3D Weightbearing CT for the Diagnosis of Lisfranc Instability: An Update

Abstract

Category: Midfoot/Forefoot; Other Introduction/Purpose: Lisfranc instability is often a challenging injury to diagnose, with up to one-third being missed on initial evaluation. Lisfranc instability is assessed by widening of the space between the second metatarsal base and the medial cuneiform. This space is visualized on X-Ray; however, in subtle Lisfranc instability cases computed tomography (CT) imaging is often obtained. Given the 1D nature of diastasis measurement, X-ray should be an adequate means of evaluating this widening, yet clinical practice suggests weightbearing CT (WBCT) is more sensitive. This suggests the 3D location of the diastasis measurement is crucial. This study aimed to first compare weight-bearing X-ray and WBCT diastasis and area measurements of the Lisfranc complex, and second to compare WBCT diastasis measurements at various locations in the coronal plane. Methods: A total of 90 patients with both weight-bearing foot X-ray and bilateral foot WBCT were included: 37 patients had confirmed Lisfranc instability, and 53 patients had no history of midfoot injury. Lisfranc instability was confirmed intraoperatively or by clinical examination performed by the surgeon. For all 90 patients, the interosseous diastasis and area between the medial cortex of the second metatarsal and the lateral cortex of the medial cuneiform were measured on both weightbearing X-ray and axial slices of WBCT. For a subset of patients (12 in each cohort) the diastasis between second metatarsal and medial cuneiform was measured at 4 distinct axial locations using coronal slices of the WBCT (Figure 1). Results: A Wilcoxon test comparison of diastasis and area measurements on weightbearing X-ray and axial slices of WBCT revealed a significant difference in the weightbearing X-ray and WBCT measurements (p < 0.001) for both the control and Lisfranc cohorts. A comparison of weightbearing X-ray diastasis to dorsal, interosseous, and plantar diastasis measurements on coronal slices using Kruskal Willis analysis for the control cohort revealed a significant difference in all three measurements (Figure 1, p-values listed). Kruskal Willis analysis of the Lisfranc cohort demonstrated a significant difference between the X-ray diastasis and the plantar WBCT diastasis (p=0.01), but no difference from interosseous (p=0.08) or dorsal (p=0.33) diastases. A comparison of the axial WBCT diastasis measurements compared to the three coronal diastasis measurements revealed no difference in either cohort. Conclusion: Our results showed that for assessing the Lisfranc joint in subtle cases and healthy individuals, WBCT remains the most accurate imaging tool. However, in patients with confirmed Lisfranc instability, X-ray measurements are more reliable if the instability is at the dorsal and interosseous levels and not the plantar level. Hence, to assess the Lisfranc joint at different levels, WBCT has superiority over X-ray. Additionally, the axial diastasis of the Lisfranc joint on WBCT seems similar to coronal diastasis rendering both views reliable for measurements.