IE41668B1 - Prosthetic bone joint devices - Google Patents

Abstract

1526941 Elbow joints G R BREMBLE and K HARDINGE 3 Sept 1975 [4 Sept 1974] 38749/74 Heading A5R [Also in Division E2] An endoprosthetic elbow joint comprises a humeral component 10, Fig. 2, and an ulnar component 20, Fig. 6, each of generally part and hollow-right-circular cylindrical form and having substantially complementary convex, 11, and concave 21, bearing surfaces for mutual articulatory engagement, and concave, 12, and convex, 22, fixation surfaces of relieved configuration. The humeral component fixation surface 12 has raised rectangular areas 13, the component 10 being of metal e.g. stainless steel and being of semicircular circumferential extent. The extent of the ulnar component 20 is 40‹-45‹, the fixation surface 22 including raised rectangular areas 23, being longer than surface 21 and joined thereto by chamfered surfaces 24, the component 20 being of plastics e.g. ultra high molecular weight polyethylene, and radially thicker than the component 10. The components are applicable to left or right elbows.

Description

This invention concerns prosthetic bone joint devices and relates particularly to endoprosthetic elbow joint devices.

The forms of the latter devices in current usage normally involve a directly-linked mechanical hinge of all metal construction which is secured to the humerus and ulna by way of intramedullary stems. While such hinged devices have proved satisfactory in the shorter term, it is now thought that they are subject to disadvantage in the longer term. More specifically, there is a tendency for the securement of the device to be weakened by transmission of stresses through the device itself and there is, in any case, disadvantage in the relatively large removal of bone and deep medullary penetration which is required for such hinged devices.

An object of the present invention is to reduce these disadvantages and, to this end, there is provided, according to one aspect of the invention, an endoprosthetic elbow joint device comprising a humeral component and an ulnar component each of generally part-hollow-cylindrical form, respectively having substantially complementary convex and concave right circular cylindrical bearing surfaces for mutual articulatory engagement, and respectively having concave and convex fixation surfaces provided with relieved configurations for securement by cement to the humerus and ulna.

Preferably, the humeral component bearing surface has a circumferential angular extent of about 180°, while the . ο corresponding extent of the ulnar component is about 40 , thus allowing a range of articulation of the latter surface on the former similar to that in the natural joint, namely, about 140°.

Also, it is presently preferred that the two components be of respectively integral metal and plastics material such as used in other bone joint prostheses, and that the metal humeral component be markedly thinner than the plastics ulnar component.

For a clearer understanding of these and other features, the same will now be described as embodied in a prototype device according to the invention, the prototype being illustrated in the accompanying drawings, in which:Figures 1 to 4 respectively illustrate the humeral component of the device in end, side, transverse medial section taken at I - I, and plan views, and Figures 5 to 8 similarly illustrate the associated ulnar device, the section being taken at II - II.

The illustrated humeral component is denoted generally at 10 and is basically in the form of a part-hollow-right-circular, cylindrical body of semi-circular circumferential extent. The convexly curved surface 11 of this body serves as a bearing surface, and the concavely curved surface 12 serves as a fixation surface but is formed with a relieved configuration comprising an array of mutually-spaced, raised rectangular areas 13 of low height relative to their lateral dimensions.

The humeral component 10 is of integral metal construction, suitably of stainless steel of appropriate quality for the present purpose.

The illustrated ulnar component is denoted generally at 20 and is also basically in the form of a part-hollow-right-circular cylindrical body. The concavely curved surface 21 of this body serves as a bearing surface for articulatory engagement with the humeral component bearing surface 11 and accordingly has the same radius of curvature. Also, as noted earlier, the surface 21 is of lesser circumferential angular extent than surface 11, and is suitably of 40°-45° extent. The convexly curved surface 22 of the body 20 serves as a fixation surface and is formed with a relieved configuration comprising an array of mutually-spaced raised rectangular areas 23 having low height relative to their lateral dimensions similarly to the humeral component fixation surface 12. Also the surface 22 is of lesser circumferential extent than surface 12, but greater than surface 21, surfaces 21 and 22 being joined by respective chamfered end surfaces 24 defined by chordal planes which are parallel to the cylindrical axis of the body 20 and mutually convergent radially outwardly from this axis as seen in Figure 6. Further features of the ulnar component are seen to comprise rounding of the circumferential ends of the body adjacent the bearing surface by longitudinal convex curving as seen in both plan and end views.

The ulnar component 20 is of integral plastics material construction, suitably from ultra high molecular weight polyethylene and is markedly radially thicker than the humeral component.

In use of the illustrated embodiment the head of the radius is excised; bone is removed from the humerus in the region of the trochlea to receive the humeral component as a capping therearound with its fixation surface innermost for securement with acrylic cement keyed between the exposed cancellous bone and relieved surface configuration of the component; and bone is removed from the cororioid and olecranon to receive the ulnar component sealed in tho latter as a socket with its fixation surface innermost for cement securement in similar manner to the humeral component.

Such location of the components allows mutual articulatory engagement of their bearing surfaces affording similar movement to that of the natural joint.

The capping of the humerus by the humeral component is facilitated by use of metal construction which allows use of a thin component and therefore requires little removal of bone, while at the same time this is the more extensive component and secure fixation is possible. The ulnar component, is contrast, is thicker and less extensive, but this is compatible with the potentially greater rate of wear of plastics material and seating of the component within the ulna. In this last connection, it will he appreciated that the rounding of the ulnar component ends allows the same to be seated in the ulna while conforming generally to the contours of the remanant adjacent bone. A further functional feature of the ulnar component is that the mutually convergent end surfaces 24 act against dislocation, it being understood that the components are not directly mechanically linked but are held in engagement by the muscular and ligamentous elements of the natural joint.

It is to be noted that the illustrated components are symmetrical in so far as they are applicable to left and right elbows.

Clinical trial experience to date with devices of the illustrated form indicate that the device form is generally satisfactory. However, modification may be preferred to facilitate accurate relative location of the two components during inplantation.

For this last purpose it is proposed that the components be provided with one or more short stems or studs projecting from their fixation surfaces to a greater extent than the areas 13, 23, each for receipt in a'suitably located hole in the respective bone. Conveniently this modification can be effected by extending one or more of the areas 13 and 23 to project further than shown in the drawings.

Claims (8)

1. Ah endoprosthetic ellpow joint device comprising a humeral component and an ulnar component each of generally part-hollowcylindrical form, respectively having substantially complementary convex and concave right circular cylindrical bearing surfaces for mutual articulatory engagement, and respectively having concave and convex fixation surfaces provided with relieved configurations for securement by cement to the humerus and ulna.

2. A device according to Claim 1 wherein said humeral component bearing surface has a circumferential angular extent of about 180° and the corresponding extent of said ulnar component bearing surface is about 40°.

3. · A device according to Claim 1 or 2 wherein said components each comprise a main body portion of part-hollow-right circular cylindrical form having one surface relieved to define a plurality of upstanding areas of low height relative to their lateral dimensions, said one relieved surface being the respective fixation surface.

4. A device according to Claim 3 wherein the main body portion of said ulnar component has chamfered circumferential end faces which are mutually convergent in a radially outward direction from the associated cylindrical axis towards such portion.

5. - A device according to Claim 3 or 4 wherein the main body portion of said ulnar component has circumferential ends which are longitudinally convexly curved.

6. A device according to Claim 3i 4 or 5 wherein at least one of said components is provided with a stud or stem projecting from its fixation Surface to a greater extent than the respective ones of said upstanding areas. 5

7. - A device according to any preceding claim wherein said humeral component is substantially thinner than said ulnar component, and said components are of integral, respectively metal and plasties material, construction.

8. An endoprosthetic elbow joint device substantially as herein 10 described with reference to the accompanying drawings.