Distance and Coverage Mapping: A Novel Approach to Detecting Subtle Lisfranc Instability

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Assessment of subtle Lisfranc injuries and guiding surgical decisions remains challenging. Weightbearing CT (WBCT) is emerging as a valuable tool, yet recent studies rely on manual measurements, cadaveric models, or lack treatment differentiation. Traditional single-plane distance measurements may overlook subtle instability. Distance and Coverage Mapping (DM/CM) may detect those through detailed, three-dimensional (3D) assessments of joint congruency but have not been applied to Lisfranc injuries. In the present study DM and CM were used to analyze midfoot joints in patients with Lisfranc injuries who received conservative or operative treatment. We hypothesized differences would be found between injured and healthy contralateral feet, as well as between operatively and conservatively treated feet. Methods: This retrospective study analyzed bilateral WBCT scans of patients with acute, low-energy Lisfranc injuries, excluding those with previous midfoot injuries, surgeries, or arthritis. Semi-automated segmentation of the scans was performed, followed by manual selection of the opposing surfaces of eight Lisfranc complex regions: seven articulating (M1-C1, M2-C2, C1-C2, C2-C3, and each naviculocuneiform joint) and one non-articulating (C1-M2). M1-C1, M2-C2, and C1-C2 were further divided into four subregions. DM was performed in MATLAB by projecting a vector perpendicular from one triangulation until it intersected with its opposing triangulation. CM was measured by determining the percentage of distances < 4mm in each region. First, we compared injured and uninjured contralateral feet using paired t-tests, calculating effect sizes using Cohen’s d. Next, we directly compared DM and CM values between operatively and nonoperatively treated feet using t-tests assuming unequal variance. P-values < 0.05 were considered significant. Results: A total of 27 patients (18 female, 9 male; mean age 46 years, BMI 28.8) were included, with 15 treated operatively and 12 nonoperatively. Compared to the uninjured side, DM demonstrated significant widening in 9/20 regions in the operative group and 6/20 in the nonoperative group. The largest increase in the operative group was in C1-M2 (0.569mm, p=0.028), which was not significantly widened in nonoperative patients. Contralateral CM comparison demonstrated significantly reduced coverage in 8/20 regions for the operative group and 3/20 for the nonoperative group, with the greatest uncoverage at C1-M2 (-39.8%, p< 0.001). Conclusion: CM, a normalized metric, demonstrated greater utility than DM in differentiating injury severity. While DM assesses absolute joint space widening, CM normalizes joint congruency by measuring the percentage of opposing surfaces < 4mm. Contralateral comparisons identified injury-related changes, while direct operative vs. nonoperative group comparisons highlighted differences due to treatment selection. CM detected greater instability in surgically treated cases, demonstrating its potential as a clinical tool. Our findings suggest that CM can assess joint congruency without requiring contralateral comparison. However, prospective studies using CM/DM-based cut-off values in a decision-making algorithm and incorporating clinical follow-up are needed to validate their clinical utility. Visual Representation of Difference in C1-M2 Coverage in Operative and Nonoperative Lisfranc Patients (top), and summary of key findings (bottom)