing the possibility of a flow from the
conduit 511 to the conduit 510. But when the low pressure becomes
higher than the high pressure, the end of the conduit 511 opens and
fluid flows from the conduit 511 to the conduit 510.
[0352] Finally, FIGS. 35 through 39 illustrate a coxofemoral
prosthesis embodied according to the principles of the
invention.
[0353] This prosthesis is intended to be used after a fracture of
the neck of the femur and resection of its upper part. It comprises
a pin 600, one end of which is intended to be attached to the
remaining part of the femur, and a hollow sphere 601 whose wall
includes an opening 602 to allow it to be penetrated by the other
end of the pin 600.
[0354] The upper end of the pin 600, inside the sphere 601, is
integral with a cylindrical head 603. The latter is capable of
sliding and forming a piston in a circular opening 604 of an
internal partition 605 of the sphere. The axis of the head 603 and
of the opening 604 passes substantially through the other end of
the femur, at the level of the knee joint.
[0355] The partition 605, along with tbs piston 603, delimits
inside the sphere two chambers 606 and 607, which are respectively
upper and lower chambers. The chambers 606 and 607 contain
viscoelastic devices which determine the relative movement of the
pin 600 and the sphere 601, as a function of the stresses
applied.
[0356] In one particularly simple embodiment, these viscoelastic
devices can be simply constituted by an elastic foam which fills
the chambers 606 and 607, and a calibrated opening formed in the
head 603. The foam contains a hydraulic fluid and an appropriate
joint is disposed at the level of the opening 602.
[0357] However, the embodiment in FIGS. 38 and 39 is preferred.
[0358] In this case, the viscoelastic devices 608 are embodied is a
form practically identical to that of the structures 307 in the
implants 305. The difference resides in the fact that the
structures 307 are generally of cylindrical shape, while the
devices 608 have a shape which is generally hemispherical. But in a
similar way, they are chiefly composed of a peripheral low-pressure
chamber 609 and a center low-pressure chamber 610, separated by a
wall 611.
[0359] Annular high-pressure chambers 612 formed within the
thickness of the wall 611, are interposed with calibrated conduits
613 which connect the low-pressure chambers 609 and 610. The
intersecting interconnections between chambers are embodied as
above.
[0360] When the prosthesis is stressed, the head 603 compresses one
of the devices 608, while the other device is at low pressure.
Everything indicated relative to the functioning of the twin
implants 305 remains valid in the present case.
[0361] It is noted that in this case, when a device 608 is
compressed, its line of tangency with the inner surface of the
sphere moves closer to the partition 605. The elastic outer wall
surface then decreases, which has the effect of increasing the
elastic rigidity of the device.
[0362] The interconnections between chambers are embodied as shown
in FIG. 39, by borings 614 formed in the head 603 and in the pin
600. These borings emerge at the level of a control button box 615
(FIGS. 35 and 36). This box is disposed subcutaneously so as to be
easily accessible, in order to allow the necessary adjustments.
[0363] The implant 700 of FIG. 40 generally comprises a
viscoelastic cell 701, for example like that is the implant 305 of
FIG. 13 and the subsequent figures, or like the ligament 408 of
FIG. 27, as well as a distance adjusting element 702, in this case
for adjusting the height, and a refill cell 703. These elements are
mechanically disposed in series, in support, with the half-pins
704, 704' of the arthrodesis, which can belong to the two vertical
members of a frame. The half-pins 704, 704' consequently support
the pressure of the patient's body, which is variable as a function
of his posture.
[0364] The adjusting element 702 can be embodied as shown in FIGS.
41 and 42, in the form of an expandable toric bellows, which can
expand axially. Its central free space allows it to house a
protuberance of the viscoelastic cell.
[0365] In a variant, the adjusting element can be is the form of
the disk-shaped bellows 702' of FIGS. 43 and 44.
[0366] The adjusting element 702 (or 702') can be connected by a
conduit 705 to a tube valve 706 which can itself be connected to a
pump 707. Thus, it is possible to adjust the thickness of the
element 702. It is therefore possible to adjust not only the total
length of the prosthesis, but also the angle formed between its
upper part (the half-pins 704) and its lower part (the half-pins
704') by means of a differential filling of two elements 702 of the
prosthesis.
[0367] It is noted that the valve 706 itself can be implanted, in
which case it is accessed either by cutaneous incision or by means
of an access site, or external, the conduit 705 being
transcutaneous.
[0368] In another embodiment, represented in FIG. 46, the filling
of the adjusting elements is carried out with the aid of a high
pressure reservoir 708, in this case dilatable, and a slide valve
709. In a similar way, the emptying of these elements occurs into a
low-pressure drainage collector 710, also dilatable, through
another slide valve 711 (or in the same way, through a three-way
valve).
[0369] Moreover, a filling valve 712 makes it possible to fill the
reservoir 708, and a drainage valve 713 makes it possible to empty
the reservoir 710. The reservoirs 708 and 710 are implanted and the
valves 712 and 713 can be external or implanted, as in the case of
the valve 706. Generally, however, they will be implanted, since
their access should be far less frequent than that of the valve
706.
[0370] The refill cells 703, whose function will be described
below, are entirely similar to the adjusting elements 702. However,
they are connected to the high-pressure and low-pressure reservoirs
708 and 710 not by slide valves, but by anti-return valves 714 and
715, respectively. The anti-return valves 714 are connected from
the cells 703 to the high-pressure reservoir 708, and the
anti-return valves 715 are connected from the low-pressure
reservoir 710 to the cells 703.
[0371] The cells 703 serve as pumps for refilling the high pressure
reservoir 708. In effect, when the patient bends, for example to
the right, the cell 703D is compressed. When the pressure in this
cell surpasses the pressure in the reservoir 708, the anti-return
valve 714D
[0372] opens and fluid passes from the cell 703 to the reservoir
708. Simultaneously, the left cell 703G draws in fluid from the
low-pressure reservoir 710.
[0373] A pressure control valve 716 prevents the high-pressure from
exceeding a predetermined value.
[0374] It is noted that if only angular corrections are desired,
the refill device can be greatly simplified, and the refill cells
in particular can be eliminated. In effect, in this case it
suffices to connect the adjusting elements by means of a slide
valve. When the patient bends, for example to the right, the valve
is opened so that fluid passes from right to left, then is closed
again. When the patient straightens, the height of the left side
will be larger and that of the right side will be smaller.
[0375] The viscoelastic cells have not been described is this
embodiment. It is simply noted that in the case where they comprise
high-pressure chambers, like for example the implants 305 or the
ligaments 408, those chambers can be connected to the high-pressure
reservoir 708 by a valve, for example a slide valve. Thus it is
possible to easily rigidify the viscous behavior of these cells.
The low-pressure chambers of the viscoelastic cells, for their
part, can also be connected to the low-pressure reservoir 710.
[0376] FIG. 48 shows a possible implantation for the elements just
described. The connecting conduits generally have the reference
number 717. It is noted that all these elements can have very small
dimensions, and the hydraulic volumes can be very low.
[0377] The physical characteristics of the implants just described
can be modified postoperatively by any means, including entirely
non-invasive means, whether in terms of their viscoelastic
properties, their dimensions, their lateral or antero-posterior
inclination, or their anti-rotational resistance.
[0378] By way of example, FIG. 49 illustrates an electronic control
circuit for an implant of the type represented in FIG. 47.
[0379] This circuit is embodied in two parts, an extracorporeal
part 720 and an implanted part 721. These two parts are in contact
by means of two antennas 722 and 723, respectively.
[0380] The circuit part 720 comprises a power supply 724, a remote
control device 725, a detection and amplification module 726, and a
monitor 727. The remote control device 725 controls a radio
frequency multiplexer 728 connected to the antenna 722.
[0381] The circuit part 721 also comprises a radio frequency
multiplexer 729 connected to the antenna 723. The multiplexer 729
is connected to a radio frequency/D.C. voltage converter 730 which
supplies electric power to the other modules of the circuit part
721, namely a radio frequency oscillator 731 and sensors 732, as
well as actuators 733.
[0382] In the case of FIGS. 40 and 47, the sensors 732 can be, in
particular, pressure sensors in the distance control elements 702,
and possibly in the chambers of the viscoelastic cells 701. The
actuators can comprise electrically operated valves such as the
slide valves 709 and 711. More particularly, the pressure sensors
can comprise, for each side of the patient, one sensor for each
low-pressure chamber and one sensor for the high-pressure chamber.
Pressure sensors can also be provided on the means for attaching
the implants, such as screws or hooks, as well as on the bone,
possibly bridged.
[0383] When the doctor wishes to know and possibly to adjust the
pressure in the elements 702, for example, he operates the remote
control device 725. The antenna 722, placed in proximity to the
antenna 723, emits a code that is detected and used by the
implanted part 721. Moreover, the radio frequency is transformed
into a D.C. supply voltage for the sensors 732, the oscillator 731,
and the multiplexer 729. The implanted part then in turn emits a
code containing the pressure information, which is detected and
displayed on the monitor 727. The adjustment of the elements 702 by
means of the electrically-controlled valves 733 occurs in the same
way.
[0384] It is noted that thanks to the invention, it is possible to
perform a detailed examination of the behavior of the implants. For
example, in the case of a vertebral implant, it is possible to
measure its frequency response, or its impulse response, by having
the patient sit on a seat equipped with means for moving in any
direction desired, and by recording the response of the pressure
sensors. The adjustment of the various stationary pressure levels
can thus be determined with great precision.
[0385] It is noted that as implant according to the invention can
include analgesic neurostimulating means of a known type, as well
as a programmable medication delivery pump.
[0386] Generally, for all of the implants described above which do
not have remote control by means of radio frequencies or the like,
devices are provided which are accessible either directly, as in
the case of subcutaneous buttons, or by means of a benign
intervention. The means for adjusting by remote control without
physical contact can be rotary valves of the "sluice" type which
are multidirectional, whose rotation is induced by an external
rotating magnetic field. A spiral spring re-establishes the
equilibrium in the closed position. It is advantageous to be able
to carry out the desired adjustments relatively often, either in a
planned way, for example in order to progressively reduce the
coefficient of resistance as a graft consolidates, or as necessary,
for example in order to relieve pain.
[0387] Likewise, all of the above-mentioned implants can be
provided with improvements which have only been described in
reference to certain embodiments. This is the case, for example,
with the dimensional adaptation provided in the implants of FIGS.
14 and 27. A disposition of this type is particularly useful in any
implant intended for a child who is still growing, or an elderly
person whose size is gradually decreasing.
[0388] In FIGS. 50 to 59 which follow, it is assumed that the spine
extends in a vertical direction and that the two individual
implants are arranged on either side of the succession of spinous
processes, and that the lower pedicle screws are screwed into a
first vertebra and the upper pedicle screws are screwed into
another vertebra, which may or may not be adjacent and is arranged
above the first one. The two individual elements are shown in a
frontal plane which is the plane of the drawing. The result of this
is that the pedicle screws should be oriented in a more or less
sagittal plane, in other words more or less perpendicular to the
plane of the drawing, or at any rate inclined, but for reasons of
simplicity of representation they have been shown in the same
frontal plane. Likewise, the joining elements have been shown in
the same frontal plane, whereas they should be in the perpendicular
or inclined plane which contains the pedicle screws.
[0389] FIG. 50 shows two individual implants, a right-hand one and
a left-hand one, generally designated by 1' and comprising a lower
end rod 2' and an upper end rod 3' between which there is
interposed a deformable hydraulic element 4' which has been shown
in the form of a cylinder/piston assembly, but which in reality
would instead be in the form of a metal bellows so as to prevent
the escape of hydraulic liquid. Alternatively, this deformable
element can be of the telescopic type or of an otherwise deformable
type, for example a cylindrical cell which is elastic
longitudinally but not transversely. The rods 2' and 3' are guided
in the continuation of one another so as to move along the same
vertical axis and to take up distanced or close positions as a
function of the extent of filling of the deformable element 4'. The
lower and upper ends 2', 3' have attachment means 5', 6' in the
form of articulations. Extending parallel to the element 1' there
is a rigid joining rod 7' which terminates in lower 8' and upper 9'
attachment means in the form of articulations. The rod 7' extends
essentially parallel to the individual element 1', but it could be
more inclined, and can be made integral with this element, although
this is not a requirement. Connected to each element 1' there is a
lower pedicle screw 10' and an upper pedicle screw 11' whose
threaded parts are fixed in the corresponding vertebral pedicles.
The posterior end of the pedicle screws 10', 11' is received in the
ends 5' and 6' in the manner of an articulation permitting an
angular clearance at least in the plane constituted by the element
1' and the joining element 7'. If appropriate, the articulation can
have a supplementary degree of freedom or can be of spherical shape
giving a degree of freedom in rotation in all directions.
[0390] In an intermediate position, the screws 10', 11' are fixed
and articulated respectively on the ends 8' and 9' of the joining
element 7' by articulations also permitting an angular clearance in
the common plane, for example the sagittal plane, of the element 1'
and of its joining element 7'.
[0391] The two deformable elements 4' of the pair of individual
implants which form the complex implant shown in the drawing are
connected via a line 12' on which there is arranged a hydraulic
circuit element 13', shown in the example in the form of a slide
valve.
[0392] The configuration shown in FIG. 50 permits antisymmetrical
rotation movements of the pedicle screws.
[0393] It is assumed that the pedicle screws have been screwed in
the angular positions shown on the drawing, that the hydraulic
circuits and the elements 4' are entirely filled with hydraulic
liquid and that the valve 13' is in the closed position. In such a
situation, the pedicle screws are blocked in their angular position
shown on the drawing. In this position, the internal volume of the
left-hand element 4' is smaller than that of the right-hand element
4', which corresponds to a more closed angle. If the valve is now
opened, it will be appreciated that the pedicle screws are going to
be able to pivot about the center of articulation of the points 8'
and 9' at the end of the joining rod, as a function of the increase
or reduction in the length of the corresponding element 1', itself
dictated by the volume of liquid present in the associated
deformable element 4'. Given the communication 12' between the two
deformable elements 4', it will also be appreciated that any
variation in the volume of liquid of one of the elements is
compensated by an inverse variation in the volume of the other in
such a way that the rotation of the pedicle screws in one direction
on one of the elements is translated into a rotation of the pedicle
screws in the other direction and having essentially the same
absolute angular value.
[0394] This property can be made use of in various applications
described in the above-mentioned EP and US applications.
[0395] If the hydraulic circuit element 13' is a viscoelastic
regulating element which considerably brakes the passage of liquid,
or prohibits this in the event of an abrupt angular movement of the
pedicle screws, the vertebrae can be left free to pivot relative to
one another in the frontal plane of the spine when the movements
are slow, and, by contrast, the screws can be immobilized or their
rotation considerably braked when the movements have a tendency to
be rapid. In this way it is possible to obtain a damping effect in
rotation while at the same time permitting a freedom of rotation
for slow movements.
[0396] If the element 13' is an element with which it is possible
to impose the supply of the hydraulic liquid into one of the
deformable elements 4' and the withdrawal of the same volume of
liquid from the other element 4', this supply then being followed
by a closure of the communication, it is possible, some time after
having implanted the two individual implants with given angles of
pedicle screws, to initiate an external command, for example a
transcutaneous magnetic command, in order to modify the angle and
thereby to effect in small stages a correction of a vertebral
deformation.
[0397] Means can be provided for exerting a continuous or
intermittent constant pressure in the bellows 4' in such a way as
to permanently stress the skeletal parts whose position is to be
corrected.
[0398] Of course, by using different hydraulic circuits, it is
possible to achieve the two functions which have been described, as
has been explained in the abovementioned applications.
[0399] Of course, according to the invention, it is also possible
to use each individual implant with its joining rod as a totally
independent element and to control each of the elements separately
without any interconnection 12', in order to ensure some or all of
the functions of modification of length and thus of angulation, as
well as viscoelastic damping.
[0400] In a preferred manner, the implant element is also combined
with a device with which it is possible to supply a deformable
element 4' with high-pressure liquid, if this is necessary, from a
deformable bellows functioning, for example, as a pump actuated by
the body, as has been described by the abovementioned application.
In the case of the use of two individual implants for forming a
complex implant, as shown, this supply and discharge means can be
common to both implants.
[0401] FIG. 51 shows a complex implant similar to that already
described herein, but in which the joining rods 7' are articulated
at the free ends or heads of the pedicle screws while the
deformable individual element is articulated in the intermediate
position, this giving an inversion of the movement of rotation
relative to that shown in FIG. 50, and additionally moves the
center of rotation of each pedicle screw rearwards.
[0402] FIG. 52 shows a complex implant which is identical, for the
individual implants 1', to that shown in FIG. 2. By contrast, the
joining element 7', which was a single rigid rod, has been replaced
by a joining element 14' formed in the manner of an individual
implant and thus comprising two ends 15', 16' which are capable of
moving longitudinally relative to one another with interposition of
a deformable hydraulic element 17', by which means it is possible
to have a joining element whose length can be modified if necessary
or which can itself have a damping effect analogous to that of the
actual implant 1 if this function is present.
[0403] Preferably, the two elements 17' of the two individual
implants shown are connected via a channel 18' with interposition
of a hydraulic circuit element 19'.
[0404] The desired functions will then be determined by the nature
and control of the hydraulic regulating elements 13' and 19' and it
will be appreciated that in such a design it is possible, if so
desired, to make the implant element 1' and its joining element 14'
interchangeable and thus to fix the center of rotation of the
pedicle screw either at the end 5' (or 6') or at the end 8' (or 9')
or even at another point between these articulations.
[0405] FIG. 53 is a diagrammatic representation of a practical
embodiment of the device in FIG. 52 (on which the lines and the
hydraulic circuit elements 13', 17' are not shown). The individual
implant shown includes a hydraulic bellows 4' bearing on its upper
face a component with an arm forming the rod 3', on its lower face
a plate with an arm 2' forming the lower rod, the said rods having
articulations 5' and 6' for the pedicle screws 10', 11'. The
element 14' includes a hydraulic bellows 17' whose lower plate
bears an arm 15' and the upper end an arm 16', the said arms
bearing, at their free end, the articulations 8', 9' receiving the
posterior ends of the screws 10', 11'. If appropriate, one arm of
the element 1' and another arm of the element 14' can be
mechanically secured or, by contrast, all these elements can be
left independent, the link then being made only by the screws 10',
11'.
[0406] Thus, it is possible to arrange the bellows spatially one
below the other and to form an implant according to the invention
with a greatly reduced size.
[0407] In FIG. 54, now, a device has been shown which is analogous
to that in FIG. 1, the only difference being that one of the
deformable devices or bellows 4' has been replaced by a deformable
device 20', which. furthermore can also be made in the form of a
bellows and in which the points of attachment of the lower 2' and
upper 3' arms have been inverted, in such a way that an increase in
the volume of the device 20' entails, in contrast to the increase
in volume of the device 4', a shortening of the implant element
instead of a lengthening.
[0408] It is thus possible, by virtue of the interconnection via
the line 12' and the element 13', to obtain symmetrical rotation
movements instead of antisymmetrical rotation movements. In other
words, the rotations of the screws 10', 11' on the right-hand side
of the spine are identical to the rotations of the screws of the
left-hand element, and of the same direction.
[0409] It is thus possible to obtain movements of flexion or
extension of the spine this time in the sagittal plane.
[0410] As in the other cases, this can be made use of either to
provoke a lordosis effect or vice versa, depending on the desired
aim, for example by acting in stages from an external command, or
to achieve a perfectly symmetrical damping effect in the case of
spontaneous movement of rotation between the vertebrae, or else to
achieve the two functions simultaneously by virtue of more complex
circuits.
[0411] FIG. 55 shows a configuration according to FIG. 54, but in
which the joining elements 7' are arranged, as in FIG. 2, in such a
way that the center of rotation of the pedicle screws is arranged
at the ends of the screws.
[0412] Alternatively, it is also possible to combine the solution
of FIG. 50 and of FIG. 51, placing the element according to FIG. 1
on the right of the spine, for example, and an individual element
according to FIG. 2 on the left, it being understood that in this
case the angular variations of the right-hand screws will at all
times be the inverse of those of the left-hand screws, but of more
different absolute value.
[0413] FIG. 56 shows a complex implant which also permits
symmetrical relations in the sagittal plane, as indicated in FIG.
55, but in which the joining rod 7' of each of the individual
implants has been replaced by joining elements which are themselves
of variable length, the one on the left being a joining element 14'
as shown in FIG. 52, while the joining element on the right also
has an inversion of action in the area of the bellows. In other
words, an arrangement is obtained in which the movements of
rotation on left and right are symmetrical in the sagittal
plane.
[0414] FIG. 57 is a diagrammatic representation of an embodiment
analogous to FIG. 53, but in which it will be seen that, by
inverting the bellow ends on which the arms are fixed, a movement
is obtained in the opposite direction to that in FIG. 53.
[0415] Referring to FIG. 58, this shows an assembly of two
individual implants, of which the left-hand implant includes two
end pieces 21', 22' which are able to move in the continuation of
one another, with interposition of a deformable element 23'
analogous to the deformable element 4'. The ends 24' and 25' of the
pieces 21', 22' have fixation holes enabling anchoring means, for
example pedicle screws to be secured. In contrast to the
representations in the
[0416] preceding figures, these fixation means at the ends 24', 25'
do not necessarily permit a pivoting of the pedicle screws, such as
the screws 10' and 11', and by contrast they can be formed by bores
or eyelets which permit rigid connection without any possibility of
pivoting of the screw relative to its corresponding end 24' or
25'.
[0417] The right-hand implant 26' also has two end pieces arranged
in the continuation of one another, namely 27' and 28', of which
the ends 29' and 30' are analogous to the ends 24' and 25' so as to
receive the pedicle screws without any possibility of movement of
the screw relative to the end which bears it. The end piece 27'
has, starting from the end 29', a part in the form of an elongate
threaded rod which terminates in the movable part of a deformable
hydraulic element 32' analogous to the element 23' or to the
element 4'. It will thus be appreciated that if the deformable
element 32' deforms and provokes a relative movement, for example
of spacing apart or distraction, between the pieces 27' and 28',
the movement of the piece 27' relative to the piece 28' will
provoke the rotation of the piece 27' on account of the fact that
its threaded rod moves in the fixed nut 31'. The result of this is
that the end 29' is driven relative to the end 30' in a
displacement movement simultaneously of translation and rotation.
Consequently, the end of the pedicle screw (not shown) borne by the
piece 29' of the movable piece 27' will describe a helical movement
whose axis is formed by the alignment of the pieces 27' and
28'.
[0418] If the two elements 20' and 26' are connected as is shown in
the figure, by a valve 13' in a line 12', it will be appreciated
that, as in FIG. 50, the reduction in the volume of the movable
element 23' will translate into an increase in the volume of the
movable element 32' and, thus, of the opposed axial displacements
of the implants, with, in addition, the movement of rotation of the
piece 27'.
[0419] Reference is now made to FIG. 59. In this figure, the
element 23' is identical to that in FIG. 58. Like the implant 26',
the other implant 33' has an end piece 28' terminating in an end
30' which permits the fixation and blocking of an anchoring screw.
By contrast, the element 33' includes a second end piece 34' with
its end 35' for receiving and blocking the anchoring screws, this
piece 34' being connected to the element 28' in such a way as to be
immobilized in translation but free in rotation about the axis of
the piece 34'. The movable part 36' of the deformable element 39'
has a piece in the form of a tapped nut 37' through which a
threaded part 38' of the piece 34' passes. It will thus be
appreciated that when the deformable element 39' deforms, the
movement of the movable piece 36' will provoke a rotation of the
end piece 34' about its axis, but without translation relative to
the end piece 28', in such a way that the end 35' turns without
displacement in translation relative to the end 30'.
[0420] In the embodiment shown in FIG. 59, by virtue of the valve
13', a variation in the volume of the deformable element 20' will
translate into an inverse variation in the volume of the deformable
element 39', in such a way that the lengthening of the element 20'
translates into a rotation of the end 35' in one direction, whilst
the shortening of the element 20' produces a rotation of the end
35' in the opposite direction.
[0421] Of course, all the other control combinations can be
realized, for example in the case of FIG. 58, in order to provoke
identical lengthening of the elements 23' and 32' while ensuring
the rotation of the piece 27'.
[0422] Referring to FIGS. 60 and 61, embodiments of the implant 26'
in FIG. 58 are shown. It will be seen that the end pieces 27' and
28' have a streamlined shape in the form of a dolphin's snout and
have transverse passages forming the ends 29' and 30' and
permitting the fixation of a pedicle screw in an entirely
traditional manner. In this figure, the portion forming the nut 31'
is borne by the lower piece 27'. This nut 31' is traversed by a
threaded rod 40' which is rigidly supported by the upper end piece
28' in such a way that the axial displacement of this rod provokes
the rotation of the piece 28' relative to the piece 27'. The
threaded rod 40', as will be seen in FIG. 61, passes into a pot 41'
which is received in a leaktight manner inside the hydraulic
bellows 32' acting as movable element, and the rod 40' can turn in
this pot about its axis while being retained inside the pot by a
securing ring 42'. It will be seen from this that it is also
possible to give the overall implant an elongate streamlined shape
particularly appropriate for good cohabitation with the surrounding
tissue.
[0423] Referring to FIG. 62, this shows an embodiment of an implant
33' according to FIG. 59 with an upper end 28' and a lower end
piece 34' which has arms 43' ending in a bearing 44' inside which
there can freely turn, while being retained axially by a securing
ring 45', a threaded rod 46' which is integral with the piece 28'
and is capable of turning inside a nut 47' of a pot 48' fixed in a
leaktight manner on the metal bellows 49' at the end integral with
the end piece 34'. It will be appreciated that any movement of the
bellows provokes an axial movement of the nut 47', which provokes a
rotation without axial movement of the piece 28' relative to the
piece 34'.
[0424] We now describe the use of a double implant for the
correction of scoliosis in a patient having an angle of scoliosis
a1 between the two scoliotic vertebral stages. During the
operation, the surgeon employs traditional means to establish a
preliminary correction bringing the angle of scoliosis to the value
a2<a1. He then places the two individual implants on either side
of the vertebral column between the two vertebral stages in
question, with the valve 13' open, which permits the shortening of
one of the individual implants and the compensating elongation of
the other individual implant, and he fixes the two elements with
the aid of their pedicle screws. It then suffices to re-close the
valve 13' so that the two individual implants are blocked in their
position without any possibility of movement and they maintain the
scoliotic part of the vertebral column in the angle a2. From this
moment onwards, all the loads are borne by the prosthesis
constituted by the double implant.
[0425] After a reasonable postoperative period during which the
stresses are supported essentially by the prosthesis, the neutral
point of the vertebral column will adapt by virtue of the
reorganization of the skeletal and paravertebral tissues, and this
will reduce the load on the prosthesis in the standing position. It
is possible either to estimate this reduction in load or to provide
the prosthesis with pressure sensors which can be interrogated,
preferably noninvasively, as is already well known, and which will
indicate that the vertebral column has reached a state of
equilibrium.
[0426] A new adjustment will then be made by asking the patient to
bend sideways to reduce the value of the angle a of scoliosis to a
value a2<a1 after opening the valve 13', which renders the two
implants movable. Once this angle a2 has been obtained, the valve
is closed again so that the two implants maintain this new position
and prevent the return to a greater angle of scoliosis. This
blocking of the prosthesis causes the patient the sensation of an
obstacle which will gradually disappear until such time as a new
equilibrium is found.
[0427] By means of a succession of these maneuvers, it is thus
possible to reduce or even eliminate the angle of scoliosis and to
remove the prosthesis.
[0428] It will be appreciated that the same principles can be used
for gradually re-establishing kyphosis or lordosis by using pairs
of implants which are arranged, for example, in accordance with the
figures.
[0429] Likewise, by using a pair of prostheses as in FIG. 9, for
example, it would be possible to gradually reduce
kyphoscoliosis.
[0430] FIG. 63 shows a transverse cross section of an implant in a
refined embodiment of the invention.
[0431] This implant 1' includes two parts in the form of end pieces
51' and 52`in the shape of a dolphin`s head, having at their
outermost parts holes or eyelets 53' and 54' through which it is
possible to engage pedicle screws whose heads can be fixed rigidly
in the area of the holes 53', 54'. Alternatively, these holes can
be arranged in such a way as to permit an articulation of the head
of the pedicle screw and thus an angular displacement between the
end element and the screw which it bears.
[0432] Arranged between the two end pieces 51' and 52' there is a
third piece 55' which is movable relative to the two ends. The
piece 55' has a stirrup shape, of which one of the branches 56'
supports a metal bellows 57' in a leaktight manner, the free end of
which bellows is fixed in a leaktight manner against a piece 58'
which is able to slide relative to the stirrup 55' and bears, in
the manner of a journal, by virtue of a securing ring 45', but
axially nonmovable relative to the piece 58', a threaded rod 59'
which passes through a complementary tapped hole of the second
branch 60' of the piece 55'. It will thus be appreciated that when
the deformable element constituted by the bellows 57' deforms, the
thus provoked axial displacement of the rod 59' integral with the
upper end 52' entrains the rotation of this rod 59' in the fixed
nut formed in the branch 60', and consequently a simultaneous
movement of translation and rotation of the end piece 52' relative
to the piece 60'.
[0433] Arranged inside the end piece 51' is a leaktight cavity 61'
which serves as a high-pressure chamber and in which there is a
bellows 62' which is hermetically sealed and in which a vacuum has
been established. The stiffness of this bellows, however, is
sufficient to ensure that it tends spontaneously to deploy and
increase in volume even when it is surrounded by high pressure
prevailing in the chamber 61'. The chamber 61' communicates via a
nondeformable conduit 63' with the inside of the metal bellows 57'
by way of a high-pressure valve 64' lodged in the branch 56'. This
valve 64' has a tubular slide of soft iron 65' which is normally
held back by a spring in the position closing off the passage
towards the bellows 57'. It will be appreciated that when the
plunger core 65' is brought into a position of opening counter to
the valve spring, liquid at high pressure in the chamber 61' will
run along the conduit 63' and enter the bellows 57'. The high
pressure in the chamber 61' is maintained by the concomitant
deformation of the sealed bellows 62'. This inflow of liquid
provokes the displacement of the piece 58' towards the branch 60'
and, consequently, the distraction and rotation of the end piece
52' relative to the central piece 55'.
[0434] The inside of the bellows 57' also communicates, by way of a
low-pressure valve 66' equipped with a plunger core identical to
the core 65' situated in the piece 58', with the volume 67'
surrounding the various pieces contained inside the deformable
impermeable sleeve 68', at the two ends of which the ends of the
pieces 51' and 52' emerge, this volume 67' forming the low-pressure
volume. It will be appreciated that when the valve 66' is opened,
liquid contained in the bellows 57' will exit and spread through
the low-pressure volume 67', thus permitting a retraction or
compression of the bellows 57' and a simultaneous rotation of the
piece 52' in the opposite direction.
[0435] The high-pressure reservoir 61' is recharged by way of a
metal bellows 69' which is of a diameter substantially smaller than
that of the bellows 57' and which is interposed between the pieces
51' and 55'. When the pieces 51' and 55' move away from each other,
this bellows 69' expands and aspires liquid from the low-pressure
chamber 67' by way of a nonreturn valve 70'. By contrast, when the
pieces 51' and 56' close together, the high pressure generated in
the bellows 69' causes liquid at very high pressure to enter the
high-pressure chamber 61' by way of a nonreturn valve 71'.
[0436] It is not necessary for the deformation of the bellows 69'
to be of a great amplitude; on the contrary, it is preferable for
the gap between the piece 51' and the piece 56' to be small and for
the course of oscillation between the pieces 51' and 55' to be
limited, a multiplicity of oscillations, for example, as the
subject walks or changes position of his/her body sufficing to
generate the high pressure permitting supply to the chamber
61'.
[0437] In such an embodiment, as long as neither of the valves 64'
and 66' is open, the two pieces 51' and 52' can move relative to
one another only by a very short distance, and this thus ensures
that the two skeletal elements to which they are anchored, for
example two vertebrae, are maintained in the chosen position. The
device for establishing high pressure can even be used to obtain a
certain viscous damping of the small displacements permitted
between the pieces 51' and 55'.
[0438] It will also be appreciated that having arranged the
high-pressure and low-pressure valves 64', 66' on either side of
the bellows 67', one or other of these valves can easily be
actuated, according to choice, for example by a strong magnet
placed on the skin in line with one of the valves in order to
attract the ferromagnetic plunger such as 65' towards the left of
the drawing and to open the valve.
[0439] It will of course be appreciated that it would be possible
to form an implant analogous to that which has just been described,
but arranged so as not to provoke rotation between the two end
pieces, but simply a movement of distraction or compression. It
would also be possible to form an implant such as that in FIG. 13
using most of the structural arrangements in FIG. 14 so as to form
an implant uniquely with rotation.
[0440] By combining with an implant of this type a joining rod
analogous to the rods 7', and by forming at the ends of the pieces
51' and 52' articulation bearings permitting a pivoting of the
pedicle screws relative to the said ends, it is also possible to
form implants according to FIGS. 50, 51, or 54, or 55.
[0441] In the case where use is made of a large number of implants
according to the invention arranged along the vertebral column
between different levels of the spine, it is also possible to
provide a single high-pressure reservoir and a single low-pressure
reservoir as well as a single deformable element for establishing
high pressure, this reservoir assembly being arranged away from the
various individual implants and being connected to each of these by
a low-pressure conduit and a high-pressure conduit, the implants
themselves in this case not having any hydraulic deformable element
other than the motor bellows acting as bellows 57'.
[0442] Also, the controllable valves, such as the valves 13', 19'
or 64' or 66', instead of being controlled directly by way of a
ferromagnetic plunger capable of being attracted by a magnet placed
on the surface of the skin near the valve, could be controlled, in
a hydraulic manner known per se, by a small pilot valve which is
easier to actuate because it has a plunger of lower inertia, the
pilot valve addressing a control pressure to the actual switching
valve in order to open the latter, and the closure of the pilot
valve, by contrast, provoking the closure of the main valve.
[0443] It will also be appreciated that it is possible to limit the
movement of one of the ends relative to the other by providing
traditional abutment means between the two pieces, which come into
force if the travel of the deformable member or of the motor
bellows exceeds a desired amplitude. Thus, this provides an element
of safety in the case of a fault in the functioning of the implant
which prevents it from exactly maintaining the desired position,
for example escape of liquid or conduit deformation or excessive
deformation of a bellows.
[0444] The implants according to the invention are preferably
delivered with a temporary removable element which holds them in a
position of desired spacing between the two end elements and which
the surgeon removes once he has fitted the implant and fixed the
pedicle screws or other anchoring means at the ends of the
implant.
[0445] The invention also relates to a therapeutic surgical
procedure for modifying the position of two portions or elements of
the skeleton, for example two vertebrae, in which procedure at
least one implant element according to the invention is fitted, one
of the ends is fixed by an anchoring means to one of the portions
or elements of the skeleton, and the other end is fixed by an
anchoring means to the other portion or element of the skeleton, if
appropriate after having carried out a preliminary correction of
the relative position of the two portions or elements, the approach
route and the tissues operated on are left to heal, then,
preferably by noninvasive control means, a corrective displacement
or force is produced causing corresponding stressing of the two end
pieces of the implant, or the anchoring means, relative to one
another.
[0446] This displacement can be provoked directly by the patient's
body and, in this case, the displacement is permitted by permitting
deformation of the movable element, for example a hydraulic
bellows, then, when the displacement has been completed, all
subsequent displacements are prohibited by blocking the deformable
element.
[0447] In another embodiment, in order to provoke the displacement,
a deformation of the movable element is temporarily provoked by
applying a force with which it is possible to obtain the desired
displacement, after which the movement of the deformable element is
once again blocked and prevented.
[0448] In a third embodiment, by contrast, the movable element is
allowed to exert a permanent force, preferably constant or possibly
progressively variable, between the two ends and thus the two
portions or elements of the skeleton, with an intensity of force
which is insufficient to provoke an abrupt modification of
dimension and an attack on the tissue opposing this dimensional
variation, but which is sufficient to provoke, as is known per se
in the field of surgery, a slow deformation and an adaptation of
the various tissues until the desired corrected position is
reached.
[0449] Such a procedure is particularly suitable for correction of
scoliosis or kyphoscoliosis.
[0450] When a force is exerted between two skeletal elements by
means of an implant according to the invention, this force can
advantageously be from a few daN to 25 or 30 daN.
[0451] The device can advantageously include force or pressure
sensors for limiting or regulating the force to be exerted. Such
miniaturized sensors are available on the market.
[0452] It has been seen that the noninvasive control means can be
magnets which, from outside the body, can displace or attract a
ferromagnetic mass, such as a valve slide, counter to a spring or
an elastic return means which brings the mass back to its initial
position once the magnet has been removed.
[0453] It is also possible to use an external device which creates
a magnetic or electromagnetic rotary field which, inside the body,
turns a rotary piece, for example a rotary slide of a valve.
* * * * *