Variation in the position of the elbow flexion axis after total joint replacement with three different prostheses.

The instantaneous flexion axes in rheumatoid patients treated with a Kudo (Biomet UK Ltd, Swindon, UK), Capitellocondylar (Johnson & Johnson Orthopaedics Inc, Raynham, MA), or GSB III (Zimmer GmbH, Winterthur, Switzerland) elbow prosthesis were calculated using radiostereometric analysis and compared with those previously found in the normal elbow in vivo. Variability in the flexion axis position was greater in the prosthetic elbows than reported for healthy subjects. This was especially evident for the unlinked Kudo prosthesis, with dispersions of the axes up to 84.3 degrees in the frontal and 45.0 degrees in the horizontal plane. Corresponding values for the unlinked Capitellocondylar prosthesis were 19.7 degrees and 20.9 degrees. The linked GSB III prosthesis was the most constrained, with dispersions within 15.4 degrees in the frontal and 4.6 degrees in the horizontal plane. The unlinked elbow prostheses displayed considerable axis dispersion under physiologic conditions. Implant design seems to be able to compensate for this to some extent, as indicated, for example, by the results of the Capitellocondylar prosthesis.