Using Area and Volume Measurements on Weightbearing CT to Detect Isolated Lisfranc Instability

Abstract

Category: Midfoot/Forefoot; Sports; Trauma Introduction/Purpose: Early detection of Lisfranc instability is critical for optimizing clinical outcomes. Injuries causing a more subtle instability, however, can be difficult to diagnose. The aim of this study was to compare the injured Lisfranc joint to the healthy contralateral side using weightbearing computed tomography (CT) in patients with known Lisfranc instability. We also aimed to define the range of normal measurement variation by comparing the Lisfranc joint measurements between the left and right foot in individuals without foot injury who underwent similar imaging. Our hypothesis was that compared to the healthy contralateral side, weightbearing CT area and volume measurements were increased in patients diagnosed with subtle Lisfranc instability. Methods: Patients with unilateral Lisfranc instability requiring operative fixation (n = 14) underwent preoperative bilateral foot and ankle weightbearing CT. A separate group of patients without foot injury who also underwent similar imaging were included as comparative controls (n = 36). For each weightbearing CT, 2 dimensional axial and coronal plane Lisfranc joint parameters, Lisfranc area, intercuneiform area, C1-M2 distance, C1-C2 distance, M1-M2 distance, first and second tarsometatarsal (TMT 1 and 2) alignment; and first and second tarsometatarsal (TMT 1and 2) dorsal step off were measured to evaluate the Lisfranc anatomy at a level 10 mm below the dorsal surface of medial cuneiform (Figures I and II). In addition, the volume of the Lisfranc joint was also evaluated. Values were recorded by two independent observers to assess interobserver reliability. Results: Among those with unilateral Lisfranc instability, values differed largely between the injured and the healthy contralateral side for all measurements performed (p-value range, 0.008 - <0.001). In the control population without foot injury, no differences were identified between any of the bilateral measurements (p-value range, 0.121 - 0.984). Conclusion: Weightbearing CT can effectively differentiate Lisfranc instability from those without instability. The Lisfranc volume and area had the largest difference between the injured and the uninjured feet among surgically treated patients with substantial interrater agreement making them the most relevant parameters for detecting Lisfranc instability. However, prospective studies are needed to validate the role of weightbearing CT in the diagnosis of subtle Lisfranc instability.