MORPHOMECHANICS OF THE HUMERO-ULNAR JOINT .1. JOINT SPACE WIDTH AND CONTACT AREAS AS A FUNCTION OF LOAD AND FLEXION ANGLE

Background: Previous studies have shown that the trochlear notch is de eper than necessary for an exact fit with the humerus, However, humero -ulnar joint space width and contact areas have so far not been quanti fied for variations in the load and angle of flexion. Methods: Six fre sh cadaveric specimens were investigated at 30 degrees,60 degrees,90 d egrees, and 120 degrees of flexion and at loads of 25 and 500 N, simul ating resisted elbow extension. The joint space width and contact were determined, using polyether casting material, Results: At 25 N all jo ints made contact in the ventral and dorsal aspects of the articular s urfaces, whereas in the depth of the trochlear notch the joint space w as 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 contact areas expanded towards the depth of the notch, The siz e 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). Co nclusion: These results indicate that the size of the contact areas de pends 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. Th ese data may be used for numerical calculations, analysing the effects of incongruity on the joint stress and on the functional adaptation o f the subarticular tissues. (C) 1995 Wiley-Liss, Inc.