Pathomechanics of the thumb trapeziometacarpal joint

As the human thumb climbed the evolutionary ladder, the trapeziometacarpal joint was provided greater mobility at the expense of decreased bony stabil ity. Soft tissue restraints were left to provide the primary stabilization of the thumb basal joint complex. Both degenerative and traumatic condition s compromise the function of these ligamentous structures and result in tra nslational instability of the joint surfaces and secondary arthritic diseas e. Primary idiopathic osteoarthritis, Bennett's fracture-dislocation, and m etacarpophalangeal hypermobility all impart a disturbance in biomechanics w hile extension metacarpal osteotomy, ligament reconstruction, and imposed m etacarpophalangeal flexion mitigate these effects and improve trapeziometac arpal kinematics. As a compact joint amenable to en bloc resection, the tra peziometacarpal complex affords a Unique opportunity to study the inter-rel ationship between biology and biomechanics in the pathogenesis of degenerat ive joint disease.