Differential strain of the axially loaded scapholunate interosseus ligament.

PURPOSE: To directly measure strain changes in the scapholunate ligament via magnetic resonance imaging (MRI) when axially loading the wrist in the neutral and extended positions. METHODS: Six asymptomatic male volunteers without known history of previous wrist injury were enrolled in this MRI-based study. Each subject underwent 3 MRI scans in a 3T scanner: in resting neutral position, in neutral with axial load applied, and in extension with axial load applied. Axial load was applied via extension of an elastic band with known force/elongation curve. We analyzed images and converted them to 3-dimensional stereolithographs. Attachment points of the palmar, proximal, and dorsal sections of the scapholunate interosseus ligament (SLIL) were identified. The lengths of the resulting vectors were recorded for each position. Strain, defined as change in length divided by original length, was calculated for the axially loaded neutral and extended wrists. We used the Bonferroni adjusted multiple comparisons from an analysis of variance model, with statistical significance defined as p < .05. RESULTS: Strains were significantly greater in the palmar (p = .02) and proximal (p = .01) subregions of the SLIL in loaded extension versus loaded neutral positions. In contrast, the strain on the dorsal component in extension was not statistically greater than in the neutral position (p = .45). Axial load in neutral resulted in minimal strain of all 3 components of the SLIL complex, and these were not significantly different from each other (p > .99). With extension, the strains of the palmar (p = .03) and proximal (p = .006) regions were statistically greater than that of the dorsal component. CONCLUSIONS: In extension, strain is greatest in the palmar and proximal portions of the intact SLIL. Axial load in neutral applies minimal strain to the SLIL complex. Avoiding axial loading in extension and encouraging loading in neutral position may allow for decreased injury and more effective healing of the scapholunate ligament.