Anti-impingement femoral prostheses

Details Anti-impingement femoral prostheses Anti-impingement femoral prostheses

1999-10-01

2001-03-13

Isabella, David J (Department: 3738)

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

Implantable prosthesis

Bone

C623S023350

Reexamination Certificate

active

06200350

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to orthopaedic surgery and, more particularly, to a proximal femoral prosthesis facilitating an enhanced range of motion.
BACKGROUND OF THE INVENTION
In total hip arthroplasty, the defective head and neck of the proximal femur are removed and replaced with a prosthetic element. Although extramedullary units are available, intramedullary prostheses are more commonly employed, which feature an elongated stem adapted for insertion and fixation within the femoral canal.
FIG. 1
is a generalized representation of a prior-art proximal femoral endoprosthesis. A head portion
102
having an outer surface
103
which is at least partially hemispherical is joined to a stem
106
through a neck portion
104
. Such interconnections may be permanent and integral, or modular connections may be used in conjunction with tapered metal joints, for example.
The stem
106
defines a first axis
108
which is aligned more or less to the longitudinal axis of the femur, depending upon the style of the particular implant. The neck
104
defines a second axis
110
which intersects with the first axis
108
at a neck/shaft angle which may be varied in accordance with the physiology of the recipient or the desires of a given manufacturer. A typical neck/shaft angle &agr; is on the order of 135°. The offset, or distance from the head portion to the axis of the stem, may also varied to achieve a desired result. A number of other variations exist, including cemented versus cementless interfaces, curved versus straight stem profiles, differently sized balls, and so forth.
In all existing configurations, the neck is straight or, in some cases, curved upwardly (or proximally) away from a plane transverse to the axis of the stem. That is to say, a centroid drawn from a central region
112
of the head
102
to a point of intersection
111
with the stem axis
108
is straight or occasionally curved to create a convex neck surface in existing designs. Such a configuration has several shortcomings. For one, as manufacturers decrease the neck-shaft angle &agr; to improve offset and abductor tension, patients lose movement in flexion secondary to impingement of the neck on the acetabular component.
SUMMARY OF THE INVENTION
This invention resides in proximal femoral prostheses which minimize impingement, thereby affording an enhanced range of motion as compared to existing devices. Broadly, the central portion of the neck of the inventive prosthesis is oriented downwardly relative to a straight line drawn between the ball portion and the point of interconnection to the exposed portion of the stem. Such a configuration reduces impingement in flexion/internal rotation and extension/external rotation, assuming an appropriately placed acetabular component. In the preferred embodiment, the neck is curved between the head and the neck, though, in alternative embodiments, the neck may be provided in straight and/or modular segments. The invention is compatible with neck-shaft angles, offsets, head sizes, and other dimensions commonly designated with respect to available implants. The neck may also be curved in the transverse plane adding increased anteversion or retroversion to the neck-shaft relationship.


REFERENCES:
patent: 4822370 (1989-04-01), Schelhas
patent: 4938770 (1990-07-01), Frey et al.
patent: 4957510 (1990-09-01), Cremascoli
patent: 4978359 (1990-12-01), Wilhelm et al.
patent: 5387244 (1995-02-01), Breard
patent: 5580352 (1996-12-01), Sekel
patent: 5876459 (1999-03-01), Powell

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