The effect of partial removal of proximal ulna on elbow constraint.

Accepted clinical practice allows the resection of up to 80% of the olecranon in comminuted fractures. Although this procedure is well-established, its effect on the static stability of the ulnohumeral joint has not been studied. An experiment was designed to study the amount of the greater sigmoid fossa of the ulna that can be removed before significant static ulnohumeral instability may occur. In eight fresh specimens, tested both in extension and at 90 degrees of flexion, changes in constraint were studied in four displacement, two torsional, and two axial modes. The constraint of the ulnohumeral joint appeared linearly proportional to the area of remaining articulation and was not provided solely by the distal 25%. The proximal portion of the olecranon has a greater effect on joint constraint than is generally appreciated.