U.S. patent application number 11/137707 was filed with the patent office on 2006-03-23 for prosthesis for bridging a vertebral body.
This patent application is currently assigned to Cervitech, Inc.. Invention is credited to Arnold Keller.
Application Number | 20060064168 11/137707 |
Document ID | / |
Family ID | 34926678 |
Filed Date | 2006-03-23 |
United States Patent
Application |
20060064168 |
Kind Code |
A1 |
Keller; Arnold |
March 23, 2006 |
Prosthesis for bridging a vertebral body
Abstract
Prosthesis for the partial replacement of a vertebral body, with
an upper contact plate (5) for connection to an upper vertebral
body (1), a lower contact plate (6) for connection to a lower
vertebral body (2), and a bridging part (7) which connects the
upper and lower contact plates (5, 6) to one another and bridges at
least one vertebral body (3) which is located between the upper and
lower vertebral bodies (1, 2) and is to be partially replaced. The
bridging part (7) is accommodated in a recess in the vertebral body
(3). To be secured in said recess, it has lateral anchoring
projections (9) which penetrate into the bone substance located on
both sides of the bridging part (7). Its cross section narrows
toward the rear preferably in a trapezoid shape.
Inventors: |
Keller; Arnold; (Kayhude,
DE) |
Correspondence
Address: |
Barry E. Bretschneider;Morrison & Foerster LLP
Suite 300
1650 Tysons Boulevard
McLean
VA
22102
US
|
Assignee: |
Cervitech, Inc.
Rockaway
NJ
|
Family ID: |
34926678 |
Appl. No.: |
11/137707 |
Filed: |
May 26, 2005 |
Current U.S.
Class: |
623/17.11 ;
623/17.15 |
Current CPC
Class: |
A61F 2002/30841
20130101; A61F 2/44 20130101; A61F 2002/30784 20130101; A61F
2002/30663 20130101; A61F 2002/30565 20130101; A61F 2002/30576
20130101 |
Class at
Publication: |
623/017.11 ;
623/017.15 |
International
Class: |
A61F 2/44 20060101
A61F002/44 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 23, 2004 |
EP |
04022671.4 |
Claims
1. Prosthesis for partial replacement of a vertebral body, with an
upper contact plate (5) for connection to an upper vertebral body
(1), a lower contact plate (6) for connection to a lower vertebral
body (2), and a bridging part (7) which connects the upper and
lower contact plates (5, 6) to one another, with inclusion of at
least one hinge (8), and is designed for bridging at least one
vertebral body (3) which is located between the upper and lower
vertebral bodies (1, 2) and is to be partially replaced, said
bridging part (7) being equipped with means for securing it on the
vertebral body (3), characterized in that the means for securing it
on the vertebral body (3) are formed by rigid anchoring projections
(9, 11, 15, 32) which protrude laterally from the bridging part
(7).
2. Spinal column prosthesis according to claim 1, characterized in
that the cross-sectional shape of the bridging part (7) is
rectangular or narrows in the dorsal direction.
3. Spinal column prosthesis according to claim 1, characterized in
that the anchoring projections are in the form of a surface
roughness.
4. Spinal column prosthesis according to claim 1, characterized in
that the bridging part (7) has openings (12) or pores for receiving
bone tissue.
5. Spinal column prosthesis according to claim 4, characterized in
that it is provided with a filling of bone material or bone
replacement material.
Description
[0001] The invention relates to a prosthesis according to the
preamble of claim 1. This is based on a known prosthesis
(DE-A-4109941, FIG. 2) which comprises an upper contact plate for
connection to an upper vertebral body, a lower contact plate for
connection to a lower vertebral body, and a bridging part which
connects the upper and lower contact plates and is designed for
bridging at least one vertebral body which is located between the
upper and lower vertebral bodies and whose function is to be
replaced by the prosthesis. Between the bridging body and the
contact plates, a hinge is in each case provided for replacement of
the intervertebral discs. The cross-sectional size of the bridging
part is considerably smaller than that of this vertebral body. If
the latter is more or less completely preserved, the bridging part
should be fitted into it in such a way that it is completely
embedded therein. How this could be done surgically is unclear. If
it is still more or less complete only on the vertebral arch side,
a recess is created on its front face and the bridging part is
inserted into said recess. For firm connection to the vertebral
body, the bridging part has laterally protruding webs which contain
an oblong hole for receiving a securing screw. The securing of the
prosthesis on the vertebral body determines, in addition to the
facet articulations, the position of said vertebral body with
respect to the adjacent vertebral bodies. Only when those surfaces
of the vertebral body intended for the securing webs to bear on are
worked in such a way that the vertebral body, after connection to
the webs, can maintain its natural position defined by the facet
articulations, is there any prospect of the prosthesis fitting in a
way that does not cause discomfort. Such precise working is
difficult to achieve. It has also been found that securing by means
of a screw is not reliable enough.
[0002] In another known spinal column prosthesis (U.S. Pat. No.
5,423,816), the bridging part is formed by a coil spring which,
because of its compliance, has the purpose of permitting a relative
movement of the upper and lower vertebral bodies with respect to
one another and to the bridged vertebral body. The coil spring is
intended to be received in a cavity inside the vertebral body to be
bridged, which is also filled with bone chips which may possibly
permit new growth of bone tissue inside the cavity. However,
because of their constant relative movement, a firm connection
between the turns of the coil spring and the bone tissue is not
possible. Therefore, the turns of the coil spring do not form a
securing means with respect to the bridged vertebral body. On the
contrary, the turns of the coil spring which are being constantly
moved relative to the bridged vertebral body are a cause of
persistent irritation.
[0003] A spinal column prosthesis is also known (EP-A-1417940) in
which the bridging part has a U-shaped configuration in side view,
so as to engage with its branches on the lower face and upper face
of the vertebral body to be replaced. The web lies on the front
face of the vertebral body and is screwed onto it. This requires
suitable working of the vertebral body on its upper, lower and
front faces, which can be difficult, especially if the vertebral
body is damaged. Spinal column prostheses are also known in which
the bridging part completely replaces the vertebral body
(EP-A-567424, WO 0103614, DE-U-20115281, U.S. Pat. No. 5,895,428).
This has the disadvantage that a supporting connection is not
really possible between the remaining parts of the vertebra and the
bridging part.
[0004] In another known group of spinal column prostheses (U.S.
Pat. No. 4,892,545, U.S. Pat. No. 4,636,217), the bridging part is
connected rigidly to the upper and lower vertebral bodies, so that
these too are rigidly connected to one another. The bridged
vertebral body is in this way kept free from forces and therefore
does not require any supporting connection to the bridging part of
the prosthesis.
[0005] The object of the invention is therefore to make available a
spinal column prosthesis of the type mentioned at the outset which
can also be used when the vertebral body to be replaced is
completely or to a large extent preserved. A further aim is that a
comparatively simple operating technique will permit a good
supporting connection between the implant and the vertebral body to
be replaced.
[0006] This is achieved by the features of claim 1. It is
comparatively easy to create a recess in the vertebral body
starting from the front face, which recess matches the shape of the
bridging part and receives the latter substantially in its
entirety. The bridging part is accordingly designed narrower than
the vertebral body. By virtue of the mutual positive engagement
between the bridging part and the recess, the bridging part and the
vertebral body support each other. The bridging part is also unable
to escape from the recess, because its lateral projections hold it
securely in the recess.
[0007] A dowel for rigid connection of adjacent vertebral bodies is
known (U.S.-A-2002/0128652) which has a rectangular cross section
and is fitted into a correspondingly shaped ventral recess in the
vertebral body in question and is equipped with means intended to
prevent its escaping from the recess. However, it is not possible
to tell how these means are designed.
[0008] The mutual supporting action and the securing afforded by
the lateral projections of the bridging part are all the more
effective, the more precisely the recess is adapted to the shape of
the bridging part. This is achieved most easily if the
cross-sectional shape of the recess is rectangular or trapezoid.
This also has the advantage that the side surfaces of the bridging
part are large and thus make it easier to accommodate a plurality
of anchoring projections. This is especially the case when these
are arranged rigidly on the bridging part, for example in the form
of a large number of small points. These are expediently designed
so that, when the bridging part is pressed into the recess, they
find their way to their anchoring position through the elastic or
plastic compliance of the bone tissue. In this connection, the
bridging part shape narrowing in cross section in the dorsal
direction has the further advantage that, as the bridging part is
wedged into the vertebral body recess likewise narrowing in cross
section in the dorsal direction, the projections are sunk into the
bone substance. They can also have a self-cutting design. Another
possible embodiment is one in which the projections are made very
small in the form of a surface roughness. This is generally
sufficient to create an initial strength of the implant/bone
connection and, after a short time, to permit permanent connection
by means of bone tissue growing into the surface roughness. The
projections can be barb-shaped in order to provide minimal
resistance to the movement of the implant into the recess of the
bone, but to provide greater resistance to its removal from the
recess.
[0009] At least on the side surfaces, the bridging part can have
openings or pores for receiving bone tissue. These can be filled
with bone chips before implantation. Over the course of time,
living bone tissue grows in, so as to permit firm union between the
implant and the bones.
[0010] The invention has particular advantages when applied to the
cervical spine.
[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 longitudinal section through an illustrative
embodiment in the median plane,
[0013] FIG. 2 shows a front view of the same implant, and
[0014] FIG. 3 shows a perspective view of the bridging part.
[0015] FIG. 2 shows an upper vertebral body 1 and a lower vertebral
body 2 and, between them, the vertebral body 3 which is to be
replaced. A spinal column prosthesis is inserted between the upper
and lower vertebral bodies. This prosthesis comprises an upper
contact plate 5 connected to the upper vertebral body 1, a lower
contact plate 6 connected to the lower vertebral body 2, and a
bridging part 7 which connects the plates 5 and 6. Located between
the contact plates 5 and 6 and the bridging part 7 there is in each
case a hinge (for example according to EP-A-560140) with a hinge
surface 8. This is formed, in the upper hinge, on the one hand by
the bottom face of the contact plate 5 and on the other hand by a
hinge part 4 connected to the bridging part 7 in a manner not
shown. In the lower hinge, it is formed on the one hand by the
bottom face of the bridging part 7 and on the other hand by the
hinge part 4, which is connected to the lower contact plate 6 in a
manner not shown. Instead of a hinge with a spherical hinge
surface, another hinge type can also be used, for example one with
a flexible cushion (DE-U-20115281) or with a spiral spring
(DE-A-4109941). If the upper vertebral body 1 and the lower
vertebral body 2 are to be rigidly connected, the hinges can also
be omitted altogether. Finally, it is possible to use just one
hinge between the upper contact plate 5 and the bridging part 7, or
between the lower contact plate 6 and the bridging part 7.
[0016] While the contact plates 5 and 6 have a customary size which
is dimensioned in the interest of low pressure forces between the
contact plates and the associated vertebral bodies, the bridging
part 7 has a width which is smaller than that of the associated
vertebral body 3, that is to say small enough to ensure that the
bridging part can be inserted into a recess which has been worked
into the relevant vertebral body 3 from the front face and the bone
substance remaining alongside it suffices for securely anchoring
the bridging part in the recess.
[0017] At least part of the recess has a shape which corresponds as
exactly as possible to the shape of the bridging part 7. It is thus
possible for the surface of the implant to bear on the artificially
created surface of the bone in a manner substantially free from
play. On the one hand, this provides a good mutual support. On the
other hand, it affords the possibility of bone growth creating a
stable connection between the bone and the implant. Finally, this
ensures that the anchoring projections 9 provided on the implant
engage in the bone tissue along substantially their full length in
order to be able to transmit the anchoring forces.
[0018] The object of providing shape correspondence between the
bridging part and the recess created in the bone is achieved most
easily with a trapezoid shape of the cross section of the bridging
part, as is indicated in FIG. 3. It is also possible to use other
cross-sectional shapes, but preferably ones which narrow from the
front toward the rear so that, when the bridging part is inserted
into the recess, the side surfaces bear on the resected bone
surfaces in said manner free from play.
[0019] The feature according to which the bridging part has a
rearwardly narrowing, in particular trapezoid shape ought if
appropriate to merit protection independently of the characterizing
features of claim 1.
[0020] The anchoring projections are arranged rigidly on the side
surfaces 10 of the bridging part 7. According to FIG. 3, they are
in the form of a large number of small, pointed elevations 11 which
force themselves into the bone surface as the implant is inserted
into the recess in the vertebra. In an alternative embodiment not
shown, they are larger and in the form of blades, the plane of the
blades extending in the direction of insertion so that they cut
into the bone substance. Another embodiment uses micro-projections
in the form of a surface roughness that covers the entire side
surface 10 or a substantial part thereof. In each case, in addition
to the anchoring projections, it is possible to provide openings 12
or pores into which bone substance can grow and anchor itself. To
accelerate this process, the openings can be filled from the start
with bone chips. It is also possible to coat the implant with
osteoconductive or osteoinductive substance.
* * * * *