The distribution of motion between the radiocarpal and midcarpal joints in scapholunate instability is poorly understood. This has potential implications in predicting degenerative changes and in selecting salvage procedures. We studied 19 healthy wrists and 19 wrists with scapholunate instability using dynamic computed tomography during wrist extension to flexion and ulnar to radial deviation. Radiocarpal and midcarpal kinematics of the scaphoid and the lunate were computed. In scapholunate instability, in the radial column, there was increased motion in the radiocarpal joint when the wrist was radially deviating beyond 10° or moving from 70° to 40° extension. In both groups, the capitolunate joint was the dominant articulation in the central column. In scapholunate instability, there was significantly more capitolunate motion during 70° to 30° extension. These changes may predict the development of radioscaphoid arthritis and enable identifying a kinematically abnormal wrist. The motion distribution in scapholunate instability was abnormal beyond 10° of radial deviation and between 70° and 40° of wrist extension.Level of evidence: III.
Keywords: Midcarpal kinematics; carpal instability; dynamic computed tomography; in vivo kinematics; radiocarpal; scapholunate.