This in vivo carpal kinematic study utilized a motion analysis system based on CT scans of 14 male and 14 female subjects evaluating a total of 504 wrist positions distributed within the range of positions of approximately 60 degrees of flexion to 70 degrees of extension and from 30 degrees of radial deviation to 40 degrees of ulnar deviation. The investigators confirmed that the scaphoid and the lunate primarily flex or extend in all directions of wrist motion. However, scaphoid and lunate rotations approach zero at wrist positions along the dart thrower’s path which occurred about a line that passed from radial extension to ulnar flexion. That is, the scaphoid and lunate extended at wrist positions above this path and flexed at wrist positions below this path despite the fact that these positions included combinations of wrist flexion and extension as well as radial and ulnar deviation. Slight radial translation was noted during extension of the scaphoid and lunate, but little translation was noted during flexion. There were no significant gender differences noted other than a more proximal rotation axis in female subjects which may be related to the diminished carpal size.
This study confirms a critical direction of wrist motion, which may be evolutionary, whereby proximal carpal row motion is minimized along a dart thrower’s motion. Along this path, a transition is defined between flexion and extension rotation of the scaphoid and lunate at which their motion approaches zero. This path confers a unique degree of radiocarpal stability and may be considered the primary functional direction of the radiocarpal joint. Therapeutic protocols may be considered along the dart thrower’s motion to limit, for example, scapholunate rotation motion during interosseous ligament healing while allowing for early mid-carpal motion. Future biomechanic studies should make use of this axis to further our knowledge related to other pathologies related to the carpus.
Dart, Throwers, Carpal, Motion, Wrist, Kinematics
Journal of Bone and Joint Surgery