U.S. patent application number 12/764442 was filed with the patent office on 2010-08-12 for dynamic stabilization device for bones, in particular for vertebrae.
This patent application is currently assigned to Biedermann Motech GmbH. Invention is credited to Lutz Biedermann, Dezso Jeszensky.
Application Number | 20100204736 12/764442 |
Document ID | / |
Family ID | 30128808 |
Filed Date | 2010-08-12 |
United States Patent
Application |
20100204736 |
Kind Code |
A1 |
Biedermann; Lutz ; et
al. |
August 12, 2010 |
DYNAMIC STABILIZATION DEVICE FOR BONES, IN PARTICULAR FOR
VERTEBRAE
Abstract
A dynamic stabilization device for bones, in particular
vertebrae, is made with two bone anchoring elements and a rigid rod
with a longitudinal axis connecting them. An elastic element is
inserted between the two bone anchoring elements. It acts on the
bone anchoring elements to exert a force in a direction of the
longitudinal axis. Each bone anchoring element has a first section
to be anchored in a bone and a second section to be connected to
the rod. At least one of the bone anchoring elements is fixedly
connected to the rod to prevent translational movement of the rod
relative to it. Further, at least one of the bone anchoring
elements is a polyaxial bone screw. Also disclosed is a method for
stabilizing vertebrae adjacent to a defective intervertebral disc.
A dynamic stabilization device is provided. The anchoring elements
are attached to two vertebrae on opposite sides of the defective
intervertebral disc. Then, the bone anchoring elements are alligned
to connect the rod therebetween with the elastic element positioned
between the bone anchoring elements. Finally, one of the bone
anchoring elements is connected fixedly to the rod to prevent
translational movement of the rod relative to it.
Inventors: |
Biedermann; Lutz;
(VS-Villingen, DE) ; Jeszensky; Dezso; (St.
Gallen, CH) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Assignee: |
Biedermann Motech GmbH
|
Family ID: |
30128808 |
Appl. No.: |
12/764442 |
Filed: |
April 21, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10637349 |
Aug 7, 2003 |
7722649 |
|
|
12764442 |
|
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|
|
Current U.S.
Class: |
606/264 |
Current CPC
Class: |
A61B 17/7008 20130101;
A61B 2017/00845 20130101; A61B 17/7032 20130101; A61B 17/7035
20130101; A61B 17/702 20130101 |
Class at
Publication: |
606/264 |
International
Class: |
A61B 17/70 20060101
A61B017/70 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2002 |
DE |
102 36 691.8 |
Claims
1. A dynamic stabilization device for bones, said device
comprising: a first bone anchoring element; a second bone anchoring
element; a rod having a longitudinal axis connecting the two bone
anchoring elements; and an elastic element between the first and
the second bone anchoring element and acting on the first and the
second bone anchoring elements to exert a force in a direction of
the longitudinal axis; each bone anchoring element comprising a
first section to be anchored in a bone and a second section to be
connected to the rod; at least one of the bone anchoring elements
comprising a polyaxial bone screw.
2. The dynamic stabilization device according to claim 1, wherein
the rod is a rigid rod.
3. The dynamic stabilization device according to claim 1, wherein
at least one of the bone anchoring elements is fixedly connected to
the rod so as to prevent translational movement of the rod relative
to the at least one of the bone anchoring elements.
4. The dynamic stabilization device according to claim 1, wherein
one of the bone anchoring elements is slideably connected to the
rod and wherein the device further comprises a stop to limit the
movement of the slideably connected bone anchoring element.
5. The dynamic stabilization device according to claim 1, at least
one of the bone anchoring elements comprising a polyaxial bone
screw wherein the first section comprises a shank with a second
longitudinal axis for anchoring in the bone and the second section
comprises a receiving part with a cylindrical axis, the receiving
part being connected in an articulated manner to the shank for
receiving the rod, and wherein the shank and the receiving part can
be fixed relative to one another at an angle between the second
longitudinal axis and the cylindrical axis.
6. The dynamic stabilization device according to claim 1, further
comprising a stop, wherein the polyaxial bone anchoring element is
slideably connected to the rod and located adjacent to the stop to
limit the movement thereof.
7. The dynamic stabilization device according to claim 1, wherein
the rod is coated with a material having a low coefficient of
friction.
8. The dynamic stabilization device according to claim 6, wherein
the material is a high molecular weight polyethylene.
9. The dynamic stabilization device according to claim 1, wherein
one of the bone anchoring elements comprises a material having a
low coefficient of friction for contacting the rod.
10. The dynamic stabilization device according to claim 7, wherein
the material is a high molecular weight polyethylene.
11. The dynamic stabilization device according to claim 1, wherein
the elastic element comprises a spring.
12. The dynamic stabilization device according to claim 1, wherein
the elastic element comprises a helical spring that is located
around the rod.
13. The dynamic stabilization device according to claim 1, wherein
the rod comprises two sleeve-shaped sections and the elastic
element comprises a spring positioned inside the two sleeve-shaped
sections.
14. The dynamic stabilization device according to claim 1, wherein
each of the bone anchoring elements comprise a bone screw or a bone
hook.
15-27. (canceled)
Description
FIELD OF THE INVENTION
[0001] The invention relates to a dynamic stabilization device for
bones, in particular for vertebrae, preferably with at least one
first and one second bone anchoring element, and a rod connecting
the bone anchoring elements, wherein each bone anchoring element
has a first section to be anchored in a bone and a second section
to be connected to a rod, and wherein the bone anchoring elements
can optionally be connected to the rod rigidly or as displaceable
in the direction of the shaft of the rod.
BACKGROUND OF THE INVENTION
[0002] A known method for treating intervertebral disc defects is
removal by operation of the defective intervertebral disc and
stiffening the intervertebral disc space with two vertebral bodies
or, after removal of the defective intervertebral disc, subsequent
insertion of an artificial intervertebral disc. In the first case,
the sections of the vertebral column adjacent to the stiffened
section are unnaturally stressed and, in the second case,
simulation of the properties of a natural intervertebral disc is
still unsatisfactory.
[0003] EP 0 669 109 B1 describes a device for stabilizing adjacent
thoracic vertebrae, with which a damaged intervertebral disc and
the intervertebral joints can be partly relieved from stress
posteriorly. The device has two pedicle screws, which are rigidly
connected in each case to a band consisting of an elastic synthetic
material and are connected to one another via the biased band. To
transmit pressure forces, a compression-proof body pushed on to the
elastic band is further provided between the two screw heads. The
use of a band of this kind does not however produce any guidance
stability of the movement segment of a vertebral column. Nor is it
possible to adjust the adjacent vertebrae in their positioning
relative to one another, because the force transmission behaviour
of the band and the pressure element via the bone screws is
non-specific.
[0004] EP 0 518 567 B1 describes a device for stabilizing adjacent
vertebrae, which has a damping element consisting of an elastomer,
which is provided between two monoaxial screws screwed into the
vertebrae. Each end of the damping element is connected a spherical
head of the bone screw, which can be inserted into a receiving part
of the bone screw and fixed therein. Thus, a minimal adjustment of
the angle of the bone screw relative to the longitudinal axis of
the damping element is possible. However, for each pair of
vertebrae to be connected to one another an individually matching
damping element with exact length and exact cross-section has to be
made. Furthermore, the force transmission behaviour of the damping
element is undefined, as it yields not only to axial, but also to
bending and torsional forces.
[0005] It is further known to provide for fixing the vertebral
column or sections of the vertebral column with an implant system
consisting of a rod and at least two pedicle screws rigidly
connected to the rod and screwed into corresponding vertebrae.
However, with this implant system it is not possible to provide for
dynamic movement control of the intervertebral disc or for dynamic
takeover of stress to relieve the stress on a intervertebral
disc.
[0006] U.S. Pat. No. 5,672,175 describes a dynamic implanted spinal
orthosis which attempts to preserve at least in part the natural
mobility of the vertebrae while effecting and maintaining a
correction of the relative positions of the vertebrae without
osteosynthesis, graft or fusion. As such, anchoring components are
fixed to the vertebrae, each anchoring component comprising at
least one plate having an anterior convex face coming to bear in
contact with the vertebral lamina on at least one side of the
spinous process. Cylinders of the coupling means are carried by a
plate opposite the transverse end of the lamina near the transverse
process. Each plate is fixed to a vertebrae on at least two
different places, for example, by an intrapedicular screw and/or
clamping hooks. Holding means are coupled to the plates, the
holding means comprising an elastic return device for exerting
forces for holding the vertebrae in the corrected position against
natural deforming forces, thus treating a deformation of the
spine.
[0007] U.S. Pat. No. 5,733,284 describes a device for anchoring
rachidian instrumentation on a vertebrae. The device has structure
very similar to the device described in U.S. Pat. No.
5,672,175.
[0008] It is still desirable to provide new and better dynamically
acting stabilization devices for bones, in particular for adjacent
vertebrae, with which it is possible both to position the bones or
vertebrae and intervertebral joints in respect of one another and
simultaneously, in a defined way, to support and partially relieve
the stress on the intervertebral disc and intervertebral joints
connected in between with respect to the forces to be
transmitted.
SUMMARY OF THE INVENTION
[0009] The present invention provides a dynamic stabilization
device for bones, in particular for vertebrae. In accord with the
present invention, a dynamic stabilization device comprises two
bone anchoring elements and a rod connecting them. Each bone
anchoring element has a first section to be anchored in a bone and
a second section to be connected to the rod. Optionally, each bone
anchoring element can be connected to the rod rigidly or in such
manner that it is displaceable in the direction of the longitudinal
axis of the rod. An element is arranged between the bone anchoring
elements, which can be elastically biased in the direction of the
longitudinal axis of the rod.
[0010] In one embodiment of the invention, one of the bone
anchoring elements preferably is connected displaceably to the rod
and a stop, which is provided to limit the movement of the
displaceable bone anchoring element.
[0011] In another embodiment, at least one bone anchoring element
preferably is connected polyaxially to the rod.
[0012] In a further embodiment of the invention, the bone anchoring
element has a shank for anchoring in the bone and a receiving part
that is connected in an articulated manner to the shank for
receiving the rod. Preferably, the shank and the receiving part are
fixed relative to one another in an angle independently of fixing
of the rod. In addition, the polyaxial bone anchoring element
preferably is arranged displaceably connected to the rod and
adjacent to the stop.
[0013] In certain preferred embodiments of the invention, at least
one of the bone anchoring elements is rigidly connected to the
rod.
[0014] In still another embodiment of the invention, the rod and/or
parts of one of the bone anchoring elements is/are coated with a
sliding material (a material having a low coefficient of
friction).
[0015] In embodiments of the invention having an elastically biased
element arranged between the bone anchoring elements, preferably
the elastically biased element comprises a spring. More preferably,
the elastically biased element comprises a helical spring, which
surrounds the rod.
[0016] In further embodiments of the invention, the rod comprises
two pieces comprising a sleeve and the spring is provided inside
the rod.
[0017] Typically, the bone anchoring elements are constructed as
bone screws or bone hooks.
[0018] The invention also provides a method for stabilizing
vertebrae adjacent to a defective intervertebral disc. The method
comprises the following steps: providing a dynamic stabilization
device comprising a first bone anchoring element, a second bone
anchoring element, a rigid rod having a longitudinal axis
connecting the two bone anchoring elements and an elastic element
between the first and the second bone anchoring element and acting
on the first and the second bone anchoring element to exert a force
in a direction of the longitudinal axis, wherein each bone
anchoring element comprises a first section to be anchored in a
bone and a second section to be connected to the rod, and wherein
at least one of the bone anchoring elements comprising a polyaxial
bone screw; attaching the first and second bone anchoring elements
to two vertebrae on opposite sides of the defective intervertebral
disc; aligning the second section of both of the first and second
bone anchoring elements to connect the rod therebetween with the
elastic element positioned between the first and second bone
anchoring elements; and fixedly connecting at least one of the bone
anchoring elements to the rod so as to prevent translational
movement of the rod relative to the at least one of the bone
anchoring elements.
[0019] Further features and advantages of the invention will become
apparent from the detailed description and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows a schematic side view of the device according
to the invention in an assembled state in vertebrae.
[0021] FIG. 2 shows a horizontal projection on to the device as
illustrated in FIG. 1.
[0022] FIG. 3 shows a sectional illustration of a polyaxial screw
used in the device taken along line A-A in FIG. 1.
[0023] FIG. 4 shows an illustration in partial section of a
polyaxial screw illustrated in FIG. 1 taken along the line B-B in
FIG. 2.
[0024] FIG. 5 to FIG. 8 illustrate a sequence of steps showing the
assembly of the stabilization device in vertebrae.
DETAILED DESCRIPTION OF THE INVENTION
Including Preferred Embodiments
[0025] The invention is now described in detail with reference to
the embodiment illustrated in FIGS. 1 to 4. A stabilization device
in accord with one embodiment of the present invention has two
polyaxial pedicle screws 1, 2 and a rod 3 connecting them for
stabilizing two adjacent vertebrae 100, 101. The stabilization
device further contains a spring element 30, provided between the
two pedicle screws.
[0026] The pedicle screws 1, 2 preferably are constructed as
illustrated in FIGS. 3 and 4. A pedicle screw 1, 2 has a screw
element with a threaded shank 4 with a bone thread and a head 5
shaped like a segment of a sphere, which is connected to a
receiving part 6. The receiving part 6 has on one of its ends a
first bore 7, aligned symmetrically to the axis, the diameter of
which is larger than that of the threaded section of the shank 4
and smaller than that of the head 5. It further has a coaxial
second bore 8 which is open at the end opposite the first bore 7
and the diameter of which is large enough for the screw element to
be guided through the open end with its threaded section through
the first bore 7 and with its head 5 as far as the floor of the
second bore. The floor of the receiving part is constructed in such
a way that the screw element in the inserted and unstressed state
is swivellable in the receiving part 6. The receiving part further
has a U-shaped recess 61 shown in FIG. 4 which is arranged
symmetrical towards the center and the floor of which is directed
towards the first bore 7 and by which two open legs 10, 11 are
formed. In an area bordering on the open end the legs 10, 11 have
an inner thread 12.
[0027] The pedicle screw additionally contains a pressure element
13, which is constructed with a suitable outer diameter in such a
way that it can be pushed into the receiving part 6. On one of its
ends a recess 14 is provided, shaped like a segment of a sphere and
widening towards the first bore 7 of the receiving part 6, and the
spherical radius of which is chosen in such a way that in a state
inserted into the receiving part it surrounds the head 5 of the
screw element. In the direction of the open end of the legs 10, 11
the pressure element 13 has a U-shaped recess 15, the dimensions of
which are so dimensioned that the rod 3 can be placed into the
thereby formed channel. The depth of the U-shaped recess 15, seen
in the direction of the cylindrical axis of the receiving part 6,
is greater than the diameter of the rod 3 to be received, so the
pressure element 13 projects upwards with lateral legs 16 above the
placed in rod 3. The pressure element 13 further has a central bore
17 which extends through it to permit a screw tool to engage a
corresponding recess 18 provided in the head 5.
[0028] For fixing the screw element in the receiving part a
bushing-type or nut-type locking element 20 is provided which can
be screwed in between the legs 10, 11 and which has an outer thread
21 which cooperates with the inner thread 12 of the legs and
further has an inner thread 22. For screwing in, the locking
element 20 further has radially running indents 23 on one of its
ends. The dimensions of the locking element 20 in the axial
direction of the receiving part and the dimensions of the open legs
10, 11 of the receiving part and the dimensions of the cooperating
threads or the height of the open legs 16 of the pressure element
are dimensioned in such a way that in the screwed in state the
locking element 20 exerts a force on the legs 16 of the pressure
element, so it blocks the head 5 in the receiving part 6. Thus, the
angle of the cylindrical axis of the receiving part relative to the
longitudinal axis of the screw element can fixed variably
[0029] Furthermore, an inner screw or clamping or setting screw 25,
which can be screwed into the locking element 20 is provided, the
outer thread 26 of which cooperates with the inner thread 22 of the
locking element 20. The dimensions of the inner screw 25, the
locking element 20 and the pressure element 13 are chosen in such a
way that in the screwed in state the inner screw 25 presses on the
placed in rod 3.
[0030] FIG. 4 shows a section through the pedicle screw 1 according
to FIGS. 1 and 2. Pedicle screw 1 differs from pedicle screw 2 in
the construction of the inner screw. As can be seen from FIG. 4,
the inner screw 25' of the pedicle screw 1 has on its side facing
the rod a sliding floor 26 made of a sliding material in order to
enable low-friction sliding of the rod in operation.
[0031] A high molecular weight polyethylene of the UHM WPE type
with a molecular weight between 2.times.10.sup.6 to
10.times.10.sup.6 is used, for example, as sliding material. Other
biocompatible materials having low coefficient of friction can also
be used. Such materials are well known to those skilled in the
art.
[0032] The spring element 30 preferably is constructed as a helical
spring with a diameter which is slightly larger than the diameter
of the rod 3, so the helical spring can be pushed on to the rod 3.
The length of the helical spring in the axial direction is matched
to the size of the distance between the adjacent vertebrae to be
bridged by the rod between the two pedicle screws. Furthermore, the
length of the helical spring and the spring force can be selected
by the surgeon and are dimensioned in such a way that an extension
or compression effect can be achieved with the spring for an
existing functional deficit of the intervertebral disc. The spring
is preferably coated with an abrasion-proof material, e.g. with an
abrasion-proof synthetic material
[0033] The rod 3 preferably has a stop 31 on one of its ends, e.g.
in the form of a ring-shaped shoulder, which has a diameter which
is larger than the diameter of the U-shaped recess of the receiving
part 6 and the pressure element 13 so that, in the assembled state,
the pedicle screw 1 adjacent to the stop 31 is displaceable along
the rod only as far as the stop.
[0034] Preferably, the rod is coated with a material, in
particular, with a suitable material having a low coefficient of
friction, which facilitates sliding of the rod in the receiving
part 6 or in the pressure element 13 provided for this. Preferably,
the pressure element 15 of at least one of the pedicle screws also
is coated with a material having a low coefficient of friction
which increases the ability to slide, e.g. a synthetic
materialSuitable materials include, for example, UHM WPE or
anodized metal, such as anodized titanium.
[0035] In operation, as can be seen from FIG. 5, first the screw
elements of the pedicle screws 1, 2, which have been inserted into
the receiving parts 6, are screwed by the surgeon into the
vertebrae of a patient adjacent to a defective intervertebral disc
200 in the unstressed state and the receiving parts 6 are aligned
in such a way that the rod 3 can be inserted into the U-shaped
recesses in the receiving parts 6. The pressure elements 13 can be
pre-assembled into the receiving parts and access to the screw head
through bore 17 to insert the screws into the vertebrae.
Alternatively, the pressure elements can be inserted after the
screws have been inserted into the vertebrae. Next, as shown in
FIG. 6, the rod 3 is inserted into the receiving parts 6 with the
spring 30 assembled on to it. The rod 3 preferably is oriented
therein in such a way that the stop 31 points in the direction of
the patient's head. Further, the spring 30 is pre-compressed by
means of a tool, in order to bring it between the two receiving
parts 6 at a bias.
[0036] In the next step, illustrated in FIG. 7, the surgeon sets
the optimum angle of screw element to receiving part or rod for
each of the pedicle screws 1, 2. This angle is then fixed by
screwing the locking elements 20 into the receiving parts. As can
be seen from FIGS. 3 and 4, fixing of the angle takes place in that
the locking element 20 exerts a force on the pressure element 13 in
such a way that it fixes the head 5 in its position in the
receiving part such that the angle between the longitudinal axis of
the screw and the cylindrical axis of the receiving head is fixed
as desired by the surgeon. Because the legs 16 of the pressure
element project beyond the placed in rod 3, the rod 3 is not
touched by screwing in the locking element 20 and is still freely
displaceable in the receiving part 6 in each case.
[0037] By means of the angle of the screw element and the receiving
part to one another a desired wedge angle can be set between the
opposite surfaces of the adjacent vertebrae, which enables the
intervertebral disc located in between to adopt its natural shape
again. By using two stabilization devices in each case, as shown in
FIG. 2, the setting of the angle is therein possible in lateral and
front view independently of one another. In this way the position
of the intervertebral joints to one another also can be
defined.
[0038] As can be seen further from FIG. 7, the spring 30 inserted
under bias expands after insertion and, thus, presses apart the two
receiving parts 6 connected by the rod. The expansion is limited on
one side by the stop 31. The expansion pressure of the spring
causes a widening out of the intervertebral space and the
intervertebral joints to take place, whereby the intervertebral
disc 200 can expand owing to absorbing fluid from the
intervertebral space and the intervertebral joints are freed from
stress, as depicted by the arrows in FIG. 7. A damaged
intervertebral disc can thus adopt its natural shape again.
[0039] As shown in FIG. 8, the spring then is compressed slightly
by moving the receiving parts 6 towards one another in order to
bring it under bias again. Thereby, the intervertebral space is
also reduced and the intervertebral disc is pressed together or
shortened slightly again and the intervertebral joints are
stressed, as illustrated by the arrows in FIG. 8. In the desired
final position, the rod 3 is rigidly connected to the receiving
part 6 of the pedicle screw positioned at the end of the rod 3
opposite the stop 31. Fixing the rod takes place by screwing in the
inner screw 25 in the receiving part of the lower pedicle screw 2.
However, in the pedicle screw 1 provided adjacent to the stop 31 of
the rod the receiving part 6 and the rod 3 remain movable (i.e.,
longitudinally displaceable) with respect to one another. The inner
screw 25' with the sliding floor 26 enables low-friction sliding of
the rod.
[0040] In the position shown in FIGS. 1 and 2, the dynamic
stabilization system in accord with the invention acts as a force
transmission and damping system. The forces acting on the vertebral
column when the patient is in an upright position are partially
transmitted via the system consisting of pedicle screws, spring and
rod, so that the stress on the intervertebral disc is lowered. The
spring further acts both as an extension element for widening out
the intervertebral space in the resting or unstressed state, i.e.,
while lying down, and as a damper for damping jolts during
stresses, such as when walking, for example.
[0041] The system has the advantage that optimum adjustment of the
bone screws and the rod is possible during assembly. Owing to the
rigid connection via the rod, it is possible to transmit axial
forces and thus relieve the stress on the intervertebral disc. The
system is, however, rigid to bending and torsion, comprising a
further advantage in respect of precise force transmission on to
the intervertebral disc.
[0042] The invention is not limited to the connection of only two
polyaxial pedicle screws by a rod. If required, several vertebrae
can also be connected to one another, wherein a corresponding
number of polyaxial bone screws are placed in each vertebrae being
connected. Depending on the desired mobility, a stop is provided at
a suitable point on the rod and a corresponding adjacent bone screw
held in a manner displaceable relative to the rod.
[0043] Although polyaxial bone screws are used in the embodiment
example described, the invention is not limited to these. If the
anatomy of the corresponding section on the vertebral column allows
monoaxial bone screws to be used, the invention also can be used to
connect one monoaxial bone screw rigidly to the rod and one
monaxial bone screw slideably to the rod. Combinations of monaxial
bone screws and polyaxial bone screws also can be used.
[0044] The invention has been described in detail with reference to
the preferred embodiments. However, those skilled in the art, upon
consideration of the disclosure and drawings, may make
modifications and improvements within the intended scope of the
invention as defined by the claims. For example, the spring element
30 can also be constructed differently. The spring element 30 can
be constructed as a helical spring, provided inside the rod. For
this purpose the rod is formed in two parts from two sleeves
inserted into one another, each of which has a sleeve floor against
which the ends of the helical spring rest
* * * * *