Radiohumeral stability to forced translation: an experimental analysis of the bony constraint.

Radiohumeral stability to forced translation was experimentally analyzed in 8 osteocartilaginous joint preparations. The joints were dislocated in 8 centrifugal directions at 12 different combinations of joint flexion and rotation while a constant joint compression force of 23 N was applied. Stability was measured as the maximum resistance to translation. On average, the specimens could resist a transverse force of 16.4 N (range, 13.0-19.1 N). Stability was greater in some directions than in others. Rotating the joint changed the direction at which stability was greatest, whereas joint flexion did not. In supination, the greatest stability was observed for anteromedial dislocations, in neutral rotation for posteromedial dislocations, and in pronation for posterolateral dislocations. The findings from this study indicate systematic variations in wall height around the radial head concavity as well as individual variations in joint constraint. This may have implications for the treatment of conditions involving radiohumeral joint dislocation.