U.S. patent application number 14/010964 was filed with the patent office on 2014-03-06 for dynamic anchoring device and dynamic stabilization device for bones, in particular for vertebrae, with such an anchoring device.
This patent application is currently assigned to Biedermann Technologies GmbH & Co. KG. The applicant listed for this patent is Biedermann Technologies GmbH & Co. KG. Invention is credited to Lutz Biedermann, Jurgen Harms, Helmar Rapp.
Application Number | 20140066986 14/010964 |
Document ID | / |
Family ID | 33394262 |
Filed Date | 2014-03-06 |
United States Patent
Application |
20140066986 |
Kind Code |
A1 |
Biedermann; Lutz ; et
al. |
March 6, 2014 |
DYNAMIC ANCHORING DEVICE AND DYNAMIC STABILIZATION DEVICE FOR
BONES, IN PARTICULAR FOR VERTEBRAE, WITH SUCH AN ANCHORING
DEVICE
Abstract
A dynamic anchoring device is described. An element with a shank
for anchoring in a bone or a vertebra and with a head connected to
the shank is provided with a receiving part for the head and with
an elastomeric pressure element acting on the head. The pressure
element is formed and located in such a way that, upon a movement
of the element from a first angular position of the shank relative
to the receiving part into a second angular position, it exerts a
return force on the head. Further, a dynamic stabilization device,
in particular for vertebrae, is provided. In such a stabilization
device, a rod is connected two anchoring devices. At least one of
the anchoring devices is constructed as dynamic anchoring
element.
Inventors: |
Biedermann; Lutz;
(VS-Villingen, DE) ; Harms; Jurgen; (Karlsruhe,
DE) ; Rapp; Helmar; (Deisslingen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Biedermann Technologies GmbH & Co. KG |
Donaueschingen |
|
DE |
|
|
Assignee: |
Biedermann Technologies GmbH &
Co. KG
Donaueschingen
DE
|
Family ID: |
33394262 |
Appl. No.: |
14/010964 |
Filed: |
August 27, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10841862 |
May 6, 2004 |
8562652 |
|
|
14010964 |
|
|
|
|
60469086 |
May 7, 2003 |
|
|
|
Current U.S.
Class: |
606/257 ;
606/278; 606/305 |
Current CPC
Class: |
A61B 17/7038 20130101;
A61B 17/7008 20130101; A61B 17/746 20130101; A61B 17/8605 20130101;
A61B 17/7035 20130101; A61B 17/7032 20130101 |
Class at
Publication: |
606/257 ;
606/278; 606/305 |
International
Class: |
A61B 17/70 20060101
A61B017/70; A61B 17/86 20060101 A61B017/86 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 2003 |
DE |
103 20 417.2 |
Feb 27, 2004 |
EP |
PCT/EP2004/001978 |
Claims
1. A dynamic anchoring device comprising an element having a shank
for anchoring in a bone or a vertebra and a head connected to the
shank, a receiving part for receiving the head, and a pressure
element acting on the head, wherein the pressure element is formed
so as to be resilient in such a way that upon a movement of the
element from a first angular position of the shank relative to said
receiving part into a second angular position the pressure element
exerts a return force onto the head to urge the element towards the
first angular position.
2. The dynamic anchoring device according to claim 1, wherein the
pressure element acts on a side of the head facing away from the
shank.
3. The dynamic anchoring device according to claim 1, wherein the
pressure element is formed of an elastomer.
4. The dynamic anchoring device according to claim 1, wherein the
pressure element comprises at least one spring element.
5. The dynamic anchoring device according to claim 1, wherein the
head comprises a flat surface on a side facing away from the shank
and the pressure element comprises a flat surface cooperating
therewith.
6. The dynamic anchoring device according to claim 5, wherein the
head comprises a collar on the side facing away from the shank.
7. The dynamic anchoring device according to claim 1, wherein the
receiving part comprises a support surface to support the head, the
support surface and/or the head being polished or coated to reduce
friction.
8. The dynamic anchoring device according to claim 1, further
comprising a rigid element acting on the pressure element on a side
of the pressure element opposite to the head.
9. The dynamic anchoring device according to claim 1, wherein the
head and the shank are separate parts.
10. The dynamic anchoring device according to claim 9, wherein the
head has a central axis and the shank is connectable to the head at
a predetermined angle .alpha. to the central axis.
11. The dynamic anchoring element according to claim 1, wherein the
pressure element is substantially cylindrical and comprises a first
section which is resilient and a second section which is rigid and
which is located on a side opposite to the head.
12. The dynamic anchoring device according to claim 11, wherein the
second section comprises a U-shaped recess to receive a rod to be
received in the receiving part, the recess forming two free legs
and wherein a depth of the recess is greater than the diameter of
the rod.
13. The dynamic anchoring device according to claim 11, wherein the
first section and the second section are separate parts.
14. The dynamic anchoring device according to claim 1, wherein the
pressure element is formed by an insert made of an elastomer and
having a support surface for the head to rest against.
15. The dynamic anchoring device according to claim 1, wherein a
second elastic pressure element is provided encompassing the head
in a ring shape.
16. The dynamic anchoring device according to claim 15, wherein the
second pressure element is shaped as O-ring or as a molded
ring.
17. The dynamic anchoring device according to claim 1, wherein the
receiving part comprises a U-shaped recess for inserting a rod and
the pressure element is arranged between the head and the rod when
the rod is inserted into the receiving part.
18. The dynamic anchoring device according to claim 17, wherein the
pressure element is pre-compressed by the rod when the rod lies on
the bottom of the U-shaped recess.
19. The dynamic anchoring device according to claim 1, wherein the
pressure element is arranged in the receiving part under bias.
20. A dynamic stabilization device for bones, in particular for
vertebrae, having at least two anchoring devices connected to a
rod, wherein at least one of the anchoring devices comprises an
element having a shank for anchoring in a bone or a vertebra and a
head connected to the shank, a receiving part for receiving the
head, and a pressure element acting on the head, wherein the
pressure element is formed so as to be resilient in such a way that
upon a movement of the element from a first angular position of the
shank relative to said receiving part into a second angular
position the pressure element exerts a return force onto the head
to urge the element towards the first angular position.
21. The dynamic stabilization device according to claim 20, wherein
a spring element is provided on the rod.
22. The dynamic stabilization device according to claim 21, wherein
the spring element is arranged between the anchoring devices.
23-26. (canceled)
27. A dynamic anchoring device comprising: an element having a
shank for anchoring in a bone or a vertebra and a head connected to
the shank, a receiving part for receiving the head, the receiving
part being connected to an external device, a pressure element
acting on the head, wherein the pressure element is formed so as to
be resilient in such a way that when the bone or the vertebra moves
a force acting on the external device is prevented from being
transmitted to the shank.
28. A dynamic anchoring device comprising an element having a shank
for anchoring in a bone or a vertebra and a head connected to the
shank, a receiving part for receiving the head, the receiving part
having a longitudinal axis and a bore hole through which the shank
is inserted, and a resilient pressure element located along the
longitudinal axis and acting on the head.
29. A dynamic stabilization device for bones, in particular for
vertebrae, having at least two anchoring devices connected to a
rod, wherein at least one of the anchoring devices comprises: an
element having a shank for anchoring in a bone or a vertebra and a
head connected to the shank, a receiving part for receiving the
head, and a resilient pressure element acting on the head, wherein
the pressure element is located between the rod and the head when
the devices are connected to the rod.
30-31. (canceled)
Description
FIELD OF THE INVENTION
[0001] The invention relates to a dynamic anchoring device and a
dynamic stabilization device for bones, in particular for
vertebrae, with such an anchoring device.
BACKGROUND OF THE INVENTION
[0002] Intervertebral disc defects can be treated by removal of the
defective intervertebral disc by surgery and osseous fusion of the
intervertebral space with the two adjacent vertebral bodies. In
this method the sections of the vertebral column adjacent to the
fused vertebral column segment can be overstressed, especially in
the area of the intervertebral disc. Another method for treatment
is to remove the defective intervertebral disc and, thereafter, to
insert an artificial intervertebral disc. In the majority of cases,
the rear facet joints and the ligamentous apparatus also are
damaged severely. Thus, there is usually no longer any natural
control of movement of the artificial intervertebral disc from the
posterior side. Consequently, high shearing and rotational forces
have an abrasive effect on the vertebral column segment being
treated.
[0003] DE 42 39 715 C2 describes a fixation system for stabilizing
vertebrae, in which rotational and alternating pressure and tension
loads on the part fixed in the bone can be reduced. However,
elastic damping or control of the occurring movements is not
possible.
[0004] EP 0 669 109 B1 describes a device for stabilizing adjacent
thoracic vertebrae allowing a damaged intervertebral disc and the
intervertebral joints to be partially released from stress from the
posterior side. The device comprises two pedicle screws which are
rigidly connected, respectively, to a strap consisting of an
elastic synthetic material and which are connected to one another
via the biased strap. A pressure-resistant body slipped onto the
elastic strap is further provided between the two screw heads to
transmit pressure forces. The use of a textile strap of this kind
with a pressure-resistant body, however, does not enable any
multi-axial guidance stability of the motion segment of a vertebral
column.
[0005] U.S. Pat. No. 5,474,555 describes a polyaxial bone screw
with a screw element and a receiving part connected thereto for
receiving a rod which allows limited motion between the receiving
part and the vertebra. However, elastic damping of the motion is
not possible with this screw.
[0006] U.S. Pat. No. 5,961,356 describes an anchoring element in
form of a polyaxial bone screw which has a pressure element acting
upon the head, wherein the pressure element comprises a spring
element acting upon the inserted rod.
[0007] U.S. Pat. No. 5,562,737 discloses an extra-discal
intervertebral prosthesis comprising at least a partially closed,
elongated body including a compression chamber having an elastic
block at one end. The block has a free face abutted by a ball joint
associated with a first of two fixation means engageable in spaced
vertebrae of a patient.
[0008] Thus, new anchoring devices continue to be sought which
allow dynamic anchoring of a mechanical device, such as, e.g. a
rod, in a bone or a vertebra and which can be used in particular
for a dynamic stabilization device for stabilizing motion control
and relieving the stress on an artificial intervertebral disc. In
addition, it is desirable to have a dynamic stabilization device
for bones, in particular for vertebrae, which allows motion control
and stress relief on the human intervertebral disc from the
posterior side.
SUMMARY OF THE INVENTION
[0009] The present invention provides an anchoring device
comprising an element having a shank for anchoring in a bone or a
vertebra and a head connected to the shank, a receiving part for
receiving the head, and a pressure element acting on the head,
wherein the pressure element is resilient so that upon a movement
of the element from a first angular position of the shank relative
to said receiving part into a second angular position the pressure
element exerts a return force onto the head to urge the element
towards the first angular position.
[0010] Preferred embodiments of a bone anchoring element in
accordance with the invention have one or more of the following
features:
[0011] the pressure element acts on the side of the head facing
away from the shank;
[0012] the pressure element is formed of an elastomer;
[0013] the pressure element comprises at least one spring
element;
[0014] the head comprises a flat surface on the side facing away
from the shank and the pressure element comprises a flat surface
cooperating therewith;
[0015] the head comprises a spherical segment-shaped section
adjacent to the shank and a collar on the side facing away from the
shank;
[0016] the receiving part comprises a support surface to support
the head, the support surface and/or the head being polished or
coated to reduce friction;
[0017] a rigid element acting on the pressure element on a side of
the pressure element opposite to the head is provided;
[0018] the head and the shank are separate parts;
[0019] the head has a central axis and the shank is connectable to
the head at a predetermined angle .alpha. to the central axis;
[0020] the pressure element is substantially cylindrical and
comprises a first section which is resilient and a second section
which is rigid and which is located on a side opposite to the
head;
[0021] the second section comprises a U-shaped recess to receive a
rod to be received in the receiving part, the recess forming two
free legs and wherein a depth of the recess is greater than the
diameter of the rod;
[0022] the first section and the second section are separate
parts;
[0023] the pressure element is formed by an insert made of an
elastomer and having a support surface for the head to rest
against;
[0024] a second elastic pressure element is provided encompassing
the head in a ring shape;
[0025] the second pressure element is shaped as O-ring or as a
molded ring;
[0026] the receiving part comprises a U-shaped recess for inserting
a rod and the pressure element is arranged between the head and the
rod when the rod is inserted into the receiving part; the pressure
element is pre-compressed by the rod when the rod lies on the
bottom of the U-shaped recess; and/or
[0027] the pressure element is arranged in the receiving part under
pre-stress.
[0028] The invention also provides a dynamic stabilization device
for bones, in particular for vertebrae, having at least two
anchoring devices connected to a rod, wherein one of the anchoring
devices is formed as the anchoring device described above.
[0029] Additionally, the invention provides a method for using the
dynamic anchoring device and a method for stabilizing bones, in
particular for stabilizing vertebrae, wherein the anchoring device
is formed as the anchoring device described above.
[0030] Further features of the invention emerge from the
description of embodiments using the figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 shows an illustration in partial section of a first
embodiment of the anchoring device in the unloaded state.
[0032] FIG. 2 shows an illustration in partial section of the
anchoring device according to FIG. 1 in the loaded state in the
resting position.
[0033] FIG. 3 shows an illustration in partial section of the
anchoring device of FIG. 1 in the loaded state during the action of
a force upon the anchoring element.
[0034] FIG. 4 shows a schematic illustration of a second embodiment
of the pressure element of the embodiment of the anchoring element
shown in FIGS. 1 to 3.
[0035] FIG. 5a shows an illustration in partial section of a second
embodiment of the anchoring element.
[0036] FIGS. 5b-5e show manufacturing steps for manufacturing the
screw element of a modification of the second embodiment.
[0037] FIG. 6 shows a sectional illustration of a third embodiment
of the anchoring element.
[0038] FIG. 7 shows a schematic illustration of the first
embodiment of the dynamic stabilization device.
[0039] FIG. 8 shows a schematic illustration of a second embodiment
of the dynamic stabilization device in a first example of
application.
[0040] FIG. 9 shows a schematic illustration of the second
embodiment of the dynamic stabilization device in a second example
of application.
[0041] FIGS. 10a-10c show a sectional illustration of a further
embodiment of the dynamic anchoring device.
[0042] FIG. 11 shows a sectional illustration of a further
embodiment of the dynamic anchoring device in the unloaded
state.
[0043] FIG. 12 shows the embodiment illustrated in FIG. 11 in the
loaded state.
[0044] FIG. 13 shows a schematic representation of the function of
the embodiment shown in FIGS. 11 and 12.
DETAILED DESCRIPTION OF THE INVENTION
[0045] As can be seen in particular from FIGS. 1 to 3, in accord
with one embodiment of the invention, the dynamic anchoring element
1 is formed as a polyaxial screw. It comprises a screw element 2
with a threaded shank part 3 and a head 4 formed in one piece
therewith and a receiving part 5. The head 4 is substantially
formed in the shape of a segment of a sphere and has on its end
opposite to the shank part 3 a widened edge or collar 6, so that a
flat front face 7 is formed which has a diameter which is larger
than the diameter of the spherical segment-shaped section of the
head. A recess for bringing into engagement with a screwing-in tool
is further formed in the front face 7.
[0046] The receiving part 5 is substantially formed cylindrically
symmetric and has on one of its ends a coaxial first bore 10 the
diameter of which is larger than that of the threaded section of
the shank 3 and smaller than the spherical diameter of the
spherical segment-shaped section of the head 4. It further has a
coaxial second bore 11 which is open at the end opposite the first
bore 10 and the diameter of which is large enough for the screw
element 2 to be inserted through the open end with its threaded
section through the first bore 10 and with the spherical
segment-shaped section of the head 4 to the bottom of the second
bore. In the receiving part, adjacent to the first bore 10 a
section 12 is provided, shaped like a segment of a hollow sphere,
the radius of which is substantially identical to the radius of the
section of the spherical segment-shaped head 4. The receiving part
further has a U-shaped recess 13, extending from the open end
towards the first bore 10, the bottom of which is directed towards
the first bore 10 and by which two open legs 14 are formed, only
one of which is illustrated in the figures. An inner thread 15 is
formed in the receiving part adjacent to the open end of the legs
14. The width of the U-shaped recess 13 is minimally larger than
the diameter of a rod 100 to be received therein which connects
several such polyaxial screws. The depth of the U-shaped recess is
dimensioned in such a way that when the rod is inserted a fixing
screw 16 can be screwed in between the legs.
[0047] The section 12 of the receiving part which is shaped like a
segment of a hollow sphere is preferably polished smooth or coated
with a material which increases the sliding capacity, so the head 4
can easily be swiveled in the section 12 of the receiving part.
Alternatively, or additionally the head 4 is polished smooth or
coated.
[0048] Between the inserted rod 100 and the head 4 of the screw
element a pressure element 20 is provided. The pressure element 20
is formed in the shape of a cylinder and has a diameter which is
smaller than the inner diameter of the second bore 11 of the
receiving part and which is preferably identical to the diameter of
the front face 7 of the head. The axial length of the pressure
element 20 is slightly larger than or identical to the distance
between the front face 7 of the head 4 and the bottom of the
U-shaped recess 13 in the inserted state. The pressure element is
resilient, in the illustrated embodiment it is formed from an
elastomer, e.g., from polyurethanes or polysiloxanes. However, any
suitable biocompatible material can be used.
[0049] Between the pressure element 20 and the inserted rod 100 a
cap 21 is provided, which covers the pressure element on the side
facing the rod and which is constructed from an inflexible
material, for example a synthetic material or a body-compatible
metal. The outer diameter of the cap 21 is dimensioned in such a
way that the cap is displaceable by sliding in the second bore of
the receiving part and the inner diameter of the cap substantially
corresponds to the outer diameter of the pressure element 20 when
this is in an unloaded state. The cap overlaps the pressure element
to such an extent that the pressure element is able to expand in
the radial direction when put under load.
[0050] FIG. 1 shows the unloaded state in which the screw element
2, the pressure element 20 and the cap 21 are inserted into the
receiving part and the rod 100 is placed into the U-shaped recess
13, but the inner screw has not yet been screwed down. In this
state the side 22 of the cap 21 facing away from the pressure
element 13 is at a slightly higher position than the bottom of the
U-shaped recess 13, so that the rod rests with its lower side on
the surface 22 of the cap and thus a gap 23 is formed between the
lower side of the rod and the bottom of the U-shaped recess 13.
[0051] In operation, as shown in FIG. 1, first the screw element 2
is inserted into the receiving part 5 from the open end thereof
until the head rests against the section 12 of the receiving part
shaped like a segment of a hollow sphere. The screw element is then
screwed into the vertebra. Then, the pressure element 20 together
with the cap 21 placed thereon is inserted into the receiving part,
the receiving part is aligned and the rod inserted. Finally, the
inner screw 16 is screwed into the receiving part.
[0052] As illustrated in FIG. 2, the inner screw is screwed in
until it presses the rod against the bottom of the U-shaped recess
and thus fixes the rod. At the same time, the rod presses on the
cap 21, which serves for even distribution of the force of pressure
exerted by the rod on to the entire surface of the pressure
element. Due to the elasticity of the pressure element it is
pre-compressed via the force exerted by the rod. At the same time,
the pressure element takes on a shape curved outwards in the radial
direction, shown in FIG. 2. In the state shown in FIG. 2 the
pressure element 20 is under bias in respect of the screw head 4
and due to the return force it presses with its lower side evenly
on the front face 7 of the head. In this way, the head is pressed
against the section 12 of the receiving part.
[0053] The screw element 2 screwed into the vertebral body is moved
out of its resting position by a self-movement of the vertebral
column. When the vertebra moves towards the rod at an angle of
90.degree. to the rod axis there is uniform compression of the
pressure element and the angle of the shank relative to the
receiving part does not change. When the vertebra moves at an angle
other than 90.degree. to the rod axis, as shown in FIG. 3, there is
a swiveling of the head, which easily slides in the section 12 of
the receiving part. Thereby, the front face 7 of the screw head
exerts a compression force on to the pressure element on one side
which compresses it on one side near the edge. On the other hand,
on the opposite side, the pressure element standing under
pre-stress expands owing to the relief of pressure. Thus, the
pressure element always remains in contact with the screw head.
[0054] Due to the elasticity of the pressure element, the
compression effects a return force onto the screw head. In this
way, a movement of the vertebra back into its original position in
which it has been placed by the surgeon is supported.
[0055] By the choice of an elastomer material for the pressure
element with a desired compressibility a limitation of motion of
the vertebra can be adjusted. If the material is only slightly
compressible, the device allows only a small deflection out of the
resting position. If the material properties are changed, larger
swivel ranges are possible. Those skilled in the art can readily
substitute materials using routine experimentation. Body-compatible
elastomer can be used as elastomer material, e.g., polyurethanes or
polysiloxanes.
[0056] The swivel range can also or additionally be set by the
selection of the diameter of the collar 6 of the screw head
relative to the diameter of the second bore 11 of the receiving
part. When the collar 6 abuts on the wall of the receiving part in
the swiveled position of the screw element 2, no further swiveling
is possible.
[0057] FIG. 4 shows a pressure element 25 according to a second
embodiment. The pressure element 25 has a housing formed in a box
shape, consisting of a lower part 26 and an upper part 27, which
closes the lower part like a lid. Inside, at least two preferably
four or more helical springs 28 are arranged opposite one another
which are distanced evenly apart in the circumferential direction,
and which are connected with one of their ends to the lower part
and with their other end to the upper part. The helical springs 28
are arranged near the housing wall, as the compression forces are
greater at the edge of the pressure element than in the center, as
can be seen in FIG. 3. The strength of the helical springs is
selected in such a way that a desired or required compression via
the screw head can be achieved.
[0058] If the anchoring device comprises the pressure element
according to the second embodiment, the cap 21 described in the
first embodiment is not necessary, as the upper side of the
pressure element consists of an inflexible material.
[0059] The operation of the anchoring device is like that of the
first embodiment. In order to prevent lateral displacement of the
pressure element 25 in the receiving part, the diameter of the
pressure element is in a further modification only slightly smaller
than the diameter of the second bore 11 of the receiving part.
[0060] In a further embodiment, the pressure element itself is
formed as a helical spring. The diameter of the helical spring then
corresponds to the diameter of the box-shaped housing according to
the second embodiment. Other types of springs are also possible,
e.g., one or more spring washers.
[0061] In an alternative embodiment in the elastomeric pressure
element, helical springs are contained in an arrangement identical
to or similar to that according to FIG. 4 and are cast into an
elastomeric material during manufacture of the pressure element.
These springs then serve to support the elastic properties of the
elastomer.
[0062] In a modification of the first embodiment, the pressure
element 20 and the cap 21 are pre-mounted in the receiving part 5
and secured against falling out, e.g., by crimped bores provided in
the receiving part and countersunk bores in the pressure element
corresponding therewith. In this case the pressure element 20 and
the cap 21 have a coaxial central bore which enables a screw tool
to be guided through to screw the screw element 2 into the bone.
The bore can also be provided if the pressure element and the cap
are not pre-mounted.
[0063] In a further embodiment, the pressure element is formed in
such a way that the face facing the cap 21 and/or the front face 7
of the head is curved concavely towards the inside of the pressure
element. This, in cooperation with the flat face of the cap and/or
the screw head, creates an increase in the pressure elasticity at
the edge.
[0064] In a further modification, the head does not have the
collar, but is formed, e.g., in the shape of a semi-sphere, as
illustrated in FIG. 6, so that the front face has the largest
diameter of the screw head. It is decisive that there is a
sufficiently large front face for cooperation with the pressure
element which guarantees force transmission at the edge.
[0065] In a second embodiment of the anchoring device shown in FIG.
5a, the resting position of the screw element 2 relative to the
receiving part 5 is at an angle .alpha. to the central axis M of
the receiving part which is different from 0.degree.. In this case,
the screw element 2' is constructed in two parts. It comprises a
head 40 and a threaded shank 30 which can be connected thereto. The
threaded shank 30 has on one of its ends a thread-free section 31.
On this end there is further provided on the front a recess 32 for
bringing into engagement with a screw tool. The head 40, like that
of the screw element of the first embodiment, comprises a spherical
segment-shaped section and a collar 41 adjoining the spherical
segment-shaped section on the side facing away from the shank and
having a front face 42 for cooperating with the pressure element.
On the side facing away from the front face the head 40 has a bore
43 extending at a predetermined angle .alpha. to the axis of
symmetry of the head. The diameter of the bore is identical to the
outer diameter of the thread-free section 31 of the shank 30, so
that the shank can be inserted into the bore by friction locking.
To improve the damping effect on to the inserted shank the head can
have slits, not illustrated, in its wall, so that the bore has a
resilient edge.
[0066] Alternatively, an inner thread is provided in the bore 43
and an outer thread on the shank section 31 matching the inner
thread to allow screwing in of the shank into the head.
[0067] The remaining parts of the anchoring device are as in the
embodiment according to FIGS. 1 to 3 or its modifications.
[0068] In operation first the shank 30 is screwed into the
vertebra. Then, the receiving part 5 with its first bore 10 is
placed diagonally onto the shank 30 or onto the projecting
thread-free section 31 and then the head 40 with the pressure
element and, if applicable, the cap are inserted into the receiving
part in the pre-compressed state with a suitable tool and with the
bore 43 slid onto the shank. The longitudinal axis of the shank 30,
thus, has a predetermined angle .alpha. to the central axis of the
head 40 and therefore to the central axis of the receiving part 5.
Subsequently, the rod is inserted and finally the whole arrangement
is fixed via the inner screw 16, as in the first embodiment. Like
in the first embodiment, when the vertebra moves, the return force
causes the head to be forced back into its resting position.
Although the angle is preset by the angle of the bore 43, the
surgeon can still perform an adjustment by rotating the receiving
part about its axis or by a minimal swiveling of the head.
[0069] In a further modification of the second embodiment, the head
is constructed in one piece with the shank, but the front face of
the head which forms the support face for the elastic pressure
element is at an angle to the axis of the shank. In FIGS. 5b to 5e,
the manufacturing steps of a screw element 200 of this kind are
shown. The screw element 200 has a threaded shank 300 and a
spherical segment-shaped head 400 connected thereto in one piece.
As shown in FIG. 5b, the head is milled off in such a way that the
front face 700 has a predetermined angle to the axis of the shank.
Subsequently, as shown in FIG. 5c, a bore 701 with an inner thread
is produced, which extends perpendicular to the front face 700.
Into this bore, as shown in FIG. 5c, a screw 600 with a
collar-shaped head and with a recess 601 for subsequent screwing
into the bone is screwed into the head, the diameter of the collar
being larger than the diameter of the head 400. The finished screw
element 200, shown in FIG. 5e, is then inserted into the receiving
part.
[0070] In operation, the screw element 200 is inserted into the
receiving part and then screwed into the bone. By means of the face
700 extending at the predetermined angle to the axis of the shank
the screw element 200 has the predetermined angle relative to the
receiving part in the resting position. The insertion of the
pressure element and the rod takes place as previously
described.
[0071] The collar can also be constructed in one piece with the
screw element.
[0072] In a further modification of the second embodiment, shown in
FIGS. 10a-10c, it is not the receiving part 5 itself which
comprises the section shaped like a segment of a sphere against
which the head rests, but in the receiving part an insert 500 made
of an elastomer is provided, which is constructed with a
cylindrical outer wall and surrounds the spherical segment-shaped
section of the head laterally starting from the first bore 10, or
which, as shown in FIG. 10a, is ring-shaped and has only a support
face 501 for the screw head. Further, a rigid pressure element 502
which presses on the head 4 is provided. The pressure element 501
has a spherical segment-shaped recess which fits into the screw
head. In operation, after adjustment of the screw 2 and the
receiving part 5 in respect of one another, the screw head 4 is
pressed via the fixing screw 16 and the pressure element 502 at a
desired angle against the insert, which therein, because it is
slightly compressed, is under bias, as shown in FIG. 10b. This
position forms the resting position. When there is a movement of
the vertebra, the screw head presses against the insert 500, so
that it deforms at this point and enables the screw to move out
from the resting position, as shown in FIG. 10c. Simultaneously,
the increasing return force forces the head back into its resting
position. In this embodiment, the desired angle of the screw shank
to the receiving part, which is supposed to form the resting
position, can be freely adjusted.
[0073] In a further modification, the pressure element is formed so
as to be wedge-shaped.
[0074] In a third embodiment, shown in FIG. 6, the anchoring device
is formed in such a way that the head and the rod can be
independently loaded. For this purpose, in contrast to the first
embodiment, the pressure element 50 has a first elastic section 51
and a second inflexible section 52 adjacent thereto, which are
rigidly connected to one another. The inflexible section 52 has a
U-shaped recess 53, the dimensions of which are such that the rod
100 can be inserted therein. The depth of the U-shaped recess of
the pressure element, seen in the direction of the cylinder axis,
is greater than the diameter of the rod. The open legs 54, 55
formed by the U-shaped recess thereby project beyond the rod when
it has been inserted. Further, a nut or bushing type closing
element 56 is provided, which has an outer thread 57 cooperating
with the inner thread of the receiving part and an inner thread 58.
An inner screw 59 is provided to be screwed into the closing
element 56.
[0075] In operation, when a force is exerted on the legs of the
rigid pressure element part 52 and the elastic pressure element
part 51 via the closing element 56, a force is applied to the screw
head. The rod is fixed independently via the inner screw 59. If
desired, the rod can also be movably held. In this case, the inner
screw is screwed in only to such an extent that the rod can still
slide in the U-shaped recess of the receiving part.
[0076] In the embodiment shown, in which sections 51 and 52 are
rigidly connected to one another, the pressure element 50 is
constructed in one piece. In a modification, it is constructed in
two pieces and then consists of an elastic part 51 according to the
embodiment according to FIG. 1 and a non-elastic part 52, which has
the U-shaped recess.
[0077] FIG. 7 shows a dynamic stabilization device for vertebrae
according to a first embodiment. This is, in particular, applicable
in a case in which an intervertebral disc or a vertebra is removed
and replaced by a rigid fusion element 60, e.g., a tube-shaped
implant with openings in the wall and, e.g., filled with bone mass
to allow bones to grow in.
[0078] The stabilization device comprises two dynamic bone
anchoring devices 1, 1' in the posterior area, which are connected
to one another via a rigid rod 100. Each of the bone anchoring
devices 1, 1' is formed according to one of the previously
described embodiments. Because of the elastic construction of the
pressure element and the associated damping effect there is
intermittent, limited load onto the fusion element 60, resulting in
acceleration of the growing in of bone in and around the fusion
element. This accelerates the healing process.
[0079] FIG. 8 shows a dynamic stabilization device for vertebrae
according to a second embodiment. This can be applied in particular
in a case in which an intervertebral disc has been removed and
replaced by an intervertebral disc prosthesis 61. The stabilization
device comprises two dynamic anchoring devices 101, 101' which are
connected to one another via a rigid rod 100. At least one of the
anchoring devices 101, 101' is formed according to the embodiment
shown in FIG. 6, which is characterized in that pressure is exerted
on the screw head via the pressure element 50, but the rod still
remains displaceable in the axial direction. The stabilization
device further comprises a spring element 102 provided on the rod
between the two anchoring devices, and also at least one stop 103
on the rod arranged on the side opposite to that spring element 102
of the anchoring device in which the rod 100 is held slidingly. In
the example shown in FIG. 8, two such stops are provided and the
rod is slidingly held in both anchoring devices 101, 101'. The
spring element 102 is inserted in between the anchoring devices
under bias and thus acts as extension spring.
[0080] In operation, the combination of posterior longitudinal
resiliency of the rod 100 and the polyaxial damping of the
anchoring devices 101, 101' enables control of movement and
relieving of the stress on the intervertebral disc prosthesis. The
stabilization device can be applied for any artificial
intervertebral disc structure.
[0081] FIG. 9 shows a further application of the stabilization
device illustrated in FIG. 8, which comprises the extension spring
rod and the dynamic anchoring devices in the form of the previously
described polyaxial damping screws in the posterior area. In this
case of application, the human intervertebral disc is damaged to an
extent that, when relieved from stress, it will recover. The
stabilization device therein relieves the stress on the human
intervertebral disc and, at the same time, limits the extent of
movement, so that extreme movements, which would further damage the
intervertebral disc, cannot occur and the intervertebral disc is
able to recover in the resting phase, e.g., at night or while lying
down.
[0082] In FIGS. 11 to 13, a further embodiment of the invention is
described. Elements which are corresponding to the elements of the
embodiment shown in FIGS. 1 to 3 have the same reference numerals.
According to FIG. 11, this embodiment comprises in addition to the
elastic pressure member 20, which is arranged between the rod and
the head, a second elastic pressure member 600. The second pressure
member 600 is ring-shaped and arranged such that it encompasses the
screw head at the location where the collar 6 is formed adjacent to
the spherical segment-shaped section. In the embodiment shown, the
second pressure member 600 is formed as O-ring. The outer diameter
of the pressure member and its inner ring diameter are dimensioned
such that in the unloaded state shown in FIG. 11 in which the
pressure member is inserted into the receiver member 5, the ring is
in contact with the outer side of the head and the inner wall of
the receiver member. Suitably, at the time of inserting of the
screw element into the receiver member the second pressure member
600 is already placed on the screw head.
[0083] In operation, in the loaded state shown in FIG. 12 in which
the rod is fixed, the pressure member 600 is deformed. Due to the
compression occurring when the pressure element is deformed, the
pressure element is spring-biased towards the screw head. According
to FIG. 13, the first pressure member 20 causes a return force
acting upon the front face 7 of the screw head from the top, which
is represented by the arrow F.sub.1, when the screw element 2 moves
out of its resting position, whereas the second pressure member 600
generates a return force, illustrated by arrow F.sub.2, on the
screw head acting from laterally below the front face 7 and being
diagonally offset with respect to the force F.sub.1. Therefore,
return forces acting upon the screw head which return the latter
into its original position as shown by the arrow A in FIG. 13 are
increased by means of the second pressure member 600. In addition,
the second pressure member 600 reduces wear of the first pressure
member 20.
[0084] By selection of the materials of the first pressure member
20 and the second pressure member 600, which can be different, a
desired adjustment of the damping can be achieved. For instance,
the first pressure member is formed of a harder or less
compressible material than the second pressure member.
[0085] In a modification of this embodiment, the second pressure
element is not formed as O-ring but as a molded ring.
[0086] The invention is not limited to the above-described
embodiments. Combinations of elements of the individual embodiments
with elements of other embodiments are possible. In particular, the
invention is also not confined to a polyaxial screw. For example, a
hook can also be provided as anchoring element instead of the
threaded shank. The receiving part can also be constructed in such
a way that the screw can be inserted from below into the receiving
part. In this case, a molded ring is provided as end stop for the
screw head.
[0087] The section 12 of the receiving part which supports the head
is not restricted to have a spherical shape, it can also be conical
or can have another shape suitable for the particular
application.
[0088] In a stabilization device using the anchoring device
according to the embodiments described above, a force acting on the
rod due to a movement of the bone segment or the vertebra in which
the anchoring device is anchored is prevented from being fully
transmitted to the area where the shank is anchored. Thus,
loosening of the shank in the bone can be reduced or prevented.
[0089] Those persons skilled in the art easily recognize that the
invention is not limited to a dynamic anchoring device wherein the
screw element is inserted from above in the receiving part, but is
also applicable to a dynamic anchoring device wherein the screw
element can be inserted from below through the bore.
* * * * *