Abstract
An outer shell (1) for a joint socket implant, in particular for an acetabular implant, which comprises a convex outer face (3) and a concave inner face (4) for receiving an inner shell. The concave inner face (4) has at least partially a toothing system (7), in particular a circular circumferential region (6) thereof. Via the toothing system (7), an inhibition of the rotatability of the two shells, relative to one another, can be achieved upon insertion of the inner shell into the outer shell (1).
Claims
1. A joint socket implant, comprising: an outer shell with a convex outer face and a concave inner face, which has a toothing system in a circular circumferential region, wherein flanks of the toothing system are oriented parallel to a longitudinal central axis of the outer shell, a tooth profile has a tooth height defined as the difference between a radius of a tip circle and a radius of a root circle of the toothing system, an inner shell inserted into the outer shell, a hardness of the outer shell is greater than that of the inner shell, the region of the inner shell coming into contact with the toothing system has a size, relative to the tip circle of the toothing system, such that an inhibition of the rotatability of the two shells, relative to each other, is achievable by the material of the inner shell being displaced by the toothing system, wherein a hollow space remains between the flanks of adjacent teeth and the inner shell inserted into the toothing system.
2. The joint socket implant as claimed in claim 1, wherein the outer shell is produced from titanium or from a titanium-based, steel-based, cobalt-based or zirconium-based alloy.
3. The joint socket implant as claimed in claim 1, wherein the inner shell is produced from a polyethylene.
4. The joint socket implant as claimed in claim 3, wherein the polyethylene is one of polyethylene of ultra-high molecular weight (UHMWPE), highly crosslinked polyethylene (HCPE), polyetheretherketone (PEEK) or polyaryletherketone (PAEK).
5. The joint socket implant as claimed in claim 1, wherein the toothing system extends continuously about the circular circumferential region.
6. The joint socket implant as claimed in claim 1, wherein the outer shell and the inner shell have corresponding axial locking elements via which they are locked onto each other relative to the common longitudinal central axis.
7. The joint socket implant as claimed in claim 6, wherein the circumferential region with the toothing system is arranged in a cylindrical portion of the concave inner face of the outer shell adjacent to the corresponding locking elements, relative to the common longitudinal central axis.
8. The joint socket implant as claimed in claim 1, wherein the toothing system penetrates into the material of the inner shell with a tooth penetration depth of between 0.1 and 1.0 mm.
9. The joint socket implant as claimed in claim 8, wherein the total number of teeth of the toothing system and a width of the teeth, relative to the longitudinal central axis, are chosen in such a way that inhibition of the rotatability exceeds a predefined setpoint torque.
10. The joint socket implant as claimed in claim 1, wherein the individual teeth of the toothing system enclose an angle of 45 to 100.
11. The joint socket implant as claimed in claim 9, wherein side flanks of the teeth are planar surfaces.
12. The joint socket implant as claimed in claim 1, wherein the toothing system extends only partially about the circular circumferential region.
13. The joint socket implant as claimed in claim 1, wherein the circumferential region with the toothing system, relative to the central longitudinal axis, lies closer to an equator of the outer shell than to a pole.
14. The joint socket implant as claimed in claim 1, wherein the inner shell is made of a plastic material with a Shore hardness (D) of between 50 and 85.
15. The joint socket implant as claimed in claim 1, wherein the toothing system is capable of transmitting a torque greater than 10 Nm.
Description
(1) Further advantages and individual features of the invention will become clear from the following description of an illustrative embodiment and from the schematic drawings, in which:
(2) FIG. 1 shows a perspective view of an outer shell for a joint socket implant;
(3) FIG. 2 shows a perspective view of an inner shell for use with an outer shell;
(4) FIG. 3 shows a plan view of an outer shell;
(5) FIG. 4 shows an enlargement of the subregion B according to FIG. 3;
(6) FIG. 5 shows a schematic enlargement of the subregion D according to FIG. 4;
(7) FIG. 6 shows a sectional view of an outer shell through the section plane A according to FIG. 3;
(8) FIG. 7 shows an enlargement of the subregion C according to FIG. 6;
(9) FIG. 8 shows a perspective view of an inner shell inserted into an outer shell;
(10) FIG. 9 shows a sectional view of an inner shell inserted into an outer shell;
(11) FIG. 10 shows a sectional view of an alternative illustrative embodiment of an outer shell;
(12) FIG. 11 shows a sectional view of an alternative illustrative embodiment of a joint socket implant using the outer shell according to FIG. 10;
(13) FIG. 12 shows an enlargement of the subregion E according to FIG. 10;
(14) FIG. 13 shows an enlargement of the subregion F according to FIG. 11;
(15) FIG. 14 shows an enlargement of the partial section through the plane G according to FIG. 11, and
(16) FIG. 15 shows a perspective and schematic view of the engagement of two teeth of a toothing system into the material of the inner shell.
(17) As will be seen from FIG. 1, an outer shell 1 for a joint socket implant 2 (FIG. 9) has a convex outer face 3 and a concave inner face 4. The inner face 4 has a circular circumferential region 6 which is provided with a toothing system 7.
(18) As will be seen from FIG. 2, an inner shell 5 for a joint socket implant 2 according to the invention has, on its concave inner face, a joint-bearing surface 19. The convex outer face 15 is divided into different subregions. Near the equator, the inner shell 5 shown has a conical region 16 and, at the edge region thereof near the pole, a locking element 17 is arranged. A projection 18 is mounted at the pole of the inner shell 5. Both the conical region 16 and the projection 18 serve to prevent tilting of the inner shell 5 in the outer shell 1.
(19) It is clear from FIG. 3 that, in the illustrative embodiment shown, the toothing system 7 is arranged relatively far to the outside on the concave inner face 4 of the outer shell 1. Here, the radius r of the root circle 12 of the toothing system 7 is ca. 70% of the total radius R of the outer shell 1.
(20) It will be seen from FIG. 4 that a triangular tooth profile is used for the toothing system in the illustrative embodiment under discussion, the triangles being spaced slightly apart from one another.
(21) FIG. 5 is a schematic representation of the tooth profile according to FIG. 4. The root circle 12 and the tip circle 14 are plotted with broken lines in the tooth profile. The angle enclosed by the tooth profile is likewise indicated. It will moreover be seen that the height h of the tooth profile is defined as the difference between the radius of the tip circle 14 and that of the root circle 12.
(22) Further details of the outer shell 1 according to the invention will be evident from the sectional view according to FIG. 6. This shows that the concave inner face 4 of the outer shell 1 is divided into different regions. Thus, the region 10, in which the axial locking element 8 equipped with the toothing system 7 is also arranged, has a stepped configuration. By contrast, the region 11 is shaped conically. The outer shell 1 has an opening 13 at its pole. The longitudinal central axis of the outer shell is designated by S.
(23) FIG. 7 shows the configuration of the locking element 8 provided with a toothing system 7. It will be seen that the toothing system 7 has the width b which, in the present illustrative embodiment, is identical to that of the locking element. It will moreover be seen that the toothing system 7 here has a trapezoid transverse profile.
(24) FIG. 8 shows a perspective view of a joint socket implant 2 according to the invention with outer shell 1 and inner shell 5. The joint-bearing surface 19 on the concave inner face can be seen in particular. FIG. 9 shows a longitudinal section through said joint socket implant 2. It will be seen that the projection 18 at the pole of the inner shell 5 engages in the opening 13 provided for it in the outer shell 1. The common main axis (longitudinal central axis) of outer shell and inner shell is designated by SS.
(25) FIGS. 10 and 11 show a modified illustrative embodiment of a joint socket implant, in which the outer shell has another inner contour. In contrast to the outer shell according to FIG. 6, the toothing system 7 is arranged in another region. The conical inlet region 11 on the inner face 4 is followed by a likewise conical undercut 21, of which the configuration can be seen more exactly in FIG. 12. The shoulder 22 between the undercut 21 and the conical region 11 forms the locking element of the outer shell, behind which locking element a corresponding material shoulder 23 of the inner shell engages with a locking action (FIG. 13). Directly below the undercut 21 is a circumferential cylindrical region at which the toothing system 7 is arranged. The toothing system extends over the width b, hence not over the entire cylindrical region. In contrast to the inner shell according to FIG. 9, the inner shell according to FIG. 11 has no material projection that engages in the opening 13. The situation in the region of the locking connection and of the toothing system can be seen more exactly in FIG. 13. Accordingly, a cylindrical region on the inner shell is oversized in relation to the tip circle of the toothing system, such that, depending on material tolerances, a penetration depth e of the individual teeth into the material of the inner shell 5 is obtained. This penetration depth is shown again in FIG. 14, where the tooth flanks enclose between them an angle of 90. The flank angle determines the tooth thickness d in the region of the root circle 12, and the distance between two teeth in the region of the tip circle 14 is indicated by the dimension a. It will be seen clearly from FIG. 15 that, after the inner shell 5 has been pressed in, a hollow space 24 remains between two tooth flanks, which hollow space 24 has to be of a sufficiently large dimension to ensure that the material of the inner shell displaced by the teeth can escape.
(26) The main parameters of the toothing system are shown schematically again in FIG. 15. The penetration depth e should not exceed 0.1 mm to 1 mm. It is desirable to have the largest possible number of teeth 25 at a uniform distance a from each other. These teeth have a height h, wherein a difference remains between e and h, such that a hollow space 24 remains between adjacent tooth flanks 9. b is the width of the toothing system or, more precisely, the width of the penetration of the individual teeth into the material of the inner shell 5. As mentioned at the outset, the transmissible torque increases the greater the width b of the toothing system, at a given penetration depth e. By contrast, the pressing-in force is determined substantially by the penetration depth e. The required dimensions of the toothing system are determined, for different shell sizes, on the basis of a torque predefined by medical standards, e.g. a torque of greater than 12 Nm, that the inner shell has to be able to transmit to the outer shell.
