Multipolar Joint Endoprosthesis

Various joint endoprostheses have previously been proposed. While generally satisfactory for the purpose of orthopaedic joint replacement, they have been found unsatisfactory for a number of reasons: dislocation, dissociation of components, bony wear, acetabular protrusio, pain, polyethylene wear, limited range of motion, etc.

It is therefore an object of the present novel invention to provide a joint endoprosthesis which overcomes the disadvantages of prior systems as set forth above.

It is further an object of the present invention to be highly effective and reliable in its operation.

The multipolar joint endoprosthesis presented consists of multiple wedge-shaped, cylindrical components that are inseparable except by surgical manipulation, but rotate freely about an axis perpendicular to their planes of effacement with adjacent components. In addition to the components described, two additional components are included: (1) a component, herein known as the proximal component, contoured to fit the proximal side of the surgically prepared joint (i.e. the glenoid fossa of the gleno-humeral joint, the acetabulum of the hip, etc.) and (2) a component, herein known as the distal component, contoured to fit the distal side of the surgically prepared joint or into the surgically prepared intramedullary canal distal to the involved joint (i.e. intramedullary canal of the humerus, hip, etc.). The proximal and distal components similarly rotate about an axis perpendicular to their planes of effacement with the wedge shaped components. The proximal and distal components are also inseparable from the other components except by surgical manipulation. The proximal and distal components can be firmly affixed to their corresponding bony landmarks utilizing methylmethacrylate bone cement, screws, bony ingrowth, etc.

Since the planes of effacement of each wedge-shaped component are non-parallel and converging, passive rotation of one or more of the wedge-shaped components alters the angle of orientation between the proximal and distal components, thereby allowing for range of motion in all directions of the bony structures to which the proximal and distal components are attached.

Since there is no motion at the bone-prosthesis interfaces, it is hypothesized that many of the problems of previously proposed endoprostheses would be resolved (i.e. bony wear, acetabular protrusio, pain, etc.). In addition, the components are inseparable except by surgical manipulation, as noted above, avoiding the problems of dislocation, dissociation of components, etc. Finally, by allowing motion at multiple component interfaces, the problems of polyethylene/component wear and limited range of motion are eliminated.

Other objects and features of the present invention will become apparent from the detailed description when studied in connection with the accompanying drawings which disclose several embodiments of the invention. It is to be understood that the drawings are designed for the purpose of illustration only and are not intended as a definition of the limits of the invention. For the purpose of illustration, the present invention is represented as a hip endoprosthesis. However, it is not meant to imply that the present invention is limited to use in the hip. Thus, while several embodiments of the present invention have been shown and described, it will be obvious that many changes and modifications may be made thereunto, without departing from the spirit or scope of the invention.

In the drawings, several reference characters denote similar elements throughout the several views.

FIG. 1 is a frontal view of a joint endoprosthesis embodying the present invention functioning as a hip endoprosthesis. The figure illustrates the orientation of the various components with the lower extremity in the anatomic position (i.e. standing).

FIG. 2 (A and B) consists of two views of the assembled wedge-shaped components illustrating two different orientations. The proximal and distal components are not included to better illustrate the wedge-shaped components.

FIG. 3 is an exploded view of a joint endoprosthesis embodying the present invention illustrating one possible mechanism for its assembly.

FIG. 4 is an exploded view of the component and its relationship to the first wedge-shaped component.

FIG. 5 is an exploded, planar view illustrating one possible swivel mechanism and mode of assembly.

Referring now in detail to the appended drawings, and in particular to FIG. 1 thereof, illustrated is a novel multipolar endoprosthesis embodying the present invention functioning, for the purposes of illustration, as a hip endoprosthesis. The proximal component 12 is firmly affixed to the proximal bony landmark (eg. pelvis) 14 by means of methylmethacrylate bone cement, screws 20, bony ingrowth, etc. in such a way that no motion occurs at the proximal component-bone interface 17. Attached to the proximal component 12 is the first of multiple wedge-shaped components 11 as illustrated in FIGS. 3 and 4. Variation on the assembly technique are possible without departing from the spirit and scope of the invention. The swivel 21, shown in FIG. 1 as a rotatable bearing, is firmly attached to the plane of effacement 19 of a wedge-shaped component 11 via a screw or weld, and is inserted into the swivel receptacle 22 of the proximal component 12 aligning the key 25 with the key hole 26. Aligning the key 25 and the key hole 26 (FIGS. 3 and 4) during insertion of the swivel 21 into the swivel receptacle 22 assures the alignment of the screw tract 23 and screw hole 27. Screwing the set screw 24 through the screw tract 23 and into the screw hole 27 prevents separation or dissociation of the components. Additional wedge-shaped components 11 and the distal component 13 are similarly attached. The distal component 13 is firmly affixed to the distal bony landmark (eg. femur) 15 or into the surgically prepared intramedullary canal 16 by means of methylmethacrylate bone cement, screws, bony ingrowth, etc. in such a way that no motion occurs at the distal component-bone interface 18. While the components 11,12,13 are inseparable except by surgical manipulation, each rotates around axes perpendicular to its planes of effacement 19. Variations on the swivel mechanism are possible without departing from the spirit and scope of the invention.

Passive rotation of one or more of the wedge-shaped components 11 about axes perpendicular to their planes of effacement 19 alters the angular orientation of the wedge-shaped components 11 and, therefore, the proximal component's 12 angular orientation to the distal component 13. This, in turn, alters the angular orientation of the bones 14,15 to which the proximal component 12 and distal component 13 attach. Two different angular orientations are depicted in FIG. 2A and 2B. This illustration is not meant to imply that these are the only two angular orientations that can be assumed.

Thus, while only several embodiments of the present invention have been shown and described, it will be obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.