Assessing Lisfranc Instability With Triplanar Weightbearing CT Alignment: Standardized Second Metatarsal Dorsal Offset.
BACKGROUND: Subtle Lisfranc injuries may escape detection on conventional imaging. Weightbearing computed tomography (WBCT) offers 3-dimensional assessment under loadbearing conditions and may improve detection of instability. The interval between the medial cuneiform (C1) and the second metatarsal (M2) is commonly measured, but sagittal displacement of M2 relative to the intermediate cuneiform (C2) may provide additional information. METHODS: We retrospectively analyzed 31 patients with acute Lisfranc injuries who underwent bilateral WBCT. A new standardized measurement of the second metatarsal dorsal offset (M2DO) was performed following triplanar alignment of M2, measuring dorsal cortical offset relative to the second cuneiform. Two foot and ankle surgeons independently obtained measurements; 1 repeated all measurements after 2 weeks. Injured and uninjured sides were compared with paired t tests, and intra- and interobserver agreement was assessed with intraclass correlation coefficients (ICCs). RESULTS: The M2DO differed significantly between injured (0.71 ± 1.18 mm) and uninjured feet (-0.74 ± 0.66) (P < .0001). Reliability was almost perfect for intra- and interobserver assessments in injured feet (intrarater 0.92, interrater 0.94) and in the overall cohort (0.93 and 0.92), and substantial in uninjured feet (0.79 and 0.67). CONCLUSION: The M2DO is a reliable WBCT-based parameter for evaluating Lisfranc instability. It may supplement the triplanar C1-M2 method and thereby improve diagnostic accuracy and reproducibility. Future studies should establish thresholds for surgical decision-making and clinical application. LEVEL OF EVIDENCE: Level III, retrospective diagnostic study.
