Clinical Biomechanics of the Wrist

The wrist enables the human hand to function with precision of motion, power, and stability. The eight carpal bones are anatomically arranged in two rows, with the scaphoid connecting them. The wrist loads through the radial, ulnar and central columns. It maintains stability in all positions with the ligaments that connect carpal rows to form ‘rings.’ Forearm tendons and neuromuscular mechanisms provide dynamic stability. Kinematics of wrist flexion and extension and radioulnar deviation is well described in the literature. The functional wrist motion is the dart thrower’s motion, from radial extension to ulnar flexion. Morphological variations of the scaphoid and the lunate are recognised to affect kinematic patterns of the wrist. Carpal instabilities develop when there is a bony or ligamentous disruption to the ‘carpal rings.’ Instabilities create abnormal kinematic and kinetic patterns leading to degenerative changes. Dynamic CT has been instrumental in understanding these abnormal kinematic and kinetic patterns.