INTERVERTEBRAL DISK PROSTHESIS

PROTHESE DE DISQUE INTERVERTEBRAL

English Abstract

The invention relates to an intervertebral disk prosthesis comprising two
cover plates and a prosthesis core that is joined to one of the cover plates
(1) by means of connecting profiles (8, 8', 14, 14') which are undercut in a
complementary manner. Said connecting profiles (8, 8', 14, 14') are provided
with at least one couple of profiled sections (9, 16) that are symmetric in
relation to the anterior-posterior direction (10) and are disposed at an angle
from each other.

French Abstract

La présente invention concerne une prothèse de disque intervertébral qui comprend deux plaques de couverture et un noyau de prothèse qui est relié à une des plaques de couverture par des profilés de raccord (8, 8 , 14, 14 ) à contre-dépouille complémentaire. Ces profilés de raccord (8, 8 , 14, 14 ) comprennent au moins une paire de sections profilées (9, 16) qui sont placées de manière angulaire l'une par rapport à l'autre et symétrique à la direction AP (10).

Claims

6
claims
1. An intervertebral disk prosthesis with two cover
plates and a prosthesis core (5) which is con-
nected to one of the cover plates (1) by means of
connection profiles (8, 8', 14, 14') which are un-
dercut in a complementary manner, characterized in
that the connection profiles (8, 8', 14, 14') in-
clude at least one pair of profile sections (9,
16) which are symmetrical with respect to the AP
direction (10) and are arranged at an angle to one
another.
2. The intervertebral disk prosthesis as claimed in
claim 1, characterized in that the profile sec-
tions (9, 16) arranged at an angle to one another
run in a substantially straight line.
3. The intervertebral disk prosthesis as claimed in
claim 1 or 2, characterized in that the profile
sections (9, 16) arranged at an angle to one an-
other are arranged on the dorsal side and are held
in engagement by means (11, 18) arranged on the
ventral side.
4. The intervertebral disk prosthesis as claimed in
claim 3, characterized in that the profile sec-
tions (9, 16) arranged on the dorsal side are pro-
vided in addition to a pair of laterally arranged
profile sections (7').
5. The intervertebral disk prosthesis as claimed in
claim 1 or 2, characterized in that the angle (a)
between the profile sections (9, 16) arranged at
an angle to one another is not greater than 150°.

Description

CA 02531144 2006-O1-03
Cervitech, Inc.
CERT026PW0
D/so
Intervertebral disk prosthesis
A known type of intervertebral disk prosthesis (WO
01/01893) has two metal cover plates and a polyethylene
prosthesis core which forms a pair of slide surfaces with
one of the two cover plates and is fixed on the other cover
plate. For this fixing, the cover plate is provided with
edge ridges whose undercut connection profile cooperates
with a complementary connection profile on the underside of
the prosthesis core. On the right and left lateral edges of
the cover plate and of the prosthesis core, such connection
profiles are provided parallel to one another. In addition,
there is one such profile running in a straight line on the
dorsal edge of the cover plate and of the prosthesis core.
There is no such profile on the ventral edge, with the re-
sult that the prosthesis core can be pushed into the con-
nection profiles of the cover plate from the ventral direc-
tion. The prosthesis core is secured in the assembled posi-
tion by a pair of locking elements provided on the ventral
edge. Although the connection profiles are produced almost
free of play, an important concern in prosthesis production
is to ensure that, even in the case of production toler-
ances, it is possible to rule out any movement of the pros-
thesis core relative to the cover plate holding it. In par-
ticular, rotation movements of the prosthesis core relative
to the cover plate holding it must be ruled out.
The prior art gives no indications as to how this problem
could be solved. FR-A-2718635 discloses connection profiles
only on parallel, lateral edges of the cover plate. They
are absent in all the nonlateral and nonparallel edge ar-

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eas. For knee prostheses, FR-A-2632516 discloses the fixing
of a polyethylene part in a retaining profile by means of
horseshoe-shaped connection profiles, but this does not af-
ford any guarantee that the nonparallel sections of the
connection profiles will also remain in engagement with one
another. For a shoulder prosthesis, FR-A-2780635 discloses
the fixing of a polyethylene part on a retaining part by
means of connection profiles extending exclusively at an
angle with respect to one another. This cannot be adapted
the shape requirements of an intervertebral disk prosthe-
sis.
The invention has recognized that the problem with in-
tervertebral disk prostheses can be solved by the special
arrangement of the connection profiles given in claim 1.
Accordingly, provision is made that the connection profiles
include at least one pair of connection profile sections
which are symmetrical with respect to the AP direction and
are arranged at an angle to one another. AP direction sig-
nifies the anteroposterior direction. The profile sections
arranged at an angle to one another according to the inven-
tion create a triangular configuration which counteracts
twisting of the prosthesis core relative to the cover plate
if play exists between the connection profiles of the cover
plate and of the prosthesis core. The connection profiles
can basically be made up exclusively of such profile sec-
tions arranged at an angle to one another. However, these
can also be provided additionally to connection profiles
arranged in parallel on the lateral edges of the cover
plate and of the prosthesis core. They are intended to run
in a substantially straight line and are preferably ar-
ranged at least on the dorsal side. The angle between the
profile sections arranged at an angle to one another should
not be greater than 150°. The limit preferably lies for ex-
ample at 140°.

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The invention is explained in more detail below with refer-
ence to the drawing which depicts an advantageous illustra-
tive embodiment and in which:
Fig. 1 shows a perspective view of the end plate
with the prosthesis core secured on it,
Figs 2 to 4 show different views of the same end plate
without prosthesis core, and
Figs 5 and 6 show perspective views of the prosthesis
core.
The end plate 1, which is normally used as the lower end
plate, has an approximately oval contour and comprises a
toothed fastening surface 2 for bearing on the vertebral
body and a flange 3 which comes to lie on the ventral side
of the vertebral body and can be screwed to the latter via
screw holes 4. On that side opposite the fastening surface
2, the one normally lying to the top, the cover plate 1
forms a support for the prosthesis core 5. This support
consists of a plane surface 6 and, surrounding the latter,
an edge 7 which is composed of two parallel sections 7' on
the lateral sides of the plate and of a dorsal edge 7 " .
The outer contour of the edge 7 corresponds to the oval
contour of the cover plate. On its side facing toward the
surface 6, the edge is provided with a profile ridge 8 and,
below the latter, with an undercut 8'. The connection pro-
file thereby formed on the inner side of the edge 7 runs in
a straight line in the lateral sections 7' and parallel on
both sides. In the dorsal section 7 " , the connection pro-
file is composed of two sections 9. In each of these sec-
tions, the connection profile runs in a straight line. The
profiles of both sections are arranged symmetrically with

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respect to the AP axis 10 of the implant and enclose an an-
gle a which, in the example shown, is 140°.
The top of the edge 7 forms a plane surface 6' which runs
parallel to the support surface 6 and likewise forms a sup-
port surface for the prosthesis core.
The flange 3 of the cover plate has a slit 11 which runs
perpendicular to the connection profile 6 and whose func-
tion is explained later.
On its top 12, the prosthesis core 5 forms a slide surface
which cooperates with the second cover plate (not shown) to
form a hinge. The contour of the prosthesis core is identi-
cal to that of the cover plate 1. On its underside, it has
a plane surface 13 which is intended to bear on the support
surface 6 of the end plate 1 and has substantially the same
contour shape. It is limited by a connection profile which
is formed by a profile ridge 14 and an undercut 14'. This
connection profile corresponds in a complementary manner to
the connection profile 8, 9 of the edge ridge 7 of the
cover plate 1. In particular, the connection profile is
composed of two lateral sections 15 and two dorsal sections
16 which correspond respectively to the lateral and dorsal
sections of the edge 7 of the cover plate 1 and can cooper-
ate with these in a form-fitting manner.
Outside the connection profile 14, 14', on the underside of
the prosthesis core 5 there is a plane surface 17 which
corresponds to the support surface 6' on the top of the
edge 7 of the cover plate 1 and cooperates with this when
the prosthesis core is mounted on the cover plate 1.
The prosthesis is assembled by means of the prosthesis core
being pushed with its connection profile 14, 14' into the

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corresponding connection profiles 8, 8' from the direction
of the open ventral side. When the prosthesis core has been
pushed in fully, its profile ridge 14 fits, not only in the
area of the lateral sections 7' but also in the area of the
dorsal section 7 " , into the undercut 8' of the edge 7 of
the cover plate, the connection profiles lying on one an-
other with substantially full-surface contact.
At the location where the slit 11 is situated in the gap 3,
the prosthesis core has a groove 18 which is flush with the
gap 11 when the prosthesis core has reached its end posi-
tion in which the dorsal connection profiles abut one an-
other. A plate (not shown) is pushed into the gap 11 and
the groove 18 and secures the prosthesis core in this posi-
tion relative to the cover plate 1. The plate is in turn
secured by means of also having a bore at the location of
the screw hole shown on the left in Fig. 3, through which
bore a fastening screw extends.
By virtue of the fact that the connection profiles of the
prosthesis core and of the cover plate are equipped, re-
spectively, with the sections 9 and 16 which each form a
triangle, it is possible, in comparison with known prosthe-
ses, to obtain increased stability of the position of the
prosthesis core relative to the cover plate 1. In particu-
lar, its stability with respect to relative movements in
the sense of rotation is thereby increased.

Representative Drawing