Three-Plane Alignment of the Second Metatarsal Improves Reliability of Weightbearing CT Measurements in Lisfranc Injury Assessment.

Background: Lisfranc injuries pose diagnostic challenges, particularly in evaluating joint stability. Conventional weightbearing computed tomography (WBCT)-based distance measurements of the C1-M2 interval fail to account for the second metatarsal's triplanar orientation, potentially leading to inaccuracies. This study introduces a new 3D-corrected triplanar measurement method correcting for axial, coronal, and sagittal alignment to improve diagnostic accuracy.

Methods: In this retrospective study, 31 patients with acute Lisfranc injuries underwent bilateral WBCT. Injuries were defined based on radiographic findings in the first to third tarsometatarsal joints and the C1-M2 interval. Two fellowship-trained foot and ankle surgeons independently performed manual measurements using a previously described uniplanar method and a new triplanar technique, applied proximally and distally in the C1-M2 interval. Intra- and interrater reliability were assessed via intraclass correlation coefficients (ICCs), and side-to-side differences were compared using paired statistical tests.

Results: The triplanar method demonstrated higher ICCs (intraobserver: 0.96-0.97; interobserver: 0.94-0.97) than the uniplanar method (intraobserver: 0.86-0.91; interobserver: 0.84-0.90), with distal measurements showing the highest reliability. Notably, the uniplanar method incorrectly measured the M1-M2 interval instead of the intended C1-M2 interval in 22.6% of injured feet. No such errors occurred in contralateral feet or with the triplanar method, which demonstrated 100% intra- and interobserver agreement. All 6 performed C1-M2 measurements showed significant differences between injured and contralateral feet (P < .05). The triplanar method applied distally in the coronal plane yielded the greatest absolute side-to-side difference (1.81 mm, SD 1.60).

Conclusion: This study demonstrates excellent intra- and interobserver reliability for a novel WBCT-based method that realigns the measurement planes with the second metatarsal rather than the floor. This method improves measurement precision and prevents systematic errors observed with previous techniques, particularly the misidentification of the M1-M2 interval using uniplanar methods. Clinical validation studies correlating measurements with surgical outcomes are needed to establish diagnostic thresholds and confirm clinical utility.

Level of evidence: Level III, retrospective diagnostic study.