U.S. patent application number 13/614325 was filed with the patent office on 2013-03-14 for modular system for the stabilization of the spinal column.
This patent application is currently assigned to Biedermann Technologies GmbH & Co. KG. The applicant listed for this patent is Lutz Biedermann, Berthold Dannecker, Wilfried Matthis, Martin Pabst. Invention is credited to Lutz Biedermann, Berthold Dannecker, Wilfried Matthis, Martin Pabst.
Application Number | 20130066375 13/614325 |
Document ID | / |
Family ID | 40185075 |
Filed Date | 2013-03-14 |
United States Patent
Application |
20130066375 |
Kind Code |
A1 |
Biedermann; Lutz ; et
al. |
March 14, 2013 |
MODULAR SYSTEM FOR THE STABILIZATION OF THE SPINAL COLUMN
Abstract
A modular system for stabilization the spinal column or other
bones includes a first stabilization element, a second
stabilization element to be connected to the first stabilization
element, and an outer connection element to connect the first
stabilization element to the second stabilization element. An end
portion of the first stabilization element and an end portion of
the second stabilization element each include a structure engaging
with a corresponding structure provided in the outer connection
element to establish a form-fit connection.
Inventors: |
Biedermann; Lutz;
(VS-Villingen, DE) ; Matthis; Wilfried; (Weisweil,
DE) ; Pabst; Martin; (Donaueschingen, DE) ;
Dannecker; Berthold; (St. Georgen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Biedermann; Lutz
Matthis; Wilfried
Pabst; Martin
Dannecker; Berthold |
VS-Villingen
Weisweil
Donaueschingen
St. Georgen |
|
DE
DE
DE
DE |
|
|
Assignee: |
Biedermann Technologies GmbH &
Co. KG
|
Family ID: |
40185075 |
Appl. No.: |
13/614325 |
Filed: |
September 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12540267 |
Aug 12, 2009 |
|
|
|
13614325 |
|
|
|
|
61088274 |
Aug 12, 2008 |
|
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Current U.S.
Class: |
606/260 ;
29/428 |
Current CPC
Class: |
A61B 17/7004 20130101;
A61B 17/7005 20130101; A61B 17/7031 20130101; A61B 17/7032
20130101; Y10T 29/49826 20150115; A61B 17/7037 20130101; A61B
17/701 20130101; A61B 17/7007 20130101 |
Class at
Publication: |
606/260 ;
29/428 |
International
Class: |
A61B 17/70 20060101
A61B017/70; B23P 11/00 20060101 B23P011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 12, 2008 |
EP |
08 014 379.5 |
Claims
1-42. (canceled)
43. Modular stabilization system for the stabilization of the
spinal column or other bones including a first stabilization
element (2); a second stabilization element (2', 5, 6, 7) to be
connected to the first stabilization element (2); an outer
connection element (4a,4b;400a,400b;500a,500b) to connect the first
stabilization element to the second stabilization element; wherein
an end portion of the first stabilization element and an end
portion of the second stabilization element each comprise a
structure (23) engaging with a corresponding structure (44,
404,504) provided in the outer connection element to establish a
form-fit connection.
44. The system according to claim 43, further comprising at least
one bone anchor (8,8'), comprising a shaft to be anchored in the
bone and a receiving part (9,9',90) for receiving the end portions
of the first stabilization element and the second stabilization
element and a securing device (13) for securing the first and the
second stabilization element in the receiving part.
45. The system according to claim 44, wherein the outer connection
element (4a,4b;400a,400b;500a,500b) is integrated in the receiving
portion (9,9') or is inserted into the receiving portion.
46. The system according to one of claims 43, wherein at least the
first stabilization element (2,2',2'',2''',20,200) is flexible.
47. The system according to claim 46, wherein the stabilization
element is made of an elastomer.
48. The system according to one of claims 43, wherein the second
stabilization element (5,6,7) is made of a rigid material, such as
a bio-compatible metal or a rigid plastic material.
49. The system according to one of claims 43, wherein an inner
connection element (3) is provided which connects the first
stabilization element to the second stabilization element.
50. The system of claim 49, wherein the inner connection element
(3) is rigid.
51. The system according to claim 49, wherein the inner connection
element is rod-like shaped and engages in respective bores (21) at
the end portions of the first and the second stabilization
element.
52. The system according to one of claims 43, wherein the structure
(32,44) comprises rib-shaped projections (23) and/or coaxial bores
(21) with undercuts (22).
53. The system according to one of claims 43 wherein the
stabilization elements are rod-shaped.
54. The system according to one of claims 43, wherein the length of
a flexible stabilization element (2,2') is designed such that only
one single motion element of the spinal column can be bridged with
the stabilization element.
55. The system according to one of claims 43, wherein the outer
connection element (4a,4b;400a,400b;500a,500b) consists of two
complementary halves each having the structure for engagement with
the structure of the stabilization element.
56. A method for manufacturing a stabilization system for the
spinal column, the method comprising assembling at least two
stabilization elements of the modular system of claim 43.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/540,267, filed Aug. 12, 2009 which claims
the benefit of U.S. Provisional Patent Application Ser. No.
61/088,274, filed Aug. 12, 2008, the contents of which are hereby
incorporated by reference in their entirety, and claims priority
from European Patent Application EP 08 014 379.5, filed Aug. 12,
2008, the contents of which are hereby incorporated by reference in
their entirety.
BACKGROUND
[0002] The invention relates to a modular system for the
stabilization, in particular for the dynamic stabilization, of the
spinal column.
[0003] A stabilization system including one or more bone screws and
a connector for traversing a space between one or more bony
structures is known from US 2007/0270821 A1. In one embodiment the
connector consists of a sequential connection of elastic and
inelastic components, which can be connected to each other, for
example, by a threaded connection, a snap-fit connections, a
quick-connect connection or other interlocking connections. The
flexible connector can be connected to the vertebrae of the spinal
column, for example, by pedicle screws.
[0004] A rod-shaped implant element for the application in spine
surgery or trauma surgery and the stabilization device with such a
rod-shaped implant element, which has rigid end portions and a
flexible middle portion is known from EP 1 757 243 A1.
[0005] EP 1 527 742 A1 describes a closure device for a pedicle
screw which fixes a single elastic rod-element in a form-fit
manner.
[0006] Based on the above, there is a need to provide a modular
system for the stabilization of the spinal column, which is
adaptable to the individual anatomic conditions and requirements of
the patient.
SUMMARY
[0007] The system of the disclosure includes a combination of a
plurality of rigid and/or flexible stabilization elements which
form a rod-like stabilization member and bone anchors to connect
the stabilization member to the vertebrae of the spinal column.
[0008] The requirements for a stabilization system of the spinal
column may be different from one motion segment to another motion
segment in terms of the desired rigidity or stability and/or in
terms of geometry such as the length of the segment and the angular
position of the vertebrae with respect to each other.
[0009] The system of the disclosure has the advantage that specific
stabilization elements can be combined according to the conditions
at the operation site. This can be done, for example, by the
surgeon during surgery.
[0010] The system of the disclosure allows to combine stabilization
elements having different characteristics such as rigid and
flexible, different materials or different degrees or orientation
of flexibility. The elements can be combined outside the patient's
body and after connection of the elements the system can be
inserted in bone anchors. Since the elements have a length which is
short compared to long elastomer rods extending over several motion
segments, the manufacturing of the elements is simplified.
[0011] The stabilization elements are fixed in bone anchors, such
as pedicle screws, at their respective end portions, which permits
to use the largest portion of the flexible elements for flexion or
extension. The stabilization elements can also be connected to each
other with a connection element at a location between two bone
anchors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a perspective exploded view of an embodiment of
the modular system.
[0013] FIG. 2 shows a perspective view of a flexible stabilization
element of the system according to one embodiment.
[0014] FIG. 3 shows a sectional view along the longitudinal axis of
the flexible stabilization element according to FIG. 2.
[0015] FIG. 4 shows a perspective view of an inner connection
element for connecting two flexible stabilization elements
according to FIG. 2.
[0016] FIG. 5 shows a side view of the inner connection element of
FIG. 4.
[0017] FIG. 6 shows a front view of the inner connection element of
FIG. 4.
[0018] FIG. 7 shows an embodiment of an outer connection element
for connecting two stabilization elements of the system.
[0019] FIG. 8 shows a sectional view along the cylinder axis of the
outer connection element of FIG. 7.
[0020] FIG. 9 shows a front view of the connection element of FIG.
7.
[0021] FIG. 10 shows a side view of a locking element for
connecting the two halves of the outer connecting element.
[0022] FIG. 11 shows a front view of the outer connection element
connecting two stabilization elements seen from the end of one
stabilization element.
[0023] FIG. 12 shows a perspective view of the outer connecting
element connecting two stabilization elements.
[0024] FIG. 13 shows an enlarged perspective view of the
stabilization system with two different stabilization elements and
two bone anchors
[0025] FIG. 14 shows a side view of a further connection
element.
[0026] FIG. 15 shows an exploded perspective view of a single
stabilization element together with a polyaxial bone screw.
[0027] FIG. 16 shows the system of FIG. 15 in an assembled and
fixed state.
[0028] FIG. 17 shows an exploded perspective view of the
stabilization system with two different stabilization elements and
a bone anchor.
[0029] FIG. 18 shows a partially sectional view of the system of
FIG. 17 in an assembled and fixed state.
[0030] FIG. 19 shows an exploded perspective view of the
stabilization system with two stabilization elements and a modified
bone anchor.
[0031] FIG. 20 shows a partially sectional view of the system of
FIG. 19 in an assembled and fixed state.
[0032] FIGS. 21a to 21b show a modification of a stabilization
element in a side view and a sectional view along line A-A.
[0033] FIGS. 22a to 22b show a further modification of a
stabilization element in a side view and in a sectional view along
line B-B.
[0034] FIGS. 23a to 23b show a still further modification of the
stabilization element connected to another stabilization element in
a side view and in a sectional view along line C-C.
DETAILED DESCRIPTION
[0035] A modular stabilization system according to the disclosure
is schematically shown in FIG. 1. The system includes at least two,
usually a plurality of rod-like stabilization elements, which may
have the same or different properties and/or geometries. For
example, the modular stabilization system 1 includes flexible
stabilization elements 2, 2', which can be connected by an inner
connection element 3, and an outer connection element 4a, 4b. In
addition, the modular stabilization system may include a rigid
stabilization element 5 which can be connected to a flexible
stabilization element 2, 2' by an outer connection element 4a, 4b.
The term flexible means that the stabilization element, when
implanted in the patient's body, allows a certain degree of flexion
and/or extension and/or torsion of the spinal motion segment. The
term rigid means that it doesn't allow such a limited motion under
normal load conditions of the spinal column. The modular
stabilization system 1 can include further rod-like stabilization
elements 6, 7, which may differ in length and shape compared to the
other stabilization elements. For example, the stabilization
elements 6 differ in cross-section from the stabilization elements
2 and 5. The stabilization element 7, in addition, is curved. Each
stabilization element is connected to a neighbouring stabilization
element via an outer connection element 4a, 4b.
[0036] The term rod-like means that the stabilization element has
elongate shape and can be received in a receiving part of a bone
anchor.
[0037] The stabilization system 1 is connected to bone anchors 8
which are to be anchored in vertebrae of the spinal column. As
shown with respect to the stabilization element 5, the bone anchor
8 may be a pedicle screw having a receiving part to receive the
rod-like stabilization element 5.
[0038] As can be seen in FIGS. 2 and 3, the flexible stabilization
element 2 has a rod-like shape with a first end 2a and a second end
2b and a circular cross-section. At each end a blind hole 21 is
provided extending to a distance from the first end 2a and the
second end 2b, respectively. The blind hole 21 has a portion 22
forming a circular undercut. The outer diameter of the flexible
stabilization element 2 varies over the length of the stabilization
element in such a way that at a distance from the first end 2a and
the second end 2b corresponding to the position of the undercut 22
a circular rib-like projection 23 is formed. The diameter of the
stabilization element 2 further varies in such a way that it
decreases slightly towards the middle of the stabilization element
in a lengthwise direction.
[0039] The flexible stabilization element 2 is made of a material
which is flexible under the application of forces arising from the
motion of the vertebrae against each other. For example, the
material can be an elastomer material, such as polycarbonate
urethane (PCU) or polyurethane or polysiloxane. However, any other
body compatible materials exhibiting flexibility can be used. The
length of the flexible stabilization element is such that usually
one motion segment of the spine can be bridged by the flexible
stabilization element. Hence, the stabilization system may comprise
a plurality of flexible stabilization elements 2 of different
length to apply it to different locations of the spine. Also, the
diameters of such flexible stabilization elements may vary to
provide the desired characteristic for stabilization. The end
portions having the rib-like projections should have the same size
in order to allow the flexible stabilization elements to be
connected to a neighbouring stabilization element via the outer
connection elements described hereinafter.
[0040] FIGS. 4-6 show the inner connection element 3, which is
adapted to connect two of the flexible stabilization elements 2.
The inner connection element is made of a rigid material, such as
metal, in particular a body-compatible metal such as titanium,
stainless steel or body-compatible alloys or of a rigid plastic
material, such as PEEK or others. The shape of the inner connection
element 3 is approximately bar-bell-shaped. In particular, it has
at a distance of each end a circular rib-like projection 33 which
is shaped so as to fit into the undercut portion 22 of the blind
hole 21 of the flexible stabilization element 2 as shown, for
example, in FIG. 10. Hence, the inner connection element 3 can be
inserted in the blind hole 21 of one flexible stabilization element
2 by pressing or snapping it into the bore which is possible due to
the flexibility of the flexible stabilization element 2. For
connection to the second flexible stabilization element 2' it can
be pressed into the blind hole 21 of the second flexible
stabilization element.
[0041] Connected in this way, the stabilization system includes two
flexible stabilization elements 2, which are adapted to bridge two
motion segments of the spine. The connection is established with a
form-fit (also called positive fit) connection between the inner
connection element 3 and the undercut portion 22 of the blind hole
21 of the flexible stabilization element 2.
[0042] The outer connection element according to FIGS. 7-9 includes
two identical halves 4a, 4b which are approximately rectangular in
shape with two long sidewalls 41 and two short side walls 42
connecting the long side walls. The short side walls 42 are
outwardly curved. The curvature serves for allowing the outer
connection element to be introduced in a receiving portion of a
bone anchor and to be moved therein. Each of the outer connection
elements 4a, 4b includes a cylinder segment-shaped recess 43 with
two circular grooves 44 the size and shape of which is designed so
as to fit on the circular rib-like projections 23 of the flexible
stabilization element 2. When the flexible stabilization element 2
is connected to another flexible stabilization element 2' via the
inner connection element 3, the outer connection element 4a, 4b
engages the connection site in a form-fit manner.
[0043] The two halves 4a, 4b of the outer connection element may be
connected outside the receiving portion of a bone anchor. As shown
in FIGS. 10 to 12 an elastic clamp 40 can be used for connecting
the two halves 4a, 4b. To accomplish such a connection, the
portions 4a,4b of the outer connecting element have on their faces
which are opposite to the stabilization elements, grooves 410 which
may have an undercut portion 420 in which a catch portion 430 of
the clamp 40 engages. The clamp 40 can be easily snapped onto the
outer connection element which encompasses the stabilization
elements. The outer connection element thereby firmly connects the
stabilization elements pressure and form-fit connection. Other way
for connecting the two portions of the outer connecting element are
conceivable, such as screw connections, other kinds of snap fit
connections or any other methods and devices.
[0044] The function of the connection between the stabilizing
elements and the outer and inner connecting element is as follows.
The inner connection element 3 connects the two stabilization
elements with a form-fit connection. Thereby, a holding force is
established which provides a preliminary fixation. The outer
connection element 4a, 4b provides an additional holding force with
a form-fit connection since the rib-like projections of the
stabilization element engage in the grooves of the connection
element. In the receiving portion of the bone anchor pressure is
exerted (shown by the arrows in FIG. 1) which presses the halves
4a, 4b against the stabilization elements. Hence, the final
connection is established by a combination of form fit and
frictional fit. The inner connection element 3 prevents a
deformation of the flexible stabilization element. As a
consequence, the holding force is increased.
[0045] FIGS. 13 and 14 show a connection of the stabilization
system to the bone anchor 8. The bone anchor 8 includes a threaded
shaft and a receiving portion 9. The receiving portion 9 is
substantially cylindrically-shaped and includes a coaxial bore 10
with an internal thread 11 at the open end and a substantially
U-shaped recess 12 for receiving the stabilization element. As
shown particularly in FIG. 13, the outer connection element 4a, 4b
is designed such as to be insertable from the open end into the
receiving portion 9 and to be moved therein in an axial direction.
An inner screw 13 is provided to be screwed in into the receiving
portion and to exert pressure on the upper half 4b of the outer
connection element. The pressure exerted by the inner screw presses
the upper half 4b of the outer connection element against the lower
half 4a and the bottom of the U-shaped recess 12, thereby
establishing the form-fit connection of the stabilization elements
and a frictional holding force.
[0046] As further shown in FIG. 13, the stabilization element 5 has
a length with which spans at least one full motion segment. The
stabilization element 5 is a rigid stabilization element which can
be curved, as shown, and which is anchored in a vertebrae in a
usual manner via the bone anchor 8 with receiving portion 9 into
which the middle portion of the stabilization element 5 is directly
inserted and fixed by tightening the inner screw 13.
[0047] The bone anchor 8 shown in FIG. 13 is of the type of a
mono-axial bone anchor which means that the receiving portion and a
threaded shaft are not pivotably connected to each other.
[0048] In the embodiment shown in FIG. 13 the rigid stabilization
element 5 has a circular cross-section and is provided at both ends
with a connection element 14 shown in FIG. 14. The connection
element 14 is rotationally symmetric and comprises a first end 14a
and a second end 14b. Adjacent to the first end 14a a circular
rib-like projection 15 is provided which is shaped like the
rib-like projection 33 of the inner connection element such that,
as shown in FIG. 1, the rigid stabilization element 5 can be
connected to a flexible stabilization element 2. Adjacent to the
second end 14b, the connection element 14 includes a rib-like
projection 16, the outer diameter and the shape of which
corresponds to the outer diameter and the shape of the rib-like
projection 23 of the flexible stabilization element 2 and fits to
the inner structure of the outer connection element 4a, 4b. The
connection element 14 further comprises on its second end 14b a
coaxial blind hole (not shown) for inserting a stabilization
element 6 as shown in FIG. 13. The connection element 14 is of the
flexible type, i.e. it is made, for example, of a flexible material
such as an elastomer, in particular from PCU.
[0049] The stabilization element 6 is rigid and has a non-circular
cross-section, for example a rectangular cross-section. It may have
a projection at its ends to be received in a form fit manner in the
connection element 14.
[0050] FIGS. 15 and 16 show a variation of the bone anchor, which
is in the form of a polyaxial bone screw. It comprises a screw
element 8' which is pivotably held in the receiving portion 9'. To
fix the angular position of the screw element 8', a pressure
element 20 is provided which presses onto the head 8a of the bone
anchor 8'. All other parts with the same reference numerals are the
same as described already in connection with FIG. 13. The
stabilization element 5 shown in FIGS. 15 and 16 is a rigid
stabilization element which is anchored by the polyaxial bone screw
at its middle portion. This is useful if the stabilization element
is intended to cover more than one single motion segment. In such a
case conventional polyaxial bone anchors can be used.
[0051] The stabilization system shown in FIGS. 17 and 18 differs
from the stabilization system shown in FIGS. 15 and 16 in that the
bone anchor is a specifically adapted polyaxial bone anchor to
anchor flexible stabilization elements 2, 2'. The screw element 8'
is the same as the screw element 8' shown in FIGS. 15 and 16. The
receiving part 9'' is also pivotably connected to the screw element
and comprises a central bore 10 which tapers at one end to
pivotably hold the head 8a of the screw element 8'. Also, like in
the embodiment of FIGS. 15 and 16, the U-shaped recess 12 is
provided in the receiving part 9'' and an internal thread 11 for
screwing-in the inner screw 13. The receiving part 9' has a height
which is designed in such a way that an outer connection element
400a, 400b which encompasses the two flexible stabilization
elements 2, 2' and the inner connection element 3 can be
accommodated therein. The flexible stabilization elements 2, 2' are
the same as those shown in FIGS. 2 to 6.
[0052] The outer connection element consists of two halves 400a,
400b which have a generally cylindrical shape and a
cylinder-segment shaped recess 401 to accommodate the end portions
of the flexible stabilization elements between them. Similar to the
outer connection element 4a, 4b shown in FIGS. 7 to 9 the outer
connection element 400a, 400b includes circular grooves 404 to
establish a form-fit connection with the circular ribs 23 of the
stabilization elements 2, 2'. The lower half 400a of the outer
connection element includes a central bore 405 which allows to
access the head 8a of the screw element with a tool. In addition,
the lower half of the outer connection element 400a includes
opposite to the cylinder segment-shaped recess 401, a substantially
spherical recess (not shown) which is adapted to fit onto the head
8a of the screw element 8'. Hence, the function of the lower half
400a of the outer connection element is also the function the
pressure element 20 shown in FIG. 15 which exerts pressure onto the
head of the screw element to lock the head of the screw element in
its angular position. The upper half 400b of the outer connection
element has a flat surface 406, for example.
[0053] As shown in the assembled state according to FIG. 18, when
the inner screw 13 is tightened down, it presses the upper half
400b against the lower half 400a and engages the ends of the
flexible elements 2, 2' in a form-fit connection. When the inner
screw 13 is finally tightened, the angular position of the screw
element with respect to the receiving part and also the connection
between the two flexible elements is fixed.
[0054] The stabilization system shown in FIGS. 19 and 20 differs
from the stabilization system shown in FIGS. 17 and 18 in that the
outer connection element 500a, 500b is partly integrated in the
receiving portion 90. Also, the inner connection element 3' is
adapted to correspond to the outer connection element. As in the
previous embodiment the receiving portion 90 is pivotably connected
to the screw member 8'. The receiving portion 90 has at both sides
of the channel formed by the U-shaped recess 12 a cylinder
segment-shaped projection 500a which forms the lower half of the
outer connection element. The cylinder segment shaped projection
500a includes as in the previous embodiments circular grooves 504
for the purpose of form-fit connection with the circular rib 23 of
the flexible stabilization element 2, 2'. All other portions of the
receiving portion 90 are identical to those of the receiving
portion 9' of the previous embodiment.
[0055] The upper half 500b of the outer connection element is
generally cylindrically-shaped with the cylinder axis being
parallel to the cylinder axis of the channel formed by the U-shaped
recess 12. The upper half 500b comprises a main portion 501 which
presses onto the inner connection element 3' and two cylinder
segment shaped end portions at both ends which are complementary to
the portions 500a at the receiving portion 90 and which have a
circular groove 504 adapted to accommodate the circular rib 23 of
the flexible stabilization element. The length of the central
portion 501 is such that when the upper half 500b is inserted into
the receiving portion 90 the end portions 502 extend beyond the
U-shaped recess and are located so as to face the portions 500a of
the receiving portion. The inner connection element 3' has a
prolonged middle portion the length of which is such that the end
portions extend beyond the receiving portion 90. In addition, a
pressure element 20 which is the conventional pressure element
shown in FIG. 15 is provided to lock the position of the screw head
8a.
[0056] As shown in FIG. 20 the flexible elements 2, 2' are clamped
between the portions 500a and the upper half 500b of the outer
connection element. The clamping takes place outside the central
portion of the receiving portion 90. In the bore 10 of the
receiving portion 90 the rigid inner connection element 3' is
clamped. With this design, the flexible stabilization elements can
be made shorter than in the previous embodiments. It should be
noted that the lower half 500a of the outer connection element
needs not to be integrally shaped with the receiving portion 90 it
is also conceivable that the pressure element 20 comprises
extensions extending beyond the receiving portion.
[0057] FIGS. 21 to 23 show modifications of the flexible
stabilization element. FIGS. 21a and 21b show a flexible
stabilization element 2'' which is curved and which has an
approximately rectangular cross section. This provides an oriented
flexibility, i.e. the element has a higher stiffness in one
direction than in another direction. Generally, in the portion
between the two ends of the stabilization element the cross-section
of the element can be designed such that the desired stiffness or
an oriented flexibility is achieved.
[0058] FIGS. 22a and 22b show a further modification of the
flexible stabilization element 20' which differs in that instead of
a single rib-like circular projection a plurality of fine circular
ribs 20a' are provided which permit balancing of the length of the
stabilization element within the outer connection element 4a,
4b.
[0059] FIGS. 23a and 23b show a further modification of the
flexible stabilization element 200,200' which differs from the
previously described flexible stabilization elements in that a
spherical segment-shaped projection 200a the diameter of which
increases towards the end is provided. This allows a simple
construction of the outer connection element and a free rotational
alignment thereof.
[0060] Other modifications are conceivable. The end portions of the
stabilization elements need not have a circular rib-like
projection. Any structure, which can provide a form-fit connection,
is suitable. The rigid stabilization elements can be shaped at the
ends to be insertable in the blind hole of the flexible
stabilization element. The inner connection element may be
omitted.
[0061] The outer connection elements have to be adapted to the
shape of the end portions of the flexible stabilization elements. A
particular modification can be that the outer connection elements
4a, 4b are not provided as separate elements but integrated into
the bone anchors. In this case, either the bottom of the U-shaped
recess and/or the lower portion of the fixation screw 13 has a
structure for form-fit engagement. Alternatively, only the upper or
the lower structure is integrated into the receiving portion and
the complementary other structure is provided in a separate
element. Providing the outer connection element as a separate
element, has the advantage that existing bone anchors can be used
and upgraded with the outer connection element.
[0062] Any known bone anchors can be used. The fixation is not
restricted to an inner screw as a fixation element.
[0063] In operation, the surgeon anchors at least two, usually a
plurality of bone anchors in adjacent vertebrae of the portion of
the spine which is to be stabilized. Thereafter, the stabilization
system is assembled by selecting appropriate flexible and/or rigid
stabilization elements and connecting them outside the patient's
body. Then the assembled rod-like stabilization system is inserted
in such a way that it is fixed in the bone anchors at the
connection sites. Finally, the inner screws are tightened to fix
the system in the bone anchors.
* * * * *