To clarify the pathogenesis of osteoarthritis in the trapeziometacarpal (TM) joint, the correlation of the location of osteoarthritic changes with the contact area of the joint was investigated in 102 TM joints from 51 anatomical cadavers. The location of the osteoarthritic changes was studied macroscopically and its severity was classified according to the modified North's classification. The location and area of the articular contact were determined by using the casting method in various positions of the thumb, and the ratio of the contact area to the total joint area was also calculated. Degenerative change was observed frequently in the radial, volar and ulnar segments of the trapezium and in the ulnar segment of the metacarpal bone. When the thumb was held in opposition, the contact area of the trapezium was located in the radial, volar and ulnar segments, corresponding to the place where degeneration of the cartilage frequently occurred. The contact area was the largest with the thumb in opposition. These findings suggested that the TM joint was most stable in opposition where transmission of compressive force was higher than in the other positions. This study revealed that trapeziometacarpal arthritis may be the result of compression forces across the joint with the thumb in opposition.