Change in the C1-M2 Distance after Simulated Purely Ligamentous Lisfranc Injury as Evaluated by Weightbearing CT Scans: A Match-Paired Cadaveric Study

Abstract

Category:Trauma; Midfoot/ForefootIntroduction/Purpose:Introduction: The incidence of Lisfranc injury is higher than previously estimated, and more than two- thirds of these injuries are caused by low-energy trauma. This low-energy mechanism, common to the athletic population, tends to be distinctly characterized by a primarily ligamentous Lisfranc injury. Bilateral weightbearing radiographs are widely accepted as the gold standard and are able to diagnose instability by contralateral comparison. However, contrary to radiography, CT imaging is not obscured by metatarsals overlapping each other and their adjacent tarsal bone and thus provides a better visualization of bony structure. This study’s purpose was to model a purely ligamentous Lisfranc joint injury to determine widening between the medial cuneiform (C1) and second metatarsal (M2) after each ligament dissection under non-weightbearing (NWB, 0 kg), partial weightbearing (PWB, 40 kgs.), and full weightbearing (FWB, 80 kgs.) conditions evaluated by weightbearing computed tomography (WBCT).Methods:Methods: Twelve paired through-knee cadavers were incised dorsally to visualize the Lisfranc joint complex. An intact ligament condition was the control (group 1). The dorsal ligament (group 2), interosseous ligament (group 3), and plantar ligament (group 4) were sequentially dissected. The twelve pairs were then equally randomized (groups 5a, 5b, and 5c). The first tarsometatarsal joint capsule (group 5a), the second tarsometatarsal joint capsule (group 5b), or the intercuneiform ligament (group 5c) was transected. The remaining intact ligaments of each subgroup were similarly randomized for transection (e.g., group 6ac: transection of the first tarsometatarsal joint, followed by transection of the intercuneiform ligament). Finally, the last ligament was transected (group 7). After each dissection, CT scans were taken for NWB, PWB, and FWB conditions. Distance between the lateral border of C1 and the medial border of M2 was used to evaluate diastasis for both coronal and axial views. Analysis of variance (ANOVA) tested for significant differences between all groups. Dependent t-test evaluated for significance of the weightbearing variable.Results:In group 1, C1-M2 distance was 3.9 mm (3.5-4.3, SD 0.3) for coronal imaging and 4.0 mm (3.6-4.5, SD 0.4) for axial imaging, and no statistically significant differences were found between paired feet (P = 0.61) or for weightbearing conditions (P = 0.34). In group 4, an average widening of 1.4-mm (0.8-2.1 mm, SD 0.4) and 1.8-mm (1.4-2.8 mm, SD 0.5) were observed for PWB and FWB in the coronal view, and an average widening of 1.5-mm (0.9-2.3 mm, SD 0.5) and 2.0-mm (1.4-3.0 mm, SD 0.5) were observed for PWB and FWB in the axial view, respectively. For the subsets of group 5, only 5c was found to have a majority of specimen (7/8, 87.5%) that had significant widening - at least 2 mm - between C1-M2 for the PWB condition in the axial view; for the FWB condition, significant widening was found in both the axial and coronal view. In groups 6ca, 6cb, and 7, a significant widening - at least 2 mm - was measured in both planes for the NWB condition.Conclusion:WBCT scans improve the ability to detect incomplete ligamentous Lisfranc injuries by comparing C1-M2 distance to the uninjured side. Widening exceeding 1 mm more than the normal contralateral side for the PWB condition could clinically indicate complete Lisfranc ligament injury (sensitivity 83.3%, specificity 88.9%, accuracy 87.5%).