Retrospective Chart Review: Weight Bearing CT Scans and the Measurement of the Lisfranc Ligamentous Complex

CATEGORY: Midfoot/Forefoot INTRODUCTION/PURPOSE: Lisfranc Ligamentous Complex injuries are commonly misdiagnosed due to their unreliable projection on plain films. Many studies have striven to establish baseline measurements of the frequently injured articulations. While cadaver, MRI, ultrasound, and non-weight bearing computer tomography (CT) have been utilized, weight bearing CT (WBCT) scans are a relatively new imaging modality that has not yet been utilized to establish reproducible and widely-referenced baseline anatomic positions. The hyoptheses of this study are: 1. Standing, weight bearing CT scan will allow for evaluation and measurement of the Lisfranc joint complex. 2. There will be no side to side variation or sex-based differences in the Lisfranc joint complex. METHODS: A retrospective chart review was conducted using the electronic medical record. Inclusion criteria was applied as follows: patients who have undergone weight bearing CT of the bilateral lower extremities from 2018 to 2020. One hundred twelve foot CT scans were acquired for measurements. Measurements were collected by two independent reviewers twice in order to achieve inter- and intra-reliability. The measurements were then analyzed in order to establish a baseline for normal anatomy, compare injured to non-injured side, and observe any sex-based differences. RESULTS: Measurements of uninjured legs were utilized to define normal parameters for Lisfranc ligamentous complex (LLC) injuries. Averages were found for measurements of base 1 to 2 MT 2.7mm (SD=0.7mm), medial cuneiform to 2nd MT [M2-C1] 3.7mm (SD=0.7mm), intercuneiform distance 1.2mm (SD=0.3mm), sagittal descent 12.2mm (SD=5.4mm).Patient's with injury to LLC had a larger base of M1-M2, distance from base of first metatarsal to base of second metatarsal (Δ=.5903, p <.0001) and M2- C1 interval (Δ=1.8008, p<0.0001). Males had significantly higher M2-C1 (p=0.0031), intercuneiform distance (p=0.0039), and sagittal descent (p=0.0008) compared to female patients.No significant differences were found with regard to left vs right side in any of the measurements. Intercuneiform distance (p=0.0039) was found to significantly decrease as age increased, while sagittal descent significantly increased with increased age (p=0.0066). CONCLUSION: This study is one of the first investigations aims to assist in defining baseline anatomic measurements for Lisfranc ligamentous complex parameters on WBCT. The values and comparisons obtained were able to reinforce that weight bearing CT is valuable in identifying subtle injuries to the LLC while also demonstrating that there is male-to-female and age-related differences that should be kept in mind when radiographically evaluating imaging studies of injured patients.