U.S. patent number RE36,221 [Application Number 08/648,397] was granted by the patent office on 1999-06-01 for flexible inter-vertebral stabilizer as well as process and apparatus for determining or verifying its tension before installation on the spinal column.
Invention is credited to Francis Henri Breard, Henry J. M. Graf.
United States Patent |
RE36,221 |
Breard , et al. |
June 1, 1999 |
Flexible inter-vertebral stabilizer as well as process and
apparatus for determining or verifying its tension before
installation on the spinal column
Abstract
The present invention relates to an inter-vertebral stabilizer
having one or more flexible ligaments. Each flexible ligament can
be engaged with two respective vertebrae and/or associated with two
retaining elements, such as screws, each of which is suitable for
being implanted in a respective vertebra. The present invention
also relates to a process, and the associated apparatus, for
determining or verifying the tension of such an inter-vertebral
stabilizer before it is put into place on the spinal column. This
process includes implanting, in each of the vertebrae concerned, a
corresponding rigid rod extending outside the patient's body. The
rods in each pair of adjacent rods are immobilized in an initial
position. If the pain which is to be removed by the stabilizer
persists, the process includes modifying the distance between the
rods, then in immobilizing the rods in their new relative positions
and in repeating the pain test. This cycle of operations is
repeated, if necessary, until the pain disappears. The length to be
allocated to the ligament is deduced from the distance then
attained between the two rods.
Inventors: |
Breard; Francis Henri (75014
Paris, FR), Graf; Henry J. M. (69002 Lyons,
FR) |
Family
ID: |
27251804 |
Appl.
No.: |
08/648,397 |
Filed: |
May 15, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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203000 |
Feb 28, 1994 |
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Reissue of: |
474468 |
Feb 2, 1990 |
05092866 |
Mar 3, 1992 |
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Foreign Application Priority Data
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Feb 3, 1989 [FR] |
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89 01445 |
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Current U.S.
Class: |
606/54; 606/251;
606/263; 606/279; 606/302 |
Current CPC
Class: |
A61B
17/7022 (20130101); A61B 2090/061 (20160201); A61B
17/708 (20130101) |
Current International
Class: |
A61B
17/84 (20060101); A61B 17/70 (20060101); A61B
17/68 (20060101); A61B 17/88 (20060101); A61B
017/70 (); A61F 002/44 () |
Field of
Search: |
;606/61,90,60
;623/13,17 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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00159007 |
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Mar 1984 |
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EP |
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0260970 |
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Mar 1988 |
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EP |
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0322334A1 |
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Dec 1988 |
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EP |
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0 348 272 |
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Dec 1989 |
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EP |
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2 309 201 |
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Dec 1976 |
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FR |
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2 596 641 |
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Oct 1987 |
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FR |
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2 623 085 |
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Aug 1994 |
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FR |
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3 625 542 |
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Nov 1987 |
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DE |
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3 807 335 |
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Sep 1989 |
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DE |
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3 095 060 |
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Apr 1988 |
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JP |
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7 610 576 |
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Sep 1976 |
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NL |
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Other References
English translation of Netherlands patent to slot No.
7610576..
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Primary Examiner: Willse; David H.
Attorney, Agent or Firm: Collard & Roe, P.C.
Parent Case Text
.Iadd.This is a continuation of application Ser. No. 08/203,000,
filed on Feb. 28, 1994, now abandoned, which is a reissue of
application Ser. No. 07/474,468, filed on Feb. 2, 1990, now U.S.
Pat. No. 5,092,866. .Iaddend.
Claims
We claim:
1. An inter-vertebral stabilizer comprising at least one flexible
ligament having an all-direction flexibility and at least two
retaining elements, each retaining element having an implant
portion configured to be implanted in a respective one of at least
two successive vertebrae, a free head adjacent the implant portion
for projecting from the respective vertebra when the implant
portion is implanted in said verebra, and a lateral projection
extending laterally from the head at a selected distance from the
implant portion, said ligament being provided, at each end thereof,
with a hanging means having a width less than the distance between
the lateral projection and the implant portion for loose engagement
around the free head of a respective one of the retaining elements,
whereby the loose engagement of the ligament with the respective
retaining element enables compensation for defects of a spine
without hindering flexional and torsional movements thereof.
2. Inter-vertebral stabilizer according to claim 1, in which said
at least one flexible ligament has the general form of a closed
loop, the ends of which constitute said hanging means.
3. An inter-vertebral stabilizer according to claim 2 in which the
lateral projection of each of the retaining elements is provided by
a cap removably fitted on the head of the retaining element, said
cap being radially over-dimensioned in relation to the head of the
retaining element on which the cap is removably fitted, said cap
preventing the ligament from slipping off the free head.
4. The inter-vertebral stabilizer according to claim 2 in which the
lateral projection of each retaining element for retaining the
ligament in loose engagement on the retaining element is unitary
with the head thereof.
5. Inter-vertebral stabilizer according to claim 1, in which said
at least one flexible ligament is provided, at each end thereof,
with a closed loop constituting said hanging means.
6. An inter-vertebral stabilizer according to claim 5 in which the
lateral projection of each of the retaining elements is provided by
a cap removably fitted on the head of the retaining element, said
cap being radially over-dimensioned in relation to the head of the
retaining element on which the cap is removably fitted, said cap
preventing the ligament from slipping off the free head.
7. The inter-vertebral stabilizer according to claim 5 in which the
lateral projection of each retaining element for retaining the
ligament in loose engagement on the retaining element is unitary
with the head thereof.
8. Inter-vertebral stabilizer according to claim 1, in which each
of the retaining elements is provided with a removable cap radially
over-dimensioned in relation to the head of the retaining element
on which the cap can be fitted, the cap comprising the lateral
projection of the retaining element.
9. Inter-vertebral stabilizer according to claim 1 in which the
lateral projection for retaining the ligament in loose engagement
on the retaining element is unitary with the head thereof. .[.10. A
process for stabilizing a length of the spinal column comprising at
least two successive vertebrae, said process comprising the steps
of:
a) providing at least one flexible ligament having an all-direction
flexibility and provided at each end with hanging means for loosely
hanging the flexible ligament,
b) providing at least two retaining elements, each of which has a
free head and an implantation end,
c) making a surgical incision in the patient's body in front of
each vertebra of said length of the spinal column,
d) implanting the implantation end of each retaining element in a
respective one of said successive vertebrae, with said free head
projecting from the vertebra after said retaining element has been
implanted,
e) installing said at least one flexible ligament on two respective
successive retaining elements by passing the hanging means of each
ligament end around the projecting free head of a respective one of
said two successive retaining elements, so that said ligament end
at least partly loosely encircles the free head of said retaining
element thus permitting a movement of the ligament with respect to
the retaining elements during selected flexional movements of the
spinal column, said at least one ligament forming an
inter-vertebral stabilizer together with the
associated retaining elements..]..[.11. The process of claim 10, in
which said inter-vertebral stabilizer comprises a plurality of
ligaments chained along the spinal column by means of the same
plurality, plus one, of retaining elements..]..[.12. The process of
claim 10, further comprising the step of implanting at least one
additional inter-vertebral stabilizer on the back face of said
vertebrae, each of said stabilizers being placed on one respective
side of the spine along the length of the spinal column to be
stabilized..]..[.13. The process of claim 10 comprising additional
steps for determining the length at rest of said at least one
ligament, said additional steps being performed between steps c)
and d) and comprising successively:
implanting a rigid rod in each of the vertebrae concerned and at
the point for implantation of the corresponding retaining element,
with said rod extending out of the patient's body,
immobilizing the two rods of each pair of adjacent rods at a
predetermined distance from one another,
performing a pain test by permitting a selected amount of time to
elapse and determining whether a pain to be removed by the
stabilizer persists, and
in the event where the pain, the cause of which is to be removed by
the stabilizer is persisting after the selected time has elapsed,
modifying the distance between the rods by a selected pitch,
immobilizing the rods in their new relative positions and carrying
out the pain test again, by allowing the time to elapse and
determining whether the pain persists, the steps of modifying the
distance, immobilizing and testing for pain being repeated, if
necessary until the pain disappears, the length at rest to be given
to the ligament then being deduced from the value of the distance
then attained between the two rods..]..[.14. Apparatus for
implement the process according to claim 13, characterized in that
the apparatus comprises a set of at least two rods (11,12) each
having an implantation end (2,3) for implanting in the respective
vertebra (V1, V2), the rods being associated with at least one
rigid link (15) of adjustable length for joining the rods at a
point remote from their implantation ends..]..[.15. Apparatus
according to claim 14, characterized in that the implantation end
of each rod is constituted by the corresponding retaining element
(2,3) of the ligament of the said stabilizer and each of the rods
(11,12) further comprises a removable extension piece (13) fitting
onto the head (4) of said retaining element..]..[.16. Apparatus
according to claim 15, characterized in that the said length
adjustable rigid link (15) comprises a thin bar (16) and two
collars (17,18) that can be fitted respectively on the two rods
(11,12) and are provided with means (20) for supporting the bar
slidingly between them, an element (19) for locking the bar (16)
being provided on each collar..]..[.17. Apparatus according to
claim 14, characterized in that it comprises an instrument (24) for
determining the length at rest of the ligament, which is formed by
two crossed legs (25,26) articulated on one another at their
middle, the ends of the legs located on the same side of the
articulation (27) each having a substantially semi-circular
contacting portion (28,29)..]..[.18. An inter-vertebral stabilizer
comprising at least one flexible ligament having an all-direction
flexibility and at least two retaining elements, each retaining
element having an implantation end implantable in a respective one
of two successive vertebrae and a projecting free head, said
ligament being provided at each end thereof with a hanging means
for loosely engaging around the free head of a respective one of
the retaining elements, at least two rods each having an end for
temporary implantation in the respective vertebra, the rods being
associated with at least one rigid link of adjustable length for
joining the rods at a point remote from their implantation ends,
whereby the rods and the link are employed for determining a proper
relative position for stabilizing the vertebrae, and whereby the
retaining elements and the ligament are employed for stabilizing
the vertebrae in the relative position determined with the rods and
the rigid link of adjustable length..]..[.19. A stabilizer as in
claim 18 wherein the implantation end of each said rod is defined
by a corresponding one of the retaining elements, the rods being
selectively removable from the retaining elements after determining
the preferred relative position for stabilizing the
vertebrae..]..[.20. A stabilizer according to claim 18 wherein the
rigid link of adjustable length comprises a pair of collars
slidably engaged on the respective rods and a bar adjustably
engagable by the collars for locking the rods in selected positions
relative to one another..]..[.21. A stabilizer according to claim
18 further comprising an instrument for determining the length at
rest of the ligament, the instrument comprising a pair of crossed
legs articulated to one another at their middle, the ends of the
legs each having a substantially semi-circular contacting portion
for engaging the rods at locations thereon generally adjacent the
respective
vertebrae..]..Iadd.22. An intervertebral stabilizer comprising:
at least one supple band made of a flexible plastics material
having all-directional flexibility;
at least two retaining elements, each of said at least two
retaining elements for being implanted in a respective one of at
least two adjacent vertebrae;
said at least one supple band including hanging means for loosely
engaging around two of said retaining elements, wherein said two
retaining elements are movable toward each other by said
loosely-engaged supple band; and
said at least one supple band being sized and configured such that
the loose engagement and relative movement between said band and
the retaining elements enable compensation for defects of a spine
without hindering flexional and torsional movements thereof.
.Iaddend..Iadd.23. The intervertebral stabilizer according to claim
22, wherein said supple band has the form of a closed loop with
spaced opposite ends constituting said hanging means.
.Iaddend..Iadd.24. The intervertebral stabilizer according to claim
22, wherein said supple band includes two spaced opposite ends each
provided with a closed loop or ring constituting said hanging
means. .Iaddend..Iadd.25. The intervertebral stabilizer according
to claims 22, 23 or 24, wherein each of said retaining elements has
a free head for engaging said band. .Iaddend..Iadd.26. The
intervertebral stabilizer according to claim 25, wherein said free
head of said retaining element is provided with a lateral
projection, said lateral projection preventing said band from
slipping off said free head. .Iaddend..Iadd.27. The intervertebral
stabilizer according to claim 26, wherein said retaining element is
a screw. .Iaddend..Iadd.28. The intervertebral stabilizer according
to claim 25, wherein said retaining elements additionally comprise
a cap removably fitted on said free head of said retaining element,
said cap being radially over-dimensioned in relation to said free
head of said retaining element on which said cap is removably
fitted, said cap preventing said band from slipping off said free
head. .Iaddend..Iadd.29. The intervertebral stabilizer according to
claim 28, wherein said retaining element is a screw. .Iaddend.
Description
The present invention relates to an inter-vertebral stabilizer to
be installed between at least two vertebrae to correct defects in
the spinal column.
Inter-vertebral stabilizers currently used to attenuate the often
painful effects of diseases of the spinal column, such as
scolioses, nucleus pulposus herniations or lumbar instabilities,
take the form of metal plates or rods that are fixed to the
vertebrae or to their spines, along the affected section of the
spinal column, which has the drawback of completely immobilizing
the vertebrae, hence of restricting or even completely preventing
flexional or torsional movements of the patient's trunk.
The present invention proposes to overcome this drawback and, for
that purpose, it provides an inter-vertebral stabilizer of a novel
type which is characterized in that it comprises one or more
flexible ligaments having an all-direction flexibility, each of
them being provided with means for fastening it to two respective
vertebrae and/or associated with two retaining elements, each of
which can be implanted in a respective vertebra.
Advantageously, the flexible ligament has the general form of a
closed loop or, alternatively, is provided with a ring or a closed
loop at each end thereof, whereby the ends of each ligament
constitute said fastening means through which said ligament can be
fastened by hanging to a spine or any other protrusion of a
respective vertebra. When retaining elements are provided, each of
them, being preferably a screw, is advantageously formed with a
free head for fastening a respective end of the corresponding
ligament.
There is thus obtained a flexible or semi-elastic inter-vertebral
stabilizer which, according to its mode of implantation, on one
side only or on both sides of the spines of the vertebrae
concerned, on the front face or the rear face thereof, with a
single ligament or with several ligaments chained together or even
crossed with each other, makes it possible to compensate for all
sorts of defects or deformations of the spinal column by permitting
sufficient clearance between the vertebrae not to hinder the
patient in the flexional or torsional movements of his trunk.
Apart from this main advantage, the inter-vertebral stabilizer
according to the invention is extremely simple to install: it
suffices to engage the end of each ligament around for example two
vertebral spines or two screws pre-implanted in the vertebrae.
To prevent any slipping of the ligament once it has been put in
place, in the case where retaining elements, such as screws, are
used, provision is also advantageously made for fitting onto each
retaining element, a removable cap that is radially
over-dimensioned in relation to the head of the retaining element.
The same effect can be obtained by alternatively providing the head
of each retaining element with a lateral projection for retaining
the ligament.
Before putting the stabilizer in place on the spinal column, its
tension, i.e. the length at rest of the, or of each, flexible
ligament, will naturally have to be determined precisely in
accordance with the seriousness of the defect to be corrected and,
for this purpose, the present invention proposes a process
comprising the steps which consist successively:
in making a surgical incision in the patient's body in front of
each vertebra concerned for uncovering it,
in implanting a rigid rod in each of the vertebrae concerned and at
the point at which the corresponding ligament is to be fixed, with
said rod extending out of the patient's body,
in immobilizing the two rods of each pair of adjacent rods, at a
predetermined distance from one another, and
in the event where the pain, the cause of which is to be removed by
the stabilizer, is persisting after a given time period has
elapsed, in modifying the distance between the rods by a certain
pitch, and then in immobilizing the latter in their new relative
positions and in carrying out the pain test once again, this cycle
of operations being repeated, if necessary, until the said pain
disappears, the length at rest to be given to the ligament then
being deduced from the value of the distance then attained between
the two rods.
This process can also be implemented for verifying and modifying
the tension of one or more ligaments already in place on the spinal
column, when the patient experiences pain after a less or more long
period of use.
Another object of the invention is to provide an apparatus for
determining the tension of an inter-vertebral stabilizer according
to the invention before it is put into place on the spinal column,
the said apparatus being characterized in that it comprises a set
of at least two rods each having an end for implantation in the
corresponding vertebra, these rods being associated at least with a
rigid link of adjustable length designed to join them together at a
point remote from their implantation ends.
According to a preferred embodiment, the implantation end of each
rod is constituted by an element having a head onto which is
removably fitted an extension piece forming the remaining portion
of the rod, designed to receive the rigid length-adjustable
link.
Once the operation of determining the tension of the
inter-vertebral stabilizer has been completed, the end elements of
the rods, which will preferably be screws, can be advantageously
held in place in the vertebrae to form the ligament retaining
elements, and the ligament, after being produced to the length
calculated using the process according to the invention, can easily
be engaged around the said screws by sliding along the extension
pieces before they are removed.
The rigid length-adjustable link can, for its part, take various
forms, the simplest being that of a thin bar and two collars that
can be fitted respectively onto the two rods and are provided with
means for slidably supporting the bar between them, a bar locking
member being provided on each collar.
Advantageously, the apparatus according to the invention further
comprises an instrument for determining the length at rest of a
ligament, which is formed by two crossed legs articulated on one
another at their middle, the ends of the legs located on the same
side of the articulation each having a substantially semi-circular
contacting portion, which is applied onto the head of the
corresponding retaining element. In this way, it is possible to
determine between the other ends of the two legs of this instrument
the length required for the ligament to be implanted, which can be
measured using a graduated rule.
Embodiments of the inter-vertebral stabilizer according to the
invention, together with a process and an apparatus for determining
their tension, will now be described in greater detail, but non
limitatively, with reference to the accompanying drawings,
wherein:
FIG. 1 shows a side view in partial cross-section of the
inter-vertebral stabilizer according to the first embodiment of the
invention;
FIG. 2 is a front view of an inter-vertebral stabilizer according
to the second embodiment of the invention;
FIGS. 2a and 2b show alternative embodiments of the stabilizer of
FIG. 2;
FIGS. 3a, 3b and 3c illustrate one of the ligament retaining
elements of the stabilizer of FIG. 1;
FIGS. 4a and 4b show, in longitudinal cross-sectional view and in
front view respectively, one of the ligament retaining elements of
the stabilizer of FIG. 2;
FIG. 5 is a side view, in partial cross-section, of the apparatus
according to the invention, represented in use on two adjacent
vertebrae;
FIG. 6 is a cross-sectional view along line VI--VI of FIG. 5;
FIG. 7 illustrates in its position of use, a supplementary
accessory of this apparatus, designed to determined the length at
rest of the ligament; and
FIG. 8 represents the apparatus of FIG. 5 as used for the insertion
of the flexible ligament around the retaining elements.
FIG. 1 represents two adjacent vertebrae, V1, V2, of a patient's
spinal column, linked by an inter-vertebral stabilizer according to
the invention, which is composed of a flexible .Iadd.or supple
.Iaddend.ligament 1 in the form of a closed loop .Iadd.or band
.Iaddend.and of two screws 2,3 each implanted in a corresponding
vertebra to retain ligament 1 between them, said ligament being
simply engaged around the widened cylindrical heads 4 of the
screws, emerging from the vertebrae. Ligament 1 is an artificial
ligament made of "Dacron" (registered trade-mark) or of any other
flexible plastics material, having an all-direction
flexibility.
As more clearly shown in the longitudinal cross-sectional and front
views of FIGS. 3b and 3c, the head 4 of each screw comprises an
axial blind hole 5 having a hexagonal cross-section, in which a
hexagonal key can be engaged in order to implant the screw in the
corresponding vertebra.
After ligament 1 has been put into place around the screws thus
implanted, hole 5 of each of said screws is closed using a flat
circular cap or plug 6, shown alone in FIG. 3a, said cap, the
diameter of which is substantially larger than that of head 4 of
the screw, being screwed by means of a central pin 7 with a
threaded end into a threaded bore 8 opening in the bottom of hole
5. To accomplish this screwing operation, use is made of a special
key cooperating with two slots, 9,9a, formed on the periphery of
each cap 6. Alternatively, each cap may be provided with a central
hexagonal bore and screwed on the head 4 of the corresponding screw
by using a hexagonal key engaged in this bore. By projecting
radially right around the corresponding heads 4 of the screws, the
two caps 6 preclude any likelihood of ligament 1 slipping off the
said heads, as illustrated in FIG. 1.
The caps 6 are particularly useful when the inter-vertebral
stabilizer according to the invention comprises several
supplementary flexible ligaments, such as illustrated at 1a and 1b
in FIG. 1, chained together with first ligament 1, on the vertebrae
preceding and following the two designed by V1,V2, with the help of
the same number of supplementary retaining screws.
In the case illustrated in FIG. 2, in which only one ligament 1 in
the form of a closed loop will have to be interposed between only
two successive vertebrae V1,V2, the head 4 of each screw 2 or 3 can
be provided alternatively with a lateral projection 10 of suitable
height, as represented in profile and in front view in FIGS. 4a and
4b. In this case, it will be necessary first of all to implant the
two screws 2,3 by orientating their projections 10 opposite one
another so that ligament 1 can be then slid without any impediment
around their heads 4, after which the screws will be given an
additional half-turn to place projections 10 in their ligament
retaining positions, as shown in FIG. 2.
The inter-vertebral stabilizer according to the invention makes it
possible, according to its positioning, to combat numerous painful
diseases affecting the spinal column. The stabilizer shown in FIGS.
1 and 2 is put into place on the rear face of vertebrae V1,V2 and
on one side only of their spines A1,A2. However, depending on the
type of disease to be treated, it is possible to use two
stabilizers according to the invention, mounted on either side of
vertebral spines A1,A2 or crossed between the two vertebrae V1,V2,
on the front or rear face thereof. In all cases, however, it is
necessary to determine the tension of the stabilizer, i.e. the
length at rest of its ligament 1, accurately before it is
installed, as a function of the seriousness of the defect to be
corrected. For this purpose, the present invention proposes a
process and an apparatus for its implementation, which will now be
described with reference to FIGS. 5 to 8.
As it can be seen, the basic accessories of this apparatus are two
rigid rectilinear rods, 11,12, which are fixed in the respective
vertebrae V1,V2 by their ends which, in the preferred embodiment
represented in FIG. 5, are formed by screws 2,3 of what is to
become the stabilizer. Each screw is implanted in the way described
above after a local surgical incision has been made in the
patient's back in front of each vertebra for uncovering it. Each
rod 11,12 is completed by a cylindrical extension piece 13 having a
threaded end 14, which is fitted onto the head 4 of the
corresponding screw by screwing into its threaded bore 8 after
removal of cap 6. For this purpose, the free opposite end of each
extension piece 13 is provided with a hexagonal head 23 suitable
for receiving a tightening key. It will also be noted that each
extension piece 13 has a foot 13a which flares progressively until
its diameter is substantially equal to that of the head of screw 4
onto which it is fitted.
The two rods 11,12 being thus implanted so as to extend out from
the patient's back D, they are joined in the vicinity of their free
ends 23 by a rigid link 15 of adjustable length and, by means of
the latter, the distance between the rods is adjusted to a value
that is predetermined as a function of the nature and the
seriousness, previously diagnosed, of the defect to be corrected on
the spinal column.
After the two rods have been thus immobilized in this initial
position, the incisions in the patient's back are closed up and the
patient is made to undergo a test which consists in verifying
whether, at the end of a given period, possibly one to two days,
the patient still experiences pain in the affected area of the
spinal column. If this is the case, the spacing between rods 11,12
is slightly modified, generally for bringing them closer to one
another (compression), by acting on the length of link 15, and the
pain test is repeated over substantially the same period of time as
before.
This dual operation will be repeated if necessary, preferably with
a constant pitch of change in the spacing of rods 11, 12, until the
patient no longer experiences any pain in the back. Once this
result has been achieved, the length at test required for the
ligament to be implanted between the vertebrae is measured or
calculated with maximum accuracy.
In practice, the maximum number of successive cycles of verifying
operations leading to the elimination of pain will be three and, if
the pain proves to persist after these three cycles of operations,
this will mean that the defect that causes it is not present in the
pair of vertebrae tested and the process according to the invention
will then have to be applied to the following pair of vertebrae or
successively on the following pair(s) of vertebrae, until the pain
disappears.
Of course, when several flexible ligaments are to be chained
together, such as 1, 1a and 1b (FIG. 1), over a long section of the
spinal column, the above described process will be applied
simultaneously to all the successive vertebrae to be treated, using
as many rods 11,12 as there are vertebrae and joining them two by
two using length adjustable links such as 15.
This link, which is more clearly represented in FIG. 6, is in fact
formed here by a thin cylindrical bar 16 retained on two collars
17,18 each of which is fixed to a corresponding rod 11, 12 by means
of a lock screw 19. Bar 16 is more precisely housed so as to be
able to slide freely in a groove 20 of each of collars 17,18 and is
locked therein, after the spacing of the rods has been adjusted, by
head 21 of lock screw 19 of the corresponding collar.
Alternatively, of course, link 15 can take the form of a device
with threaded rods with reversed screws pitches, which could even
be fitted with a system for directly measuring the spacing between
rods 11,12.
The length to be allocated to the ligament can be derived, by a
trigonometrical calculation, from the distance d measured, for
example near link 15, between rods 11,12 immobilized in the right
position. According to an additional feature of the invention,
however, it is possible, as an alternative, to measure directly the
length to be allocated to ligament 1 between heads 4 of screws 2,3
by using an instrument which will now be described, together with
its mode of use, with reference to FIG. 7.
As it can be seen, this instrument 24 for determining the length of
the ligament takes the general form of a "pair of scissors" and is
more specifically, formed by two legs, 25,26, of the same length,
which cross in their middle and are articulated on one another at
their point of crossing by means of a lock screw 30. On the same
side of this articulation 30, the ends of the two legs 25,26 carry
a contacting piece, 28 or 29, which is substantially semi-circular
and has a inner diameter slightly greater than that of the heads 4
of retaining screws 2,3. These contacting pieces 28 and 29 are
facing each other and their inner arcuate face is flush with the
inner side of the corresponding leg 25 or 26 of instrument 24. At
their opposite ends, legs 25,26 are each provided with a ring,
31,32, to accommodate a finger.
To measure the length of the ligament using the said instrument 24,
an incision is first made in the patient's back as far as vertebrae
V1, V2 are uncovered. Then, after having loosened screw 30 and by
holding instrument 24 in one hand by means of rings 31,32, each of
contacting pieces 28 or 29 is placed on a respective rod 11 or 12
and the instrument is caused to slide along these rods until the
contacting pieces are bearing on the ends of heads 4 of screws 2,3.
Screw 30 is then re-tightened and, using a graduated rule 33, the
distance between the free ends, 25a, 26a of legs 25,26 of
instrument 24 is measured and the value of the length required for
the ligament to be implanted between retaining screws 2,3 is thus
obtained directly.
After this length measurement, ligament 1 or each of ligaments 1,
1a, 1b to be implanted is prepared from a tubular artificial
ligament which is flattened and sewn back on itself. After link 15
has been removed, the ligament thus formed into a loop is passed
around the two extension pieces 13 and slid along them up to screws
2,3, around the heads 4 of which it is then engaged with the help,
if necessary, of a special semi-cylindrically shaped tool 22, as
shown in FIG. 8. Extension pieces 13 are then removed, caps 6 are
screwed onto the heads of screws 2,3 (FIG. 1) or the latter are
orientated in such a way as to place their projections 10 in
ligament retaining position (FIG. 2); then the incisions in the
patient's back is definitively closed up.
It goes without saying that numerous modifications can be made in
the inter-vertebral stabilizer and in the apparatus that have just
been described.
For instance, according to an alternative embodiment, shown on FIG.
2a, of the stabilizer of FIG. 2, the ligament 1c is in the form of
a single segment 40 to each end of which a metallic ring 41 or 42
is attached, with which the ligament can be fastened by hanging
over the head 4 of a respective retaining screw 2 or 3.
According to another alternative embodiment shown on FIG. 2b, the
ligament 1d of the stabilizer, having the form of a closed loop, is
passed through itself for defining a first end loop 43 which is
engaged around the spine A.sub.1 of a respective vertebra V.sub.1.
At its second end, the ligament 1d is placed around spine A2 of the
lower vertebra V.sub.2, then re-passed through itself for forming a
second end loop 45 after insertion of a locking pin 44. Spines
A.sub.1 and A.sub.2 here play the role of the retaining screws 2,3,
but it goes without saying that ligament 1d of FIG. 2b can also be
associated with such screws, as those 1 and 1c of FIGS. 2 and 2a.
Inversely, ligaments 1 and 1c of FIGS. 2 and 2a can be fastened by
an hanging connection directly over spines A.sub.1 and A.sub.2 of
vertebrae V.sub.1 and V.sub.2, without the use of retaining screws,
as the ligament 1d of FIG. 2d. Of course, a chained arrangement of
a plurality of ligaments, as the one shown on FIG. 1, may also be
obtained with the embodiments of FIGS. 2a and 2b, by means of
pre-implanted retaining screws or by direct fastening over the
spines of the vertebrae concerned.
For their part, screws 2,3 could be replaced by any other retaining
element capable of being implanted in a vertebra and provided with
a free head for fastening a ligament end thereover.
Furthermore, rods 11, 12 of the apparatus of the present invention
can be made in a single piece, the two-piece form of embodiment
described above being preferable, however, when ligament retaining
elements, such as screws, are used because, in this case, it
precludes the need to reimplant said retaining elements after the
preliminary operation for determining the tension of the
stabilizer.
It should further be pointed out that the screws or other retaining
elements 2,3 their caps 6 and rods 11,12 will preferably be made
from a bio-compatible metallic alloy.
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