Bipolar hip prosthesis with locking head

Abstract: An articulating prosthesis (10) includes a cup (12) having a shell (24) and a liner (26) and at least one resilient locking element (48). The shell (24) has a spherical outer surface (22) that may be adapted to articulate with an acetabulum and the liner (26) has a spherical inner surface (20) that forms an articulation surface for the spherical head (18) of a stem member (14). The resilient locking member (48) extends inward toward a longitudinal axis (30) of the cup (12) and at least partially in a superior direction. The resilient locking element (48) defines a nominal first diameter (56) expandable to a larger second diameter (58) in response to a force and is returnable to the first diameter (56) in the absence of the force for securing the head (18) of a stem prosthesis member (14).

Description: The present invention relates to an articulating prosthesis having a locking element. BACKGROUND OF THE INVENTION In a hip hemiarthroplasty procedure, the proximal portion of a femur is replaced with a suitable prosthetic hip joint implant or implant assembly that articulatably mates directly with a patient's natural acetabulum. Two types of femoral prostheses are typically suitable for hip hemiarthroplasty procedures. One type is a bipolar prosthesis. In general, a bipolar hip prosthesis, such as disclosed in U.S. Patent Nos. 3,813,699 and 3,863,273, includes a shell having an external surface which articulates with a patient's acetabulum and an internal surface which articulates with the spherical head member of a prosthetic femoral component. The other type of prosthesis is often referred to as a unipolar endoprosthesis in which the prosthetic femoral component includes a spherical head member which is large enough to articulate directly with the acetabulum. One drawback to the successful use of bipolar hip prostheses is that they may become displaced after insertion. In particular, the spherical head of the femoral component may become dissociated from the shell. Such a dissociation may occur as the result of the abnormal twisting of a leg, or after a trauma such as a fall, such as might cause a dislocation in a natural hip joint. A problem with some prior art bipolar hip prostheses is that, in these situations, the dissociation can only be cured by further surgery. United States Patent No. 4,798,610 describes a bipolar femoral hip prosthesis having a floating locking ring that attempts to provide improvements over U.S. Patent No. 4,241,463. According to its disclosure, the spherical head of this femoral prosthesis does not dislocate from the shell. Rather, in response to forces that would dislocate a natural hip, the shell disengages from the acetabulum. The dislocation may then be corrected in a manner similar to the manner in which the dislocation of a natural hip is corrected. Dissociation of the components within the acetabulum is not necessarily preferred however. When correcting such a dissociation, it can be difficult to properly align the shell during correction. Also, dissociation of the components within the acetabulum and correction of such a condition can result in damage to the patient's natural bone. In addition, proper orientation of a floating locking ring, such as those described in U.S. Patent Nos. 4,241,463 and 4,798,610, can be problematic, even during normal use of the prosthesis. US 4,044,403 and US 4,172,296 each disclose an articulating joint prosthesis comprising a first member having a substantially spherical head, and a second member comprising a cup received in a shell. The shell has an outer surface adapted for implantation in a skeletal cavity, and an inner surface. The cup has an outer surface that is congruent with the inner surface of the shell, and an inner surface adapted to receive the head of the first member. The cup is provided with a groove to define a resilient locking element which is inwardly deformable during insertion of the spherical head into the cup and which is outwardly deformable to resist escape of the head from the cup. US 4,172,296 further discloses a detent in the shell for engaging another groove in the cup to secure the cup within the shell. US 5,263,988 discloses a prosthesis assembly comprising a shell, an insert and a locking ring adapted to lock the assembly together. The locking ring is slotted to facilitate insertion of a femoral head prosthesis into a cavity in the insert. The locking ring also includes barbs shaped to mate with recesses in the shell to resist accidental disassembly of the device. SUMMARY OF THE INVENTION According to the invention, there is provided an articulating hemiarthroplasty prosthesis as set forth in claim 1 of the accompanying claims. Further features are set out in the accompanying dependent claims 2 to 18. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: FIG. 1 is a side view of an articulating prosthesis of the invention having an articulating cup and an endoprosthesis component; FIG. 2 is an inferior view of an articulating cup of the invention; FIG. 3 is a cross sectional view of the cup of FIG. 2 taken along line 3-3; FIG. 4 is a cross sectional view of the cup of FIG. 2 taken along line 4-4; FIG. 5 is an exploded view of a spherical head of an endoprosthesis component partially inserted into the articulating cup of FIG. 2; and FIG. 6 is an exploded view of the spherical head and articulating cup of FIG. 5 with the head fully inserted. DETAILED DESCRIPTION OF THE INVENTION An articulating prosthesis 10 of the invention is illustrated in FIG. 1 as an articulating cup 12 in association with a proximal femoral endoprosthesis 14. The endoprosthesis 14 includes a stem portion 16 which is received within the medullary canal of a femur and a spherical head 18 which is articulatably matable with the articulating cup 12. The articulating cup 12 has a spherical inner surface 20 which is articulatably matable with the spherical head 18 and a substantially spherical outer surface 22 which is articulatably matable with a natural acetabulum. As shown in FIGS. 2 to 4, the articulating cup 12 may be provided in several distinct pieces including a shell 24, a liner 26 and a locking liner portion 28. The cup 12 also includes a longitudinal axis 30, a superior apex 32 and an inferior aperture 34. The shell 24 is preferably formed from a biocompatible metal such as titanium, a titanium alloy or a stainless steel, and has an inner surface 36 and a spherical outer surface 22 adapted to articulate with a natural acetabulum. The outer surface 22 of shell 24 should be sized according to the size of the patent's acetabulum, and generally will have a diameter between about 36 and 80 millimeters. The liner 26 is preferably formed from a polymeric material, such as ultra high molecular weight polyethylene. The liner 26 has an outer surface 38, which matable to the inner surface 36 of the shell 24. The liner 26 also has a spherical inner surface 20 which is suited to articulate with the spherical head 18 of a femoral endoprosthesis 14. Preferably, the spherical inner surface 20 of the liner 26 covers no more than one half of a sphere. In the embodiment of FIGS. 3-4, the inner surface 20 of the liner 26 is hemispherical and the liner 26 is seated wholly within the shell 24. The locking liner portion 28 may also be formed from a polymeric material such as ultra high molecular weight polyethylene. As shown in FIGS. 3-4, the locking liner portion 28 has a superior surface 40 that abuts the liner 26 within the shell 24. The locking liner portion 28 also has an inferior-facing, circumferential ledge 42 which abuts a similar, circumferential opposed ledge 44 provided on the inner surface 38 of the shell 24 proximate to the inferior aperture 34. The interlocking of the ledges 42, 44 secures the locking liner portion 28 against dissociation from the shell 24. In the embodiment of FIGS. 3 and 4, a portion of the superior surface 40 of the locking liner portion 28 also abuts an inferior facing ledge 46 on the inner surface 38 of the shell 24. In this embodiment, the locking liner portion 28 remains in its intended position and orientation within the shell 24 even if, for some reason, the liner 26 does not. As shown in FIGS. 3 and 4, a locking element 48 extends from the locking liner portion 28. The locking element 48 is disposed around the periphery of the locking liner portion 28 proximate to the inferior aperture 34 of the cup 12 and extends inward, toward the longitudinal axis 30 of the cup 12, and in a superior direction toward the superior apex 32 of the cup 12. In the disclosed embodiments, the locking element 48 extends from the liner locking portion 28, however, a person of ordinary skill in the art will recognize that other configurations are possible. Generally, the locking element 48 preferably extends from a region 50 adjacent to the shell 24 and in proximity to the inferior aperture 34. In addition, the locking element 48 need not be disposed continuously around the periphery of the inferior aperture 34, but may consist of a plurality of discrete locking elements. The locking element 48 is resilient and may be deformed in response to an insertion force directed from the inferior aperture 34 towards the superior apex 32, such as the insertion force provided by the insertion of the spherical head 18 of a femoral endoprosthesis 14 into the inferior aperture 34 of the cup 12. A peripheral groove 52 is disposed on the superior side 54 of the locking element 48 to provide clearance for the locking element 48 to deform. Longitudinal grooves 55 may also be provided to aid in the deforming of the locking element 48. In response to an insertion force, the locking element 48 deforms from a first position (FIGS. 3 and 4) defining a first nominal diameter 56, outward and away from the longitudinal axis 30 of the cup 12 to define a second, larger diameter 58 (FIG. 5). The resilient locking element 48 then returns to its first position upon removal of the insertion force, such as when the spherical head 18 of a femoral endoprosthesis has been inserted past the locking element 48 to engage the spherical inner surface 20 of the liner 26 (FIG. 6). A head contacting portion 60 of the locking element 48 may be a spherical surface portion that, when the locking element is in its first position, defines a surface portion on a projection of the spherical inner surface 20 of the liner 26. In this way, the head contacting portion 60 will contact the spherical head 18 along a contact region. A person of ordinary skill in the art will understand, however, that other head contacting portion 60 configurations may be used, included including a rounded contacting portion (not shown) that contacts the spherical head 18 only at a point, or along a line around the periphery of the inferior aperture 34. Generally, the spherical head 18 will have a diameter 62 between about 22 and 32 millimeters. The first nominal diameter 54 is smaller than the diameter 62 of the spherical head 18, but the locking element 48 deforms to a second, larger diameter 56 that is at least as large as the diameter 62 of the spherical head 18. In this way, the head 18 deforms the locking element 48 upon insertion into the cap 12, passes through the locking element 48, and articulatably engages the inner surface 20 of the liner 26 as the locking element 48 returns to its original position. Once the spherical head 18 is fully inserted into the cup 12 and the locking element 48 returns to its original position, the head contacting portion 60 of the locking element 48 contacts the spherical head 18 to keep the spherical head 18 in contact with the spherical inner surface 20 of the liner 26 and to prevent dissociation of the head 18 from the cup 12. Sbould dissociation occur, the head 18 may be reinserted into the cup 12 by properly orienting the head 18 and providing an insertion force to push the head 18 through the locking element 48 as shown in FIGS. 5 and 6. Due to the structure of the locking element 48 of the invention, the insertion force required to insert or reinsert the head 18 into the cup 12 is less than the subluxation force required to dissociate the head 18 from the cup 12 - making the head 18 difficult to dissociate from the cup 12, but making it easy to reinsert the head 18 should dissociation occur. Although the present invention is described with respect to particular embodiments and features and uses, numerous variations or equivalents are possible without taking away from the scope of the claimed invention.

Claims: An articulating hemiarthroplasty prosthesis (10) comprising: a shell (24) having a spherical outer articulation surface (22) for articulating with an acetabulum and an inner surface (36), a longitudinal axis (30), an inferior aperture (34) and a superior apex (32), a liner (26) mateable with the inner surface (36) of the shell in proximity to the superior apex (32) of the shell and having a spherical inner surface (20) for articulating with a prosthetic femoral head (18), and a locking liner element (28) disposed within the shell (24) and mateable with the inner surface (36) of the shell in proximity to the inferior aperture (34), the locking liner element (28) including at least one resilient locking element (48), integral therewith and extending from a region (50) proximate to the inferior aperture (34) of the shell inward toward the longitudinal axis (30) of the shell and at least partially in a superior direction toward the apex (32) of the shell, the resilient locking element (48) being deformable, in response to an insertion force directed from the inferior aperture (34), from a first position, defining a first nominal diameter (56), outward away from the longitudinal axis (30) of the shell to define a second, larger diameter 58, wherein the locking liner element (28) has a superior surface (40) that abuts an inferior surface (46) of the liner (26) and the locking liner element (28) includes an inferior facing surface (42) that abuts a superior facing surface (44) formed in the inner surface (36) of the shell to hold the locking liner element (28) against inferior movement with respect to the shell (24), characterised by the locking liner element (28) further comprising a groove (52) formed in the liner element (28) adjacent to a superior surface (54) of the at least one resilient locking element (48), the groove (52) providing clearance for the resilient locking element (48) to deform in response to an insertion force directed from the inferior aperture (34). The prosthesis of claim 1, wherein the resilient locking element (48) returns to its first position upon removal of the insertion force. The prosthesis of claim 1, wherein the at least one locking element (48) has a spherical surface portion (60) that, when the at least one locking element (48) is in its first position, defines a surface portion on a projection of the spherical inner surface (20) of the liner (26). The prosthesis of claim 1, further comprising a stem member (16) having a spherical head (18) adapted to fit with and to articulate with the spherical inner surface (20) of the liner (26). The prosthesis of claim 4, wherein the spherical head (18) has a diameter (62) larger than the first nominal diameter (56) defined by the locking element (28). The prosthesis of claim 4 or claim 5, wherein the spherical head (18) is sized so as to deform the locking element (28) from its first position to its second position in response to an insertion force applied to the spherical head (18), an inferior direction, allowing the spherical head (18) to pass through the second, larger diameter (58) of the locking element (28) and to articulatably engage the spherical inner surface (20) of the liner (26), the spherical head (18) further being sized so as to allow the resilient locking element (28) to return to its first, nominal diameter (56) after the spherical head (18) has engaged the inner surface (20) of the liner (26). The prosthesis of claim 6, wherein the insertion force required to insert the spherical head (18) through the inferior aperture (34) to deform the at least one locking element (48) and engage the inner surface (20) of the liner (26) is smaller than a subluxation force required to remove the spherical head (18) from its engagement with the inner surface (20) of the liner (26). The prosthesis of claim 4, wherein the articulating prosthesis (10) is a bipolar, hemiarthroplasty hip prosthesis. The prosthesis of claim 8, wherein the stem (16) is matable with a femur. The prosthesis of claim 8, wherein reinsertion of the spherical head (18) into the shell (24) following subluxation of the spherical head (18) from the shell (24) after installation of the prosthesis within a patient may be performed without surgery. The prosthesis of any preceding claim, wherein the at least one locking liner element (28) extends around a perimeter of the aperture (34). The prosthesis of claim 11, wherein the groove (52) extends around the perimeter of the aperture (34). The prosthesis of claim 12, wherein at least one longitudinal groove (55) is formed in the locking liner element (28). The prosthesis of claim 6, wherein the spherical head (18) has a diameter that is substantially equal to a diameter of the spherical inner surface (20) of the liner, the value of each diameter being between about 22 and 32 millimeters. The prosthesis of any preceding claim, wherein a diameter of the spherical outer surface (36) of the shell is between about 36 and 80 millimeters. The prosthesis of any preceding claim, wherein the locking element (28) is made from ultra high molecular weight polyethylene. The prosthesis of claim 16, wherein the shell is made from a metal. The prosthesis of any preceding claim, wherein the spherical inner surface (20) of the liner (26) covers no more than one half of a sphere.

Inventors: KHALILI FARID BRUCE, OCHOA JORGE, KHALILI, FARID BRUCE, OCHOA, JORGE
Applicants: DEPUY PRODUCTS INC, DEPUY PRODUCTS, INC.
Application year: 1999
Main classification: A61F2
IPC codes: A61F2