ABSTRACT
PURPOSE: Carpal bones show hysteresis that is dependent on the direction of wrist motion during a continuous active loading protocol. We describe an accurate methodology for analyzing the hysteresis effect and we apply this model to analyze the effect of sequential ligament sectioning on scapholunate instability. METHODS: In 8 fresh cadaver forearms scaphoid, lunate, and third metacarpal motions were recorded while each wrist was moved in continuous cycles of active motion in flexion-extension and radioulnar deviation. Motions were analyzed for the intact state and after sequential sectioning of the scapholunate interosseous, scaphotrapezium, and radioscaphocapitate ligaments. Carpal motion was curve-fitted with respect to the third metacarpal motion using optimization criteria. The area between the 2 curves that represents opposite directions of wrist motion was measured to give the total hysteresis area. Repeated-measures analysis of variance was used to determine significance. RESULTS: In the flexion-extension trials the scaphoid and lunate total hysteresis area was significantly greater than the intact state only after all 3 ligaments were sectioned. In the radioulnar deviation trials the scaphoid total hysteresis area was significantly greater than the intact after just scapholunate interosseous ligament sectioning; however, the lunate total hysteresis area decreased with additional sequential sectionings in 4 of the 8 specimens as compared with the intact state. These 4 specimens started with a significantly greater intact total hysteresis area than the other 4 specimens. CONCLUSIONS: The computation of the total hysteresis area from the hysteresis effect was found to be a sensitive technique to determine the subtle onset of abnormal carpal motion. By using this technique in a ligament sectioning study significant increases in the total hysteresis area were seen after just scapholunate interosseous ligament sectioning during wrist radioulnar deviation. This subtle change may signify the onset of dynamic scapholunate instability. The total hysteresis area of the lunate in a subset of lax specimens did not increase after ligament sectioning. This divergent behavior may explain why some patients with scapholunate instability do not develop dorsal intercalated segmental instability.