Radial Instability of the Metacarpophalangeal Joint of the Thumb

Abstract

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 collateral ligaments produced marked instability with joint angulation of at least 46° The accessory collateral ligament helped to stabilize the extended MP joint. There were no significant contributions 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.