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 stability. Soft tissue restraints were left to provide the primary stabilization of the thumb basal joint complex. Both degenerative and traumatic conditions compromise the function of these ligamentous structures and result in translational instability of the joint surfaces and secondary arthritic disease. Primary idiopathic osteoarthritis, Bennett's fracture-dislocation, and metacarpophalangeal hypermobility all impart a disturbance in biomechanics while extension metacarpal osteotomy, ligament reconstruction, and imposed metacarpophalangeal flexion mitigate these effects and improve trapeziometacarpal kinematics. As a compact joint amenable to en bloc resection, the trapeziometacarpal complex affords a unique opportunity to study the inter-relationship between biology and biomechanics in the pathogenesis of degenerative joint disease.