Flexion and extension of the wrist occurs at the radiocarpal and midcarpal joints. This study examined the angular contribution of the radiocarpal and midcarpal joints to the total arc of motion.

Five healthy adults were selected and ten wrists were tested. Lateral X-rays were taken with the wrist in the neutral position, 30 ° flexion, 60 ° flexion, 90 ° flexion, 30 ° extension, 60 ° extension, and 90 ° extension. The radiocarpal and midcarpal angle were measured. The angular contribution of the radiocarpal and midcarpal angle was calculated at each phase of motion; neutral to 30 °, 30 ° to 60 °, 60 ° to 90 °.

During wrist flexion, the angular contribution of the midcarpal joint was 65%, 72%, 71% at each phase of motion, respectively. During wrist extension, the angular contribution of midcarpal joint was 37%, 53%, 78% at each phase of motion, respectively. Therefore, during wrist extension, the main contributor of motion is changed from the radiocarpal joint in the early phase to the midcarpal joint in the late phase.

It is suggested that the proximal carpal low is not moved passively by just the link system but the motion is guided by the peculiar shape of midcarpal articulation and ligaments complex at each phase. The link system is believed to act in the early phase of flexion and in late phase of extension.