The interosseous membrane and its influence on the distal radioulnar joint. An anatomical investigation of the distal tract.

From the interosseous membrane of the forearm a tract extends to the dorsal capsule of the distal radioulnar joint. The structure and function of this tract have been investigated. The tract originates from the radius 22 mm proximal to the distal dorsal corner of the sigmoid notch. Central fibres are attached there with fibrous cartilage and superficial bundles mix with the periosteum. The tract is 8 mm wide, 31 mm long and 1 mm thick. Distally it inserts at the capsule of the distal radioulnar joint between the tendon sheaths of extensor digiti minimi and extensor carpi ulnaris. Deep fibres insert directly at the triangular fibrocartilage. The tract of the interosseous membrane is taut in pronation and loose in supination. It strengthens the dorsal capsule of the distal radioulnar joint. During pronation the tract protects the ulnar head in a sling. Its attachment at the triangular fibrocartilage influences the distal radioulnar joint. Its insertion at the triangular fibrocartilage and the support of the weakest part of the dorsal capsule are of interest.