To investigate the changes in length of the scapholunate interosseous ligament (SLIL) when the wrist is resisting horizontal lateral load and the forearm is in full pronation in vivo.
We obtained computed tomography scans of the wrists of 6 volunteers in 3 situations: 0° position (0° extension and 0° ulnar inclination) and full forearm pronation without force, and in the same position but with resisted ulnar and radial deviation. Nine zones of 3 subregions of the SLIL were measured and analyzed with computer modeling.
Changes in length of the palmar SLIL with resisted ulnar deviation were significantly greater than those without an applied lateral load. In contrast, the changes in length of the dorsal SLIL with resisted radial deviation were statistically greater than those in the 0° position without loading. However, no significant differences in the changes in length of the proximal SLIL were found in any of 3 situations, except the dorsal zone with resisted radial deviation.
Application of lateral load has an effect on the separation of the palmar and dorsal insertions of the SLIL. The palmar subregion of the SLIL was more highly strained with wrist-resisted ulnar deviation. Conversely, the dorsal subregion of the SLIL was under greater tension with wrist-resisted radial deviation.
For patients undergoing nonsurgical treatment of SLIL tears, a sudden contraction of ulnar or radial deviation agonist muscles may be harmful and contribute to SL instability.