Bipolar hip prosthesis with locking head

Details Bipolar hip prosthesis with locking head Bipolar hip prosthesis with locking head

1998-03-27

2001-03-27

Willse, David H. (Department: 3738)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Implantable prosthesis

Bone

C623S022260

Reexamination Certificate

active

06206929

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable.
FIELD OF THE INVENTION
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. Pat. 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.
U.S. Pat. No. 4,798,610 describes a bipolar femoral hip prosthesis having a floating locking ring that attempts to provide improvements over U.S. Pat. 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. Pat. Nos. 4,241,463 and 4,798,610, can be problematic, even during normal use of the prosthesis.
SUMMARY OF THE INVENTION
The present invention provides an articulating prosthesis having a cup and at least one resilient locking element. The cup includes a shell having a spherical outer surface shaped so as to articulate with a natural acetabulum and has a superior apex and an inferior aperture. A liner is provided on the inner surface of the shell. The liner, which may be formed from a polymeric material such as ultra high molecular weight polyethylene, has a spherical inner surface. The locking element is resilient and is disposed at least partially within the shell. The locking element extends inward, toward a longitudinal axis of the cup, and at least partially in a superior direction toward the apex of the cup.
The locking element deforms, in response to an insertion force directed from the inferior aperture from a first position, defining a first nominal diameter, outward and away from the longitudinal axis of the cup to define a second, larger diameter. When the insertion force is removed, the resilient locking member returns to its original position. An end of the locking element may define a surface portion on a projection of the spherical inner surface of the liner when the locking element is in its first position.
The articulating prosthesis may also include a stem member having a spherical head adapted to fit within and articulate with the spherical inner surface of the liner. The spherical head is sized so as to deform the locking element from its first position to its second position in response to an insertion force applied to the spherical head from an inferior direction, allowing the spherical head to pass through the second, larger diameter of the locking element and to articulatably engage the spherical inner surface of the liner. The spherical head is also sized so as to allow the resilient locking element to return to its first, nominal diameter after the spherical head has engaged the inner surface of the liner.


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