RADIAL INSTABIL ITY OF THE METACARPOPHALANGEAL JO INT OF THE THUMB A b iomeehan iea l invest igat ion

Human cadaver thumbs were tested to evaluate stability of the radial side of the MP joint. The contributions of the dorsal capsule, radial collateral ligament, accessory collateral ligament, and volar plate were examined with the joint in 0 ° and 30 ° of flexion. At 0 ° flexion, the average joint angulation increased 4 ° following isolated radial collateral ligament transection and 6 ° following isolated accessory collateral ligament transection. Release of both the accessory and radial col-lateral ligaments produced marked instability with joint angulation of at least 46 °. The accessory collateral ligament helped to stabilize the xtended MP joint. There were no significant contri-butions to stability from the dorsal capsule and volar plate when the collateral ligaments were intact. In the laboratory setting, radial-side instability of the MP joint of the thumb requires transection of both the proper and accessory radial collateral ligaments. Journal of Hand Surgery (British and European Volume, 1995) 20B: 1. " 102-104 Radial collateral ligament injuries have been reported to occur with as high as 64 % of the frequency of ulnar collateral ligament injuries (Camp et al, 1980; Coonrad and Goldner, 1968; Frank and Dobyns, 1972; Gano