Joint stability after total shoulder arthroplasty in a cadaver model.

A cadaver model was used to test the hypothesis that glenohumeral joint stability is independent of articular surface conformity after total shoulder arthroplasty. For the purposes of this study joint stability was defined as the minimum force required for joint dislocation. After arthroplasty components were implanted into fresh-frozen glenohumeral joints, specimens were mounted on a load frame and tested for joint stability. For each specimen the amount of conformity between the articular surfaces was varied from 0 to 5 mm by changing the humeral head radius of curvature. Because the glenoid component was not charged, the wall height, or joint constraint, was maintained constant for a given specimen. Variations in joint conformity changed dislocation forces by an average of only 3%. These small differences are not believed to be clinically relevant, indicating that design changes affecting the joint conformity of a total shoulder arthroplasty system will not significantly affect glenohumeral joint stability, assuming that all other factors remain constant.