U.S. patent application number 10/348322 was filed with the patent office on 2004-04-15 for intervertebral prosthesis.
This patent application is currently assigned to Link Spine Group, Inc.. Invention is credited to Keller, Arnold.
Application Number | 20040073307 10/348322 |
Document ID | / |
Family ID | 32038619 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040073307 |
Kind Code |
A1 |
Keller, Arnold |
April 15, 2004 |
Intervertebral prosthesis
Abstract
Intervertebral prosthesis (10) with at least one cover plate
(11) which bears on a vertebral body (1) and is to be firmly
connected thereto. In order to ensure that the prosthesis (10),
during its insertion or during its lifetime, does not contribute to
a protruding bone margin (5) breaking off, the cover plate (11) is
provided with a bulge (12) corresponding to the depression (4)
and/or with a bevel, a shortened end or rounded end (13).
Inventors: |
Keller, Arnold; (Kayhude,
DE) |
Correspondence
Address: |
Barry E. Bretschneider
Morrison & Foerster LLP
Suite 300
1650 Tysons Boulevard
McLean
VA
22102
US
|
Assignee: |
Link Spine Group, Inc.
Branford
CT
|
Family ID: |
32038619 |
Appl. No.: |
10/348322 |
Filed: |
January 22, 2003 |
Current U.S.
Class: |
623/17.11 |
Current CPC
Class: |
A61F 2002/3065 20130101;
A61F 2220/0041 20130101; A61F 2002/443 20130101; A61F 2002/30649
20130101; A61F 2002/30736 20130101; A61F 2230/0069 20130101; A61F
2002/30387 20130101; A61F 2002/30578 20130101; A61F 2/30767
20130101; A61F 2002/30841 20130101; A61F 2/442 20130101; A61F
2002/30433 20130101; A61F 2/4425 20130101; A61F 2002/3023 20130101;
A61F 2220/0025 20130101; A61F 2002/30616 20130101 |
Class at
Publication: |
623/017.11 |
International
Class: |
A61F 002/44 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 14, 2002 |
DE |
102 47 762.0 |
Claims
1. Intervertebral prosthesis with at least one cover plate (11, 19)
which bears on a vertebral body (1, 2) and is to be connected
thereto, characterized in that the cover plate surface directed
toward the vertebral body (1) has a bulge (12) protruding beyond
the level of adaptation to the normal shape of the vertebral
body.
2. Intervertebral prosthesis according to claim 1, characterized in
that the bulge (12) has a smaller extent than the cover plate
surface.
3. Intervertebral prosthesis according to claim 2, characterized in
that the bulge (12) lies nearer to the dorsal margin (13) of the
cover plate surface than to its ventral margin.
4. Intervertebral prosthesis according to claim 3, characterized in
that the bulge (12) reaches as far as the dorsal edge (13) of the
cover plate surface.
5. Intervertebral prosthesis in particular according to claim 4,
with at least one cover plate (11, 14) which bears on a vertebral
body (1) and is to be connected thereto, characterized in that a
bevel or rounding (13, 16) is provided at the margin of the cover
plate surface directed toward the vertebral body (1).
6. Intervertebral prosthesis according to claim 5, characterized in
that the bevel or rounding (13, 16) is provided at least on the
dorsal side.
7. Intervertebral prosthesis according to claim 5 or 6,
characterized in that the bevel or rounding (13, 16) extends over
at least 5% of the dimension of the cover plate surface in the A-P
direction.
8. Intervertebral prosthesis according to one of claims 5 to 7,
characterized in that the bevel or rounding (13) is part of a bulge
(12) according to claim 4.
9. Intervertebral prosthesis in particular according to one of
claims 1 to 8, with at least one cover plate (14) which bears on a
vertebral body (1) and is to be connected thereto and which has
teeth (17) intended to penetrate into the vertebral body (1),
characterized in that the distance of the teeth (17) from the
dorsal edge of the cover plate (14) is at least 20% of the cover
plate size in the A-P direction.
10. Intervertebral prosthesis according to claim 9, characterized
in that at least one of the teeth (17) arranged near the dorsal
edge and designed to be self-cutting extends substantially in a
sagittal direction.
11. Intervertebral prosthesis according to claim 9, characterized
in that at least one of the teeth arranged near the dorsal edge has
a lower height than teeth arranged further in the ventral
direction.
12. Intervertebral prosthesis according to one of claims 1 to 11,
characterized in that the bulge (12) or bevel or rounding (13, 16)
is formed by a separate attachment part (20) connected, or to be
connected, to the cover plate (19).
13. Intervertebral prosthesis according to claim 12, characterized
in that a plurality of different attachment parts (20) are
provided, and a small number of different cover plates (19) which
can be connected to them.
14. Set of intervertebral prostheses which comprise at least one
cover plate (11, 19), with a substantially flat cover plate
surface, which bears on a vertebral body (1) and is to be connected
thereto, characterized in that it comprises at least one
intervertebral prosthesis whose cover plate surface has a bulge
(20).
15. Set of intervertebral prostheses which comprise at least one
cover plate (11, 19) which has a dorsal margin and which bears on a
vertebral body (1) and is to be connected thereto, characterized in
that it comprises at least one intervertebral prosthesis on whose
cover plate the dorsal margin is shortened.
Description
[0001] The cover plates of the vertebral bodies between which the
intervertebral disks of the spinal column are situated are
generally flat or slightly concave. A pronounced concavity of the
cover plates sometimes occurs, particularly in the lower region of
the spinal column. Although this is not necessarily caused by
injury, it can be. For example, it can sometimes happen that, after
an intervertebral disk prolapse, the margin of a vertebral body
impinges on the cover plate of the adjacent vertebral body and
grinds out a depression there. Regardless of how the pronounced
concavity has arisen, it leads to inadequate support of the dorsal
margin, from which osteophytes may also project in some cases. If a
prosthesis is now introduced into the intervertebral space, it can
easily happen that the dorsal edge of the prosthesis impacts
against the inadequately supported margin of the vertebral body or
against osteophytes and thus breaks off part of the bone in the
direction of the medullary canal, where it poses a danger to the
spinal cord. The same thing can also happen if the prosthesis is
implanted and, because of its insufficient support in the area of
the depression, places too great a load on the margin of the
vertebral body.
[0002] Even in normally structured vertebral bodies, it can happen
that, when an intervertebral prosthesis is inserted, the margin of
the cover plate of the vertebral body is subjected to such stresses
by the edge of the intervertebral prosthesis that it is
damaged.
[0003] It is the object of the invention to ensure that in such
cases parts of the vertebral body cannot break off. To solve this
problem for the first time, the invention provides various
possibilities, namely those set forth in claims 1, 5, 8, 13, 14 and
15 and in their dependent claims.
[0004] The first solution lies in the fact that, on its cover plate
surface directed toward the vertebral body, the intervertebral
prosthesis has a bulge which positions itself in a depression in
the bone of the vertebral body in order on the one hand to obtain
an improved support for the prosthesis there and on the other hand
to protect the projecting bone margin next to the depression. This
bulge rises above the usually flat basic shape, or, in adaptation
to the natural shape of the vertebral, at the very most sligtly
concave basic shape, of the cover plate surface. The bulge is
compared to the flat or only slightly concave shape of the cover
plates of the vertebral bodies or compared to prosthetic cover
plates intended for normal cases of use.
[0005] If the pronounced concavity or depression affects only part
of the bone surface, then, accordingly, the bulge also
advantageously has a smaller extent than the cover plate surface in
the A-P and/or L-M direction. It preferably lies nearer to the
dorsal margin of the cover plate surface than to its ventral
margin. It goes without saying that, in terms of its height, extent
and position, the bulge should be approximated as far as possible
to the shape of the vertebra found. In this respect, it generally
proves expedient if the bulge reaches as far as the dorsal edge of
the cover plate surface.
[0006] The bulge should be approximated as far as possible to the
shape of the depression which is to receive it. For this purpose,
simple geometric shapes often suffice, for example those of a
portion of a cylinder with a transversely lying axial direction, a
portion of a sphere, or a portion of an ellipsoid.
[0007] According to a related solution of the invention, the margin
of the cover plate surface directed toward the vertebral body is
beveled or rounded. This ensures that, when the prosthesis is being
inserted, the prosthesis margin does not come up sharp and hard
against the dorsal bone margin, but instead slides along the
latter. In addition, the bone margin is relieved of force
transmission, which is taken over by other areas better able to
provide support. This embodiment of the prosthesis is used in
particular if the depression is not great and/or can be filled with
bone cement. This embodiment can also be expedient if the vertebral
body is normally structured and only the danger of excessive
loading of the margin of the vertebral body by a prosthesis edge is
to be avoided. This embodiment can also be combined with the
aforementioned bulge. The bulge then forms the bevel or rounding or
merges into these. The bevel or rounding is especially of interest
on the dorsal side, but it can also be of advantage on the other
sides of the prosthesis.
[0008] The invention has further recognized that the teeth or
projections which are provided on the cover plate of the
prosthesis, in order to penetrate into the bone and anchor
themselves there, can contribute to damaging the weakened dorsal
margin of the vertebral body. They should therefore maintain a
distance, from the dorsal edge of the cover plate, of at least 20%,
preferably more than 30%, of the greatest dimension of the cover
plate measured in the A-P direction. If the teeth are of a
self-cutting and planar design, i.e. in the form of small plates
whose main plane is transverse with respect to the bone surface, it
can also be expedient for their main plane to extend in the
sagittal direction. This applies in particular to those teeth which
are arranged near the dorsal margin of the cover plate. This
ensures that, upon insertion of the prostheses into the
intervertebral space, these teeth subject the bone to only slight
dorsally directed forces and thus protect the possibly weakened
areas of the bone. Finally, it can be expedient for the teeth near
the dorsal margin to be made smaller than the teeth arranged
further in the ventral direction, for example half the height of
the latter. In some cases it may suffice to limit this measure to
one or just a few of the dorsal teeth, for example to the middle
tooth within a group of three dorsal teeth, which tooth, if
appropriate, can also be omitted so that there are only two dorsal
anchoring teeth.
[0009] As long as the injuries are typical ones often occuring in
the same form, standardized cover plates with different sizes or
shapes of the bulge, bevel or rounding can be provided. However, as
it will often be necessary to take account of the particular shape
and position of the bone depressions, it is preferable, according
to the invention, to design at least the bulge, but if appropriate
also the bevel or rounding, as a separate attachment part which can
be connected to a suitable cover plate. It is then possible to
provide quite a large number of different attachment parts. Of
these, the one suitable for the specific case can be selected and
connected to the cover plate, if appropriate also in a different
chosen position. A collection of vertebral prostheses according to
the invention can therefore provide a large number of different
attachment parts and at least one cover plate, but preferably
several different cover plates, connectable to these attachment
parts. It may also suffice to have one cover plate which permits
various possible arrangements of the attachment parts.
[0010] A set of intervertebral prostheses according to the
invention is characterized in that it comprises at least one
intervertebral prosthesis whose cover plate surface has a bulge
protruding farther than the cover plate surface in the other,
normal prostheses.
[0011] The invention is explained in more detail below with
reference to the drawing which depicts advantageous illustrative
embodiments. In the drawing:
[0012] FIG. 1 shows a sagittal section through a portion of the
spinal column,
[0013] FIG. 2 shows the conditions upon insertion of a conventional
prosthesis between a pair of vertebral bodies,
[0014] FIGS. 3-5 show the corresponding configuration with
prostheses formed according to the invention,
[0015] FIG. 6 shows the plan view of a cover plate surface and its
arrangement of teeth, and
[0016] FIG. 7 shows the side view of a cover plate with modular
bulge attachment.
[0017] The pair of vertebral bodies 1, 2 enclose an intervertebral
disk 3 between their mutually facing cover plates. Near its dorsal
margin, the upper vertebral body 1 has a depression 4 in the
surface of its lower cover plate. This depression can be a
phenomenon resulting from degeneration or it can be a natural
formation. Behind the depression 4, a bone margin 5 remains which,
because of the absence of bone substance on its side toward the
depression, is not well supported and is therefore susceptible to
fracturing.
[0018] If, in accordance with FIG. 2, a conventional intervertebral
prosthesis 6 is inserted into the space between the spread-apart
vertebral bodies 1 and 2 in the arrow direction, it can happen that
the sharp dorsal edge 7 of the prosthetic cover plate strikes
against the sensitive bone margin 5 and completely or partially
breaks the latter off in the dorsal direction.
[0019] This happens less readily in the first embodiment of a
prosthesis according to the invention shown in FIG. 3. Near its
dorsal margin, the cover plate 11 is provided with a bulge 12 which
has been selected so that it corresponds approximately to the shape
of the depression 4. Its surface can be approximated to the shape
of a portion of a cylinder, with an axis lying preferably in the
lateral-medial direction, or of a sphere or of an ellipsoid. In
contrast to the conventional illustrative embodiment in FIG. 2, its
dorsal margin 13 is not designed with a sharp edge, but is instead
beveled or rounded. The bevel or rounding merges monotonously (i.e.
without any substantial change of direction) into the surface of
the bulge 12. Even if the prosthesis, during insertion, were to be
upwardly directed obliquely rearward toward the vertebral body 1 so
that the cover plate 11 slides along the surface of the vertebral
body, there is no danger of the leading, dorsal margin 13 of the
cover plate 11 coming up hard against the bone margin 5. It will
instead slide gently along the latter without exerting any
dangerous force on it. Likewise, in the inserted state, the bevel
or rounding 13 ensures that no excessive forces are transmitted in
the area of the bone margin 5. Instead, the cover plate 11 is
supported, by virtue of its bulge 12, in the depth of the
depression 4.
[0020] FIG. 4 shows an example in which the cover plate 14 of the
prosthesis 15 does not have a bulge, but instead only a bevel 16 at
its dorsal margin. During insertion, the bevel ensures that the
rear edge of the cover plate 14 slides gently along the bone margin
5, if it touches the latter at all. FIG. 5 shows that, in the
inserted state, the bevel 16 avoids direct contact between the
cover plate 14 and the bone margin 5 and thus rules out any danger
to the latter. Instead of this, the cover plate, whose normal
dorsal limit is indicated in FIG. 6 by the line 24, can also be
shortened or straightened dorsally, as is shown by the line 25.
This embodiment of the invention is comparable to those prostheses
of the same order of size which are provided for normal cases of
use. It may be necessary to provide smaller prosthesis cores for
the cover plates shortened at the dorsal end.
[0021] FIGS. 4 and 5 show that the cover plates of the prosthesis
15 are provided with teeth 17, 18 which have the shape of small
triangular plates, their plane being perpendicular to the plane of
the cover plate. They are made so sharp that they automatically
sink into the bone surface when the spreading-apart of the
vertebral bodies is reversed after insertion of the prosthesis. It
is known to arrange such teeth parallel to the margin
(EP-A-1057462). For the teeth 18 arranged along the ventral margin
of the cover plate 14, this is also the case in the present
illustrative embodiment. However, the teeth 17 arranged nearer the
dorsal margin 16 are, on the one hand, at a considerable distance
from this margin and, on the other hand, are aligned in the A-P
direction, with the result that, during insertion into a narrow
intervertebral space or during sinking into the bone surface or,
later, during normal functioning of the prosthesis, said teeth
cannot apply a damaging, dorsally directed force on the bone.
Moreover, their height can be made smaller than that of the teeth
18. These measures can be employed jointly or independently of one
another.
[0022] FIG. 7 illustrates the possibility of providing a cover
plate 19 with differently shaped bulges 20. For this purpose,
interacting securing means are provided which, in the simplest
case, can consist of screws or pins. In the example shown, they
comprise tenons and mortises 21 in the manner of a dovetail
joint.
[0023] The prosthetic cover plates are provided for a secure
connection to the cover plates of the vertebral bodies. Suitable
connecting means can be provided for this purpose. For example, the
cover plates 6, 11, 14 are equipped with ventral flanges 22 which
in a known manner can be used for screwing to the bone and which
safeguard against inserting the prosthesis too far into the
intervertebral space. Another example of anchoring the prosthesis
to the bone is a biological coating which promotes bone growth and
interconnection.
[0024] An explanation of the prosthesis core has not been given
here, because this prosthesis core is known in a wide variety of
forms, which can also be used in conjunction with the
invention.
[0025] What is to be considered as a bulged cover plate and what is
to be considered as a normal cover plate surface must be determined
by comprison between the normal prostheses and the bulged
prostheses of one and the same set of prostheses. The cover plate
surfaces which are intended to bear on the vertebral body are in
most cases basically flat. In some cases, the normal cover plate
surface has a slight convex curve which complements the average
curvature of the vertebral body surfaces. The bulge is then the
convex area which rises above a correspondingly naturally flat or
slightly curved imaginary surface of the cover plate. A bulge
according to the invention is at any rate to be regarded as a part
of the prosthetic cover plate whose radius of curvature in the
sagittal plane is less than 40 mm, preferably 30 mm, or which rises
above the arc 26 (see FIG. 7) which in the sagittal plane extends
through the edges of the cover plate and has an arc height of 4 mm,
preferably 3 mm, over the straight connection line of these
edges.
* * * * *