Morphomechanics of the humero-ulnar joint: I. Joint space width and contact areas as a function of load and flexion angle.

Abstract

Previous studies have shown that the trochlear notch is deeper than necessary for an exact fit with the humerus. However, humero-ulnar joint space width and contact areas have so far not been quantified for variations in the load and angle of flexion. Six fresh cadaveric specimens were investigated at 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion and at loads of 25 and 500 N, simulating resisted elbow extension. The joint space width and contact were determined, using polyether casting material. At 25 N all joints made contact in the ventral and dorsal aspects of the articular surfaces, whereas in the depth of the trochlear notch the joint space was on average between 0.3 and 2.8 mm wide, with some variation between individuals. At 500 N the joint space width was considerably reduced and the contract areas expanded towards the depth of the notch. The size of the dorsal contact areas was significantly smaller at 30 degrees and that of the ventral ones at 120 degrees, their ventro-dorsal ratio decreasing considerably from 30 degrees to 120 degrees (p < 0.01). These results indicate that the size of the contact areas depends to a slight extent on the joint position, but that at all loads and flexion angles a bicentric contact and an important central joint space width emerge because of the concave incongruity of the joint. These data may be used for numerical calculations, analysing the effects of incongruity on the joint stress and on the functional adaptation of the subarticular tissues.