Effect of CAM boot immobilization on weightbearing stability in syndesmotic injuries

Abstract

Category: Trauma Introduction/Purpose: Ankle injuries are one of the most frequent traumas of the lower limb. They typically involve the lower lateral ligaments of the ankle, but the syndesmosis is also affected in up to 18% of cases. The degree of instability of syndesmotic joint depends on which ligaments are affected. Adequate management of syndesmotic injuries is crucial to avoid long term complications. The primary goal of our study was to evaluate the effect of simulated weightbearing on syndesmotic instability resulting from isolated AiTFL injury and from combined AiTFL/IOL injuries. The secondary goal was to evaluate the effect of a controlled ankle motion walking boot on syndesmosis stability following injury. We hypothesized that the CAM boot would prevent significant instability even in two ligaments injuries. Methods: Ten cadaveric specimens were dissected to expose the syndesmosis to create progressive iatrogenic syndesmosis ruptures. Uninjured syndesmoses were compared to isolated AiTFL and combined AiTFL/IOL ruptures. The specimens were fitted in a custom-made device to allow stabilization of the leg and apply a reproducible axial load (AL) of 750 N, equivalent to the weight of a 168-pound person. For each specimen and injury pattern, CT-scan images were obtained with and without AL, and with a CAM boot under AL. Distal tibio-fibular relationship was evaluated in three planes using a previously validated measurement system developed on CT. Wilcoxon tests for paired samples and non-parametric data were done to compare the different conditions. Results: For our first objective, when comparing ankles with isolated AiTFL to combined AiTFL/IOL rupture with and without AL, the only significant difference was an increase in internal rotation between the incisura and a line drawn in the axis of the fibula. Even with minimal statistical differences, it appears that axial loading does not impact syndesmotic stability apart from a slight increase in internal rotation with a single or two-ligament injury. As for our second end point, with the CAM orthopedic boot, no significant widening of the syndesmosis happened when either one or both ligaments were sectioned, in an axial loading state. We therefore confirmed our hypothesis that even with two syndesmotic ligament injuries, axial loading in a CAM boot does not affect distal tibio-fibular anatomy. Conclusion: This study reveals that weight bearing without rotational force does not affect the stability of the syndesmosis. Incomplete syndesmotic injuries can likely be treated with nonoperative treatment in a CAM boot and weight bearing as tolerated. Further clinical studies are needed to confirm these findings.