Normal Contralateral Variation of the Lisfranc Complex and Diagnostic Cutoffs for Subtle Instability Using 3D Weightbearing CT.

Abstract

Weightbearing computed tomography (WBCT) provides a dynamic evaluation through the comparison of the injured foot with the uninjured contralateral side under physiologic weight. This study aims to determine 3D WBCT Lisfranc variations among healthy individuals and determine WBCT measurement cutoff values to determine Lisfranc instability. In this retrospective study, 222 adult patients with bilateral foot WBCT were included: 32 cases (with Lisfranc instability) and 190 controls (with no current or prior midfoot injuries). Lisfranc complex WBCT volume (mm³), axial area (mm²), and diastasis (mm) across the medial cuneiform (C1) and second metatarsal (M2) were measured for both groups. The percentage difference between the injured and uninjured sides for each measurement was calculated for each patient. Cutoff values were determined using area under the receiver operator curve (AUC). Demographic data had no association with the percentage difference of all 3 measurements. There were significant differences between cases and controls for all 3 WBCT measurements (<i>P</i> < .001). The cutoff values were found to be 20%, 26%, and 34%, for volume, area, and diastasis, respectively. Diastasis resulted in the greatest area under the curve (AUC = 0.905) and a corresponding sensitivity and specificity of 0.813 and 0.900, respectively. In our study, we found a median physiologic difference of up to 12% between contralateral feet of healthy individuals. In the Lisfranc cohort, the median percentage difference was ≥32% across measurements; receiver operating characteristic analysis identified diagnostic cutoffs of 20% (volume), 26% (area), and 34% (diastasis). Therefore, measurements in the intermediate zone between 12% and 32% may warrant further assessment to prevent misdiagnosis and further morbidity. Between volume, area, and diastasis, diastasis showed the highest diagnostic performance (AUC = 0.90) for isolated Lisfranc instability.