RADICAL INSTABILITY OF THE METACARPOPHALANGEAL JOINT OF THE THUMB - ABIOMECHANICAL INVESTIGATION

Human cadaver thumbs were tested to evaluate stability of the radial s ide of the MP joint, The contributions of the dorsal capsule, radial c ollateral ligament, accessory collateral ligament, and volar plate wer e examined with the joint in 0 degrees and 30 degrees of flexion, At 0 degrees flexion, the average joint angulation increased 4 degrees fol lowing isolated radial collateral ligament transection and 6 degrees f ollowing isolated accessory collateral ligament transection, Release o f both the accessory and radial collateral ligaments produced marked i nstability with joint angulation of at least 46 degrees, 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 lab oratory setting, radial-side instability of the MP joint of the thumb requires transection of both the proper and accessory radial collatera l ligaments.