US 3919725 A
An endoprosthetic elbow joint device of hingeless form comprises humeral and ulnar components which are each of trough form. The humeral component outer surface is of circular cylindrical form over at least part of its length and is secured to the humerus at its inner surface, while the ulnar component has a complementary circular cylindrical inner surface for mutually articulatory bearing engagement with the humeral component and is secured to the ulna at its outer surface. In a modification the humeral component has a convex, part-annular, part-spherically shaped extension to its outer surface, which extension articulates with a complementary concave surface of an additional component for securement to the radius.
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United States Patent [191 Swanson et al.
[ ENDOPROSTHETIC ELBOW JOINT DEVICES  Inventors: Sydney Alan Vasey Swanson,
Carshalton; Brian Arnold Roper, London, both of England  Assignee: National Research Development Corporation, London, England  Filed: Nov. 30, 1973  Appl. No.: 420,578
 Foreign Application Priority Data Nov. 30, 1972 United Kingdom 55350/72  US. Cl. 3/191; 128/92 C  Int. Cl. A61F 1/24  Field of Search 3/1, 1.9-1.912; 128/92 C, 92 CA, 92 R  References Cited UNITED STATES PATENTS 3,506,982 4/1970 Steffee 128/92 C X 3,521,302 7/1970 Miiller 3/1 Nov. 18, 1975 Stevens 128/92 C Averill et a1. 3/1
 ABSTRACT An endoprosthetic elbow joint device of hingeless form comprises humeral and ulnar components which are each of trough form. The humeral component outer surface is of circular cylindrical form over at least part of its length and is secured to the humerus at its inner surface, while the ulnar component has a complementary circular cylindrical inner surface for mutually articulatory bearing engagement with the humeral component and is secured to the ulna at its outer surface. In a modification the humeral component has a convex, part-annular, part-spherically shaped extension to its outer surface, which extension articulates with, a complementary concave surface of an additional component for securement to the radius.
9 Claims, 9 Drawing Figures US Patent .Nov. 18, 1975 3,919,725
1 ENDOPROSTI-IETIC ELBOW JOINT DEVICES This invention concerns prosthetic 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 allmetal 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. 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, provides an endoprosthetic elbow joint device, which, in a more general aspect, comprises: a humeral component in the form of a cap having a generally U-shaped channel cross-section relative to a longitudinal axis therethrough, with an outer bearing surface of circular arcuatecross-seCtion centered on said axis, and an inner fixation surface encompassing said axis; and an ulnar component in the form of a socket hving an inner bearing surface of substantially complementary shaping to at least a longitudinal position of said outer bearing surface to receive the same in mutually articulatory engagement, and an outer fixation surface, said inner and outer fixation surfaces being adapted for respective securement to the humerus and ulna.
The proposed device can take a first form which, in common with the conventional hinged form of device, involves excision of the distal head of the radius. In this first form the humeral component bearingsurface is preferably substantially circular cylindrical.
In a second form of the proposed device provision is made for replacement of the radial articulation in the elbow joint function by augmenting the humeral component and by the addition of a radial component. In this case the humeral component is basically as defined above with'a first portion of said outer bearing surface being complementary with said ulnar component bearing surface, and a second portion of said outer bearing surface being of convex, substantially part-spherical shaping, located adjacent one end of said first portion, centred on said axis, and having greater radius than said first portion. This second portion engages a radial component having a complementary concave bearing surface and a fixation surface.
Whatever the form of the proposed device, it is presently preferred that the humeral component be thinwalled relative to the ulnar component, and that these components be made respectively of metal and plastics material. The radial component is also preferably of plastics material in these circumstances.
Regarding the fixation surfaces of the components: these will normally be intended to facilitate securement to the relevant bones with use of acrylic cement or equivalent gap-filling medium, but without use of long intramedullary stems. For this purpose the fixation surfaces comprise relieved formations, such as grooves,
ribs or studs, which are preferably of shallow depth relative to the dimensions of the respective bearing surfaces, although such formations may in some circumstances be replaced or augmented by stems having lengths not significantly greater than said dimensions.
, side views,
FIGS. 3, 4 and 5 illustrate the associated ulnar component of this embodiment in respective end, side, and plan views,
FIG. 6 diagrammatically illustrates in a sectional view the positioning of the first embodiment relative to the humerus and ulna,
FIGS. 7 and 8 illustrate the humeral component of a second embodiment of the invention in respective end and side views, and
FIG. 9 illustrates the associated radial component of this second embodiment in side view.
The humeral component of FIGS. 1 and 2 is a cap for the lower end of the humerus, the cap'being denoted at 1 in the form of a cylindrical open-ended through, having an outer bearing surface 2 of major segmental circular arcuate cross-sectional shape centred on'a longitudinal axis 3 of the trough, and an inner fixation surface 4. encompassing the axis 3. The inner surface 4 has, as seen in FIG. 1, a cross-sectional shaping formed by a parallel-sided slot terminating in a semi-circular base centred on the axis 3, this slot being in symmetrical relation with the outer bearing surface 2. The inner surface 4 does not have, a relieved formation, but such a formation may be appropriate by the provision of slots or in equivalent manner.
The associated ulnar component of FIGS. '3 to 5 is a socket for the upper end of the ulna, the socket being denoted at 6-in the general form of an open-ended through having an inner bearing surface 7 of minor-segmental circular arcuate cross-sectional shape and like radius as the outer bearing'surface 2 of the humeral component to receive the same in mutual articulatory bearing engagement. The longitudinal end portions of the side walls of the socket are smoothly downwardly tapered with convex circular quadrant profiles 8 which are of equal radius in the present instance, but may differ in other embodiments. The remaining outer surface 9 of the socket is of generally tapered or frusto-pyramidal form converging remotely from the inner bearing surface 7. Also, the outer surface 9 has a relieved formation which in this instance is provided by at least one V-shaped slot 10 extending across the underneath of the trough as shown in FIG. 4.
In a modified form of this ulna component, the relieved formation is augmented by the provision of a short stub 12 as shown in broken outline in FIGS. 3 and 5.
The components of the embodiment just described are made of materials according to the above-indicated preference, with the humeral component being made of a metal such as a chrome-cobalt alloy or stainless steel, and the ulnar component being made of a plastics material such as high density polyethylene.
The positioning of the components relative to the associated bones is diagrammatically illustrated by FIG. 6. The capitulum 21 of the humerus 22 is retained, while the trochlea 23 of the humerus is cut down to fit the channel cavity of the cap 1 into which it is secured with acrylic resin. The head of the radius is excised, and
the ulnar 24 is recessed to receive the socket 6 for securement with acrylic cement.
An additional point to note is that the natural shape of the trochlea forms a neck behind the cap 1. This neck serves to facilitate flexion and extension between the bones in the natural joint and serves a similar function in the prosthesis. The tapered shaping 8 of the end portions of the socket side walls also contributes to this function, these portions being such as to correspond approximately to those parts of the coronoid and olecranon processes which are replaced thereby. More particularly, the side wall end portions replacing the part of the olecranon process closest to the articular surface can then pass into the olecranon fossa of the humerus to allow the device to move towards a position of full extension in the natural joint.
In the second illustrated embodiment the humeral component is again in the form of an open-ended trough denoted at 31 of which a first portion is a duplication of FIGS. 1 and 2 with bearing surface 2, longitudinal axis 3, and fixation surface 4. This first portion is augmented at one end by a second portion comprising a convex, part-annular, spherical bearing surface 32 centred on the axis 3, the spherical shaping of this surface being of greater radius than the surface 2, but the circumferential extent of the part-annular shaping around the axis 3 is the same as that of the surface 2. The component is intended to be integral in this instance and the surfaces 2 and 32 are separated by a groove to facilitate their formation. However, the component can be formed in separate first and second portions connectable in any suitable manner to dispose the surfaces 2 and 32 in the illustrated relative positions in predetermined manner. In either event, the fixation surface 4 continues behind the surface 32.
The associated radial component of FIG. 9 is denoted at 41 and comprises a disc member 42, having a concave part-spherical bearing surface 43 in one face thereof, while the other face thereof defines the respective fixation surface and has a short stem 44 projecting therefrom. The bearing surface 43 is complementary with the second portion bearing surface 32 of the associated humeral component.
The humeral and radial components just described are intended to be used with an ulnar component such as that illustrated in FIGS. 3 to 5, and implantation is basically as with the first embodiment except that the preparation of the humerus is extended to receive the longer humeral component 31, and the distal end of the radius is not excised but is prepared to receive the radial component 41. In any event, implantation is effected whereby the humeral component first and second portion bearing surfaces 2 and 22 are in respective mutual articulatory engagement with the bearing surfaces 7 and 43 of the ulnar and radial components.
The advantages of these devices according to the invention can be appreciated by comparison with the currently conventional form of endoprosthetic elbow joint devices. As noted initially above, the latter devices are normally of all-metal construction, mechanical hinge form, involving intramedullary stem fixation in both the humerus and ulna. The present devices are of simpler and more compact geometry which fits within the capsule of the natural joint to be held in bearing relation thereby without the use of a mechanical hinge structure. The absence of long intramedullary stems in the present devices contributes significantly to their compactness and correspondingly reduces the need for removal and excavation of bone. Further-- more, the absence of long intramedullary stems reduces the dangers associated with any infection which may occur and simplifies the total removal of infected material if this becomes necessary. Similarly, the absence of a mechanically-linked hinge structure simplifies the implantation procedure and, perhaps more important, simplifies removal of the device in the event that this becomes necessary. Also, the absence of a mechanically-linked hinge limits the forces which can be transmitted through the prosthesis and thereby reduces the probability of loosening of the components.
The absence of long intramedullary stems and a mechanically linked hinged structure is further advantageous in respect of manufacture. intramedullary stems often involve the provision of oppositely handed components for left and right and joint, and linked structures commonly involve the production of at least three components for each device. These requirements can be redundant with the present invention.
There is also advantage in the preferred choice and application of materials to the present device. Metal/- plastics material combinations are favored for other endoprosthetic bone joint devices for their low friction bearing properties, and this is taken into account in the present device. Moreover, the preferred allocation of materials to the components allows the use of bearing surfaces of relatively large radius which spreads the bearing load over a greater area and acts against dislocation, while the metal cap component can be of thinner walled form to reduce the requirement for bone removal, and the plastics material of the socket component or components, which material is more susceptible to wear, is also the thicker walledcomponent.
1. A total endoprosthetic elbow joint device, comprising:
a humeral component in the form of a cap having a symmetrical open-ended, entirely U-shaped channel relative to a longitudinal axis therethrough, said humeral component defining an outer bearing surface of circular arcuate cross section centered on said axis, and defining an inner fixation surface forming a slot encompassing said axis; and
an ulnar component in the fonn of a socket having an open-ended generally U-shaped channel relative to said axis, said ulnar component defining an inner bearing surface substantially complementary to and engaged with at least a longitudinal portion of said outer bearing surface of said humeral component for mutual articulation about said axis between said bearing surfaces, and defining an outer fixation surface, said inner bearing surface and the bordering parts of said outer fixation surface being convergently tapered towards each of the longitudinal ends of said ulnar component, said fixation surfaces being adapted to be secured relative to respective bone ends by a cementitious gap filling medium.
2. A device according to claim 1 wherein said inner fixation surface is in the form of a longitudinal slot having a cross-sectional shape with parallel sides joined by a semi-circle, which shape is symmetrically located relative to said outer bearing surface and being inwardly non-diverging in cross section.
3. A device according to claim 1 wherein said tapering follows convex, circular arcuate shaping.
4. A device according to claim 1 wherein said outer fixation surface is of generally wholly tapered form converging remotely from said inner bearing surface.
5. A device according to claim 4 wherein said outer fixation surface tapering is of generally frusto-pyramidal form.
6. A device according to claim 1 wherein said outer bearing surface comprises a further portion of convex, substantially part-spherical shaping, located adjacent one end of the first-mentioned portion, centred on said axis, and having greater radius than said first portion; and said device further comprises a radial component having a bearing surface having a concave shaping complementary to and engaged with said convex surface for mutual articulation therebetween; and a fixation surface adapted for securement with the radius.
7. An endoprosthetic elbow joint device comprising:
a humeral component in the form of a cap having an open-ended, generally U-shaped channel relative to a longitudinal axis therethrough, said humeral component defining and outer bearing surface with a part-circular-cylindrical first longitudinal portion and a part-spherical second longitudinal portion of greater radius than said first portion, and defining an inner fixation surface forming a slot encompassing said axis;
an ulnar component in the form of a socket having an open-ended generally U-shaped channel shape relative to said axis, said ulnar component defining a partcircular-cylindrical inner bearing surface complementary to and engaged with said outer bearing surface of said first portion; and
a radial component defining a bearing surface which is concave relative to, and engaged with, said outer bearing surface of said second portion.
8. A total endoprosthetic elbow joint device comprising:
a humeral component having a first symmetrical, entirely U-shaped channel form relative to a longitudinal axis therethrough, which form defines a longitudinal outer surface of convex circular cylindrical shape centered on said axis, and a longitudinal inner surface of open-ended shape encompassing said axis, said convex cylindrical shape having major circular segmental extent in cross section; and
an ulnar component of generally U-shaped channel form, which form defines a longitudinal inner surface of concave circular cylindrical shape complementary to and engaged with said convex cylindrical shape of said humeral component for mutual articulation about said axis, and a generally convex outer surface, said concave cylindrical shape having minor circular segmental extent in cross section, and the longitudinal ends of said concave cylindrical shape and adjacent parts of said convex outer surface being convergently tapered, said fixation surfaces being adapted to be secured relative to respective bone ends by a cementitious gap filling medium.
9. A total endoprosthetic elbow joint device, comprising:
a humeral component having a first entirely U- shaped channel form relative to a longitudinal axis therethrough, said first form defining a longitudinal outer bearing surface and a longitudinal inner fixation surface, said outer bearing surface having a symmetrical longitudinal shape and a convex circularly arcuate cross-sectional shape which is centered on said axis and of greater arcuate extent than a semi-circle, said inner fixation surface having an open-ended symmetrical shape and a symmetrical concave inwardly non-diverging cross-sectional shape, and said outer bearing surface and said inner fixation surface being mutually symmetrically located; and
an ulnar component of a second U-shaped channel form defining a longitudinal inner bearing surface and a longitudinal outer fixation surface, said inner bearing surface being complementary to and engaged with said outer bearing surface for mutual articulation about said axis, said inner bearing surface having circularly arcuate cross-sectional shape of lesser arcuate extent than a semi-circle, and the longitudinal ends of said inner bearing surface and bordering parts of said outer fixation surface being convergently tapered, said fixation surfaces being adapted to be secured relative to respective bone ends by a cementitious gap filling medium.
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