Retrospective Chart Review: Weight Bearing CT Scans and the Measurement of the Tibiofibular Syndesmosis

CATEGORY: Ankle INTRODUCTION/PURPOSE: Tibiofibular Syndesmosis injuries are commonly misdiagnosed due to their unreliable projection on plain films. Many studies have striven to establish baseline measurements of the distal tibial and fibular articulation. 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 hypotheses of this study are: 1. Standing, weight bearing CT scan will allow for evaluation and measurement of the tibio-fibular syndesmosis. 2. There will be no side to side variation or sex-based differences in syndesmosis measurements. 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 twenty ankle 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 tibiofibular syndesmosis on weight bearing CT. Averages were found for measurements of anterior incisura 3.2mm (SD=1.1mm), middle incisura 3.9mm (SD=1.1mm), posterior incisura 5.6mm (SD=1.7mm), alpha angle 16.3° (SD=6.3°), medial clear space 2.2mm (SD=0.6mm).Patients with syndesmotic injuries had significantly larger measurements for anterior (p<0.0001), middle (p=0.0007), and posterior incisura (p=0.002) when compared to uninjured ankles. Males had significantly higher medial clear space widening (p=0.0012) compared to female patients. Anterior incisura (p <0.0001), posterior incisura (p=0.0005) were found to significantly decrease as age increased. CONCLUSION: This study aims to assist in defining baseline anatomic measurements for syndesmotic parameters. The values and comparisons obtained were able to reinforce that weight bearing CT is valuable in identifying subtle injuries to the TFS 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.