Intervertebral prosthesis with self-tapping fixing projections
An intervertebral prosthesis, in particular for the cervical spine, has two attachment plates connected in an articulated manner. The attachment surfaces of the attachment plates, which are configured for attachment to adjacent vertebral bodies have a base surface configured to bear on the surface of the vertebral bodies, and self-tapping fixing projections rising from the base surface. These fixing projections are formed by at least one pair of ribs which extend in opposite directions obliquely with respect to a predetermined implantation direction and whose side faces oriented more away from the implantation direction are steeper than their side faces oriented more in the implantation direction. The ribs can be toothed.
1 . An intervertebral prosthesis, comprising two attachment plates which are connected in an articulated manner and whose attachment surfaces configured for attachment to the adjacent vertebral bodies have a base surface configured to bear on surfaces of adjacent vertebral bodies, and self-tapping fixing projections rising from said base surface, wherein the fixing projections are formed by at least one pair of ribs which extend in opposite directions obliquely with respect to a predetermined implantation direction of the prosthesis and whose side faces oriented more away from the implantation direction are steeper than a slide-on surface oriented in the implantation direction.
2 . The prosthesis as claimed in claim 1 , wherein the implantation direction is an antero-posterior direction.
3 . The prosthesis as claimed in claim 2 , wherein the fixing projections are arranged symmetrically with respect to the median plane.
4 . The prosthesis as claimed in claim 1 , wherein the more ventrally oriented side face is substantially perpendicular to the base surface.
5 . The prosthesis as claimed in claim 1 , wherein the slide-on surface encloses an angle of less than 45° with respect to the base surface, measured in a plane extending parallel to the implantation direction and perpendicular to the base surface.
6 . The prosthesis as claimed in claim 1 , wherein the rib has a substantially uniform and constant profile, and its slide-on surface is formed by its more dorsally oriented side face.
7 . The prosthesis as claimed in one of claims 1 through 5 , wherein the rib is interrupted by a plurality of interruptions in order to form a series of pointed or sharp teeth.
8 . The prosthesis as claimed in claim 7 , wherein the interruptions extend in a sectional plane extending parallel to the base surface and perpendicular to the implantation direction.
9 . The prosthesis as claimed in claim 8 , wherein the teeth have a steep ventral flank and a dorsal flank less steep than the ventral flank.
10 . The prosthesis as claimed in claim 9 , wherein the teeth have a sawtooth-shaped profile, and their less steep, dorsal flanks form a slide-on surface.
11 . The prosthesis as claimed in claim 7 , wherein the interruptions extend in a sectional plane extending parallel to the base surface and parallel to the implantation direction.
12 . The prosthesis as claimed in claim 1 , wherein the proportion of the surface area taken up by the ribs is not greater than a fifth of the attachment surface.
13 . The prosthesis as claimed in claim 12 , wherein the cross-sectional surface area of the ribs in a sectional plane extending half way above the base surface is not greater than a tenth of the attachment surface.
14 . The prosthesis as claimed in claim 1 , wherein at least half of the surface area taken up by the ribs is at a distance of more than one sixth of the antero-posterior dimension of the attachment surface from the boundary of the attachment surface.
15 . The prosthesis as claimed in claim 1 , wherein the ribs at least of one rib pair approach one another in the dorsal direction.
16 . The prosthesis as claimed in claim 15 , wherein several ribs are arranged parallel to one another on each side of the plane of symmetry.
17 . The prosthesis as claimed in claim 1 , wherein the height of the ribs above the base surface is not greater than a tenth of the antero-posterior dimension of the attachment surface.
18 . The prosthesis as claimed in claim 1 , wherein an angle α enclosed by the more ventrally oriented side faces of the ribs in a sectional plane extending parallel to the base surface, is smaller than 60°.
19 . The prosthesis as claimed in claim 18 , wherein the angle α lies between 5 and 15°.
20 . The prosthesis as claimed in claim 9 , wherein the slide-on surface is roughened or toothed.
21 . The prosthesis as claimed in claim 1 , wherein at least one rib pair reaches at least as far as a fifth of the antero-posterior dimension of the attachment surface to the dorsal boundary thereof.
22 . The prosthesis as claimed in claim 18 , wherein the angle α enclosed by the more ventrally oriented side faces of the ribs in a sectional plane extending parallel to the base surface is smaller than 30°.