Osteoarthritis of the trapeziometacarpal joint: the pathophysiology of articular cartilage degeneration. I. Anatomy and pathology of the aging joint.

An anatomic study of the trapeziometacarpal joint was conducted on 47 cadaver thumb specimens. The superficial capsule restrained only metacarpal rotation about its long axis. Intracapsular anatomy was notable for a large anterior subthenar recess limited dorsally by the abductor pollicis longus insertion and palmarly by the deep palmar or "beak" ligament. This beak ligament was essential for translational stability of the metacarpal on the trapezium with flexion of the thumb ray. There was a direct correlation between the status of the articular surfaces and the integrity of the beak ligament. Normal surfaces were associated with an intact ligament confluent with the hyaline cartilage of the palmar lip of the metacarpal; degeneration of the palmar lip cartilage was always associated with attritional detachment of the beak ligament. Advanced articular disease occurred only in the palmar contact areas and was predicted by degeneration of the adjacent beak ligament; only nonprogressive chondromalacia was found on the dorsal portions of the articular surfaces.