[Functional anatomy of the fifth carpometacarpal joint]

Apart from the first carpometacarpal joint, the fifth carpometacarpal joint is of importance in gripping and cupping the hand. The present study describes the functional anatomy of the fifth carpometacarpal joint considering morphological and experimental findings. Shape and extension of the cartilaginous articular surface of 50 metacarpal bases show characteristics of a saddle joint. The differences between the dorso-palmar and ulno-radial curvature of the articular surface suggest a main direction of motion in the fifth carpometacarpal joint around an ulno-radial axis. Flexion in this joint ranges from 10 to 15 degrees. After maximal flexion, a supinatory rotation of the metacarpal bone ranging from 10 to 15 degrees is measured. Because of the transverse arched configuration of the carpal bones, the flexion of the fifth metacarpal bone produces opposition towards the thumb. A simultaneous supinatory rotation supports this opposition movement.