[Biomechanical investigations on the aetiology of arthrosis of the first carpometacarpal joint (author's transl)].

Forty-eight carpometacarpal joints of the thumb (dissecting room material) were investigated roentgenologically and macroscopically. The localization of arthrotic lesions of the articular surfaces of the first metacarpal bone and the greater multangular bone support the view that arthrosis of the first carpometacarpal joint is due primarly to mechanical factors. The opposition movement of the thumb is combined with a pronating rotation of the first metacarpal bone. This rotation leads to an incongruity of the joint and in consequence to an extreme diminuition of the pressure transmitting area. Photoelastic experiments demonstrate that the point-like contact areas are subjected to an extremly high stress. The functional analysis of the tangential fiber layer in the articular cartilage shows that the first carpometacarpal joint is adapted only to movements typical for a saddle-shaped joint.