Deflection resistant acetabular cup

Abstract

An acetabular shell for use in hip arthroplasty. The shell includes a first wall having an outer surface, an inner surface, and a rim. The shell further includes a second wall extending from the outer surface of the first wall. The second wall has an outer surface, an inner surface, and a rim. The rim of the second wall is spaced outwardly from the rim of the first wall.

Claims

1. A method of manufacturing an acetabular shell comprising: manufacture a first wall of the acetabular shell, the first wall having an outer surface, an inner surface, and a rim, wherein the rim of the first wall extends continuously around an entire circumference of the outer and inner surfaces; manufacture a flexible second wall of the acetabular shell, the second wall having an outer surface, an inner surface, and a rim; cutting longitudinal recesses into the flexible second wall creating flanges, wherein the flanges of the flexible second wall are spaced around the circumference, wherein the longitudinal recesses extend to the rim of the second wall of the outer and inner surfaces of the second wall; slide the second wall of the acetabular shell over the first wall; and affix the second wall to the first wall such that the rim of the first wall is spaced apart from the rim of the flexible second wall.

2. The method of claim 1, wherein affixing the second wall to the first wall comprises affixing the second wall to the first wall via sintering.

3. The method of claim 1, wherein the manufacturing the first wall includes manufacturing an outer wall having a first radius and manufacturing the second wall comprises manufacturing an inner wall having a second radius, the second radius being larger than the first radius.

4. The method of claim 1, wherein the inner surface of the first wall includes a locking mechanism for locking a liner to the shell.

5. The acetabular shell of claim 4, wherein the locking mechanism includes a taper.

6. The acetabular shell of claim 4, wherein the locking mechanism includes a locking recess.

7. The acetabular shell of claim 1, wherein the outer surface of the first wall is convex.

8. The acetabular shell of claim 7, wherein the outer surface of the first wall has a first radius and the inner surface of the second wall has a second radius that is greater than the first radius.

9. The acetabular shell of claim 1, wherein the inner surface of the first wall is concave.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in connection with the accompanying drawings, in which:

(2) FIG. 1 is a perspective view of the acetabular shell according to one embodiment of the present invention;

(3) FIG. 2 is a cut-away view of the acetabular shell of FIG. 1;

(4) FIG. 3 is a top view of the acetabular shell of FIG. 1;

(5) FIG. 4 is a cut-away view of an assembly of the acetabular shell of FIG. 1 and an associated liner;

(6) FIG. 5 is a perspective view of the acetabular shell of FIG. 1 inserted into a simulated press-fit acetabulum; and

(7) FIG. 6 is a flow chart illustrating a method of manufacturing an acetabular shell according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(8) Embodiments of the present invention and the advantages thereof are best understood by referring to the following descriptions and drawings, wherein like numerals are used for like and corresponding parts of the drawings.

(9) Turning now to a FIG. 1, an acetabular shell (or cup) 10 is shown. The acetabular shell 10 includes a first wall 12 and a second wall 14 extending from the first wall 12. The second wall 14 is permanently fixed to the first wall 12. The first wall 12 has an outer surface 16, an inner surface 18, and a rim 20 coupling the two surfaces 16, 18. The second wall 14 includes an outer surface 22, an inner surface 24 (FIG. 2), and a rim 26 coupling the two surface 22, 24. The rim 26 of the second wall 14 is spaced outwardly from the rim 20 of the first wall 12. In other words, there is a recess 28 between the inner surface 24 of the second wall 14 and the outer surface 16 of the first wall 12. The recess 28 allows the second wall 14 to be deflected as it is inserted into a prepared acetabulum without deflecting the first wall 12. This will be more fully explained in detail below.

(10) As shown in FIG. 1, the second wall 14 may include a plurality of outwardly extending flanges 30. The flanges 30 are separated by longitudinal recesses 32. The flanges 30 and recesses 32 allow the second wall 14 to flex when inserted into a prepared acetabulum. In other embodiments, the second wall 14 may not include flanges 30 separated by recesses 32. In those embodiments, the second wall 14 may be a singular generally spherical wall that flexes when inserted into a prepared acetabulum.

(11) Turning now to FIG. 2, a sectioned view of the acetabular shell 10 is shown. As shown, the second wall 14 extends outwardly from the inner wall 12, creating the recess 28. Also, as shown in this embodiment, the rim 20 of the first wall 12 extends lower than the rim 26 of the second wall 14. In some acetabular shell designs, it is desired to have the first wall 12 extend further than the second wall 14 for increased taper engagement of a liner 34 (FIG. 4). In other embodiments, the rims 20, 26 may be in the same plane. In other embodiments, the rim 26 of the second wall 14 may extend lower than the rim 20 of the first wall 12.

(12) The inner surface 18 of the first wall 12 is concave and designed to mate with a liner 34 (FIG. 4). The inner surface 18 includes a locking mechanism 36, which in this embodiment includes a taper 38 and a locking recess 40. The locking mechanism 36 interacts with corresponding features on the liner 34 to lock the liner 34 into the shell 10. In other embodiments, different types of locking mechanisms may be used, for example, only a taper may be used or only a locking ring may be used. In other embodiments, other known locking mechanisms may be used, such as threaded locks, screws, pins, etc. . . .

(13) The outer surface 16 of the first wall 12 is illustrated as being spherical. In certain other embodiments however, the outer surface 16 may be cylindrical in shape. As shown in FIG. 3, the outer surface 16 (whether cylindrical or spherical) has a radius r1. The radius r1 is less than a radius r2 of the inner surface 24 of the second wall 14. The difference between r1 and r2 is the amount that the second wall 14 can be compressed before the first wall 12 is affected. The outer surface 22 of the second wall 14 has a radius r3 that is sized to fit into a prepared acetabulum. As the inner surface 18 of the first wall 12 is designed to mate with a liner 34 as described above, it will have a radius r4 that corresponds to a radius of the liner 34. In some embodiments, a plurality of shells 10 will be provided, having a variety of radiuses r3 to fit into a wide variety of acetabulums. Also, the radius r4 of the inner surface 18 of the first wall 12 may also vary within a set of shells 10 so as to accommodate different liners 34.

(14) FIG. 4 illustrates a shell 10 with a liner 34 assembled into it. As shown, the liner 34 includes a locking mechanism 42 that corresponds with the locking mechanism 36 of the shell 10. In this embodiment, the locking mechanism 42 includes a taper 44 corresponding to the taper 38 of the shell and a locking ring 46 that locks into the locking recess 40 of the shell 10. In some embodiments, the locking mechanism 42 may only include a taper 44 or a locking ring 46, but not both. In yet other embodiments, the taper 44 may not lock into the taper 38 of the shell. The tapers 38, 44 may only be matching tapers so as to allow ease of insertion. In other embodiments, other types of locking mechanisms may be used.

(15) Turning now to FIG. 5, the shell 10 is shown inserted into a simulated press-fit acetabulum 48. As shown, the simulated acetabulum 48 compresses the second wall 14 of the shell 10. As shown in FIG. 5, flange 50 of the second wall 14 is a distance D1 from the inner wall 18. Flange 52 of the second wall 14 is a distance D2 from the inner wall 18. In an uncompressed state, D1 is approximately the same as D2. However, as the second wall 14 is compressed, by the acetabulum 48, D2 becomes less than D1. Even during compression, the inner (or first) wall 12 remains unchanged. Thus, when a liner 34 is inserted, which may be before the insertion of the shell 10 into the acetabulum 48 or after, the locking taper 38 and locking recess 40 are not affected.

(16) Turning now to FIG. 6, a method of manufacturing a shell according to one embodiment of the invention will be described. The first wall 12 is manufactured using known methods at step s100. In one embodiment, the first wall 12 is machined. However, other known methods may also be used. At step s102, the second wall 14 is manufactured and then slid onto the first wall 12 (step s104). The second wall 14 is affixed to the first wall 12 via a sintering process or through the addition of an outer porous coating to the shell (step s106). In other embodiments, the first and second walls may be welded together or attached via fasteners.

(17) In other embodiments, the shell 10 may be manufactured as a single piece. The recess 28 may then be cut into the shell 10, creating the first and second walls 12, 14.

(18) In the present embodiment, the shell 10 is made of biocompatible metal, such as titanium, cobalt chrome, stainless steel. The shell 10 may also be made with porous metal, such as GRIPTION, manufactured by DePuy, Inc. of Warsaw, Ind. As discussed above, the shell 10 may have a sintered coating, such as POROCOAT, manufactured by DePuy Orthopaedics, Inc. of Warsaw, Ind. Other known porous coatings and materials may also be used. In yet other embodiments, the shell may be made of biocompatible ceramic or plastics, such as ultrahigh molecular weight polyethylene (UHMWPE) or polyether ether ketone (PEEK). In some embodiments the first and second walls 12, 14 are made of the same materials. In other embodiments, the first and second walls 12, 14 may be made of different materials. In those embodiments, the first wall 12 may be made of a stiffer material and the second wall 14 may be made of a more flexible material.

(19) In some embodiments, the liner 34 may be made of biocompatible metals, such as titanium, cobalt chrome, and stainless steel. In other embodiments, the liners 34 may be made of biocompatible polyethylene such as UHMWPE, polyethylene with antioxidants (including UHMWPE with antioxidants), and PEEK. The liners 34 may also be made of biocompatible ceramics, as are known in the art.

(20) While the invention is susceptible to various modifications and alternative forms, a specific embodiment thereof has been shown by way of example in the drawings. It should be understood, however, that there is no intent to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.