The effects of partial and total interosseous membrane transection on load-sharing in the cadaver forearm

This study was performed to examine the effects of partial and total transe ction of the interosseous membrane (TOM) on load transfer in the forearm. T wenty fresh frozen forearms were instrumented with custom designed load cel ls placed in the proximal radius and distal ulna. Simultaneous measurements of load cell forces, radial head displacement relative to the capitellum, and local tension within the central band of the IOM were made as the wrist was loaded to 134 N with the forearm at 90 degrees of elbow flexion and in neutral pronation supination. For valgus elbow alignment (radial head cont acting the capitellum), mean force carried by the distal ulna was 7.1 % of the applied wrist force and mean force transferred from radius to ulna thro ugh the IOM was 4.4%. For varus elbow alignment (mean 2.0 mm gap between th e radial head and capitellum), mean distal ulna force was 28% and mean TOM force was 51%. Section of the proximal and distal one-thirds of the IOM had no significant effect upon mean distal ulnar force or mean IOM force. Tota l IOM section significantly increased mean distal ulnar force for varus elb ow alignment in all wrist positions tested. The mean level of applied wrist force necessary to close the varus gap (89 N) decreased significantly afte r both partial TOM section (71 N) and total IOM section (25 N). The IOM bec ame loaded only when the radius displaced proximally relative to the ulna, closing the gap between the radius and capitellum. As the radius displaced proximally, the wrist becomes increasingly ulnar positive, which in turn le ads to direct loading of the distal ulna. This shift of force to the distal ulna could present clinically as ulnar sided wrist pain or as ulnar impact ion after IOM injury. (C) 2001 Orthopaedic Research Society. Published by E lsevier Science Ltd. All rights reserved.