Weight Bearing Cone Beam Computed Tomography (CBCT) of the Distal Tibiofibular Syndesmosis – Differentiating Between Stable and Unstable Syndesmotic Ankle Injuries
Authors: Raheman Firas , Dhillon Govind , Mangwani Jitendra , Ahluwalia Raju 
Published: December 2024

Category: Ankle; Trauma Introduction/Purpose: Cone beam CT (CBCT) offers volumetric assessment in a single rotation, unlike conventional CT, which involves multiple slices. This enables a comprehensive three-dimensional evaluation of physiological functional anatomy under weight-bearing (WB) conditions, potentially revealing subtle changes undetectable on non-weight-bearing scans. This study aims to (A) identify normal WBCT metrics of the distal Tibiofibular Syndesmosis in uninjured ankles and (B) assess the impact of syndesmotic injuries on the tibiofibular relationship at the syndesmosis level during weight bearing. Methods: This study followed PRISMA guidelines. It included patients aged 18 or older with unilateral ankle injuries who underwent weight-bearing CBCT for occult fractures or syndesmotic instability, compared to their uninjured contralateral side. Additionally, a control group of patients with fore or midfoot injuries undergoing weight-bearing CBCT was included. Data were analyzed using Stata v17 (StataCorp LLC). Meta-analyses using the metan package (Stata Corp) estimated pooled normal CBCT metrics for both uninjured and injured ankles. A random-effects restricted maximum likelihood ratio model assessed scalar metrics and measurements performed on all ankles imaged using weightbearing CBCT. Forest plots illustrated standardized mean differences between weightbearing metrics of injured and uninjured ankles, with pooled estimates obtained with 95% CIs. Generalized linear modeling with Gaussian families evaluated the effect of participant factors on scalar CBCT metrics. Results: 559 ankles, with 408 uninjured patients and 151 patients with syndesmotic instability, were reviewed. The normal syndesmosis area averaged 112.54mm2 (95%CI 104.59-120.49), contrasting with 157.52mm2 (95%CI 133.79-181.24) for ankles with syndesmotic injury (p< 0.01; I2 =0.00%). The standardized mean difference of syndesmotic area between injured and contralateral uninjured sides was 29.49mm2 (95%CI 19.52-39.46). Weight-bearing CT effectively differentiated syndesmotic injury, as evidenced by observed standardized mean differences for anterior tibiofibular distance (ATFD) (p=0.01), posterior tibiofibular distance (PTFD) (p=0.01), fibular rotation (p=0.02), and syndesmotic area (p< 0.001). Additionally, increasing age correlated with a reduction in normal syndesmotic area (β = 0.755, p=0.04). Conclusion: Syndesmotic area measurement proved most reliable, showing consistency across studies. Age-related declines underscore the need for stratified assessment, particularly in older patients, to prevent diagnostic oversights. Dynamic changes during weight bearing aid early detection and management. Syndesmotic stability assessment is crucial, as persistent instability often requires surgery. Current imaging falls short under stress, but weight-bearing CT shows promise. Normal metrics for weight-bearing CT of the uninjured tibiofibular joint lack consensus due to novelty. However, diastasis, fibular rotation, fibular translation, and syndesmotic area measurements consistently provide reliable results. Syndesmotic area measurement is notably reproducible, making it a valuable composite metric.