Comparison Between Weightbearing and Non-weightbearing Measurements for Evaluation of Tibiofibular Syndesmotic Injuries

Abstract

Category: Ankle Introduction/Purpose: The distal tibiofibular syndesmosis maintains the integrity of ankle mortise during weight bearing. Syndesmotic injuries are common and even slight malreduction are associated with long-term development of tibiotalar osteoarthritis. Radiographic as well as CT based measurements are being employed to detect syndesmotic injuries, however, subtle injuries are commonly overlooked. In the present study we intend to investigate whether measurements obtained from weight-bearing (WB) cone-beam computed tomography (CBCT) images are different from measurements obtained from NWB images in subjects with clinical suspicion of syndesmotic injury and “inconclusive” plain radiograph findings Methods: In this prospective study, following IRB approval, the injured ankles of 20 patients (10 men and 10 women; mean age: 46.1 years; range: 19-82) with persistent ankle pain following ankle trauma and clinical suspicion of syndesmotic injury underwent simultaneous WB and NWB CBCT scans. Following a detailed literature review, a set of 21 syndesmotic related measurements in all WB and NWB images, assessing fibular displacement in medio-lateral, cranio-caudal, antero-posterior planes were performed by three independent readers. Inter-observer and intra-observer reliabilities were evaluated by intra-class correlation (ICC) and Pearson/Spearman’s correlation, respectively. We used Paired student t-tests or Wilcoxon-rank-sum tests to compare the measurements from the two scans. Bootstrapping with 10000 samples was used to extract P-values for 99% uncertainty levels Results: we observed almost perfect intra-observer reliability for WB and NWB measurements (r = 0.8-0.98). Inter-observer reliability was significant for all measurement with overall fair to perfect agreement (ICC=0.36-0.97). Mean values of medio-lateral measurements including posterior tibiofibular distance, tibiofibular clear space and diastasis were significantly higher in WB images compared to NWB CBCT images (P-value< 0.05). Mean values of angular measurement, bi-malleolar angle, lateral clear space and fibular length were significantly lower in WB images (P-value<0.05). The difference between other measurements were not statistically significant. Conclusion: Of syndesmotic measurements available in the literature, certain measurements are different between WB and NWB CBCT examinations with moderate to perfect intra- and inter-observer reliability in post-traumatic ankles with clinical suspicion of syndesmotic injury and inconclusive plain radiographs. These measurements should be further investigated for detection of biomechanical instability associated with syndesmotic injury compared to those obtained from asymptomatic ankles