Effect of a Controlled Ankle Motion Walking Boot on Syndesmotic Instability During Weightbearing: A Cadaveric Study

SLR - October 2019 - Raul Aviles

Reference: Lamer S, Hébert-Davies J, Dubé V, Leduc S, Sandman É, Ménard J, Nault ML.  Effect of a Controlled Ankle Motion Walking Boot on Syndesmotic Instability During Weightbearing: A Cadaveric Study. Orthop J Sports Med. 2019 Aug 20;7(8)

Scientific Literature Review

Reviewed By: Raul Aviles, DPM
Residency Program: SSM Health DePaul Hospital – Bridgeton, MO

Podiatric Relevance: Ankle injuries commonly occur in athletic and physically active populations. The syndesmosis is implicated in 1% to 25% of all ankle injuries. Syndesmotic injuries result in varying degrees of instability that if improperly treated can result in complications including early arthritis and prolonged pain. Successful management of such injuries is guided by the amount of ligaments involved. The ligaments include the anterior inferior tibiofibular ligament (AitFL), interosseous ligament (IOL), and posterior inferior tibiofibular ligament (PiTFL). Surgical intervention is required when all three ligaments are disrupted due to the large degree of instability. Immobilization in a CAM boot is adequate when the AiTFL alone is ruptured. When two ligaments are involved however, the use of a CAM may increase the diastasis and fail to maintain syndesmotic congruity resulting in associated complications. The aim of this study was to assess the effect of a CAM boot during axial loading at varying levels of syndesmotic instability.

Methods: A cadaveric study was performed on 10 lower extremity specimens. The specimens were dissected to allow exposure of the tibial plateau and syndesmosis and were fitted to a custom-made device that allowed a reproducible load of 750 N to be applied. Different ligamentous conditions were created by iatrogenic rupture of the syndesmotic ligaments, including the AiTFL and IOL. Ankles with intact syndesmosis, isolated AiTFL rupture, and combined AiTFL/IOL rupture were compared with and without axial loading and with and without CAM boot. A previously validated computed tomography measurement system was utilized to assess the distal tibiofibular relationship. Wilcoxon tests for paired samples and nonparametric data were used to compare the different conditions.

Results: No significant differences were found in the distal tibiofibular relationship when comparing the effect of axial loading and no axial loading on different ligamentous conditions. The only difference noted was an increase in the external rotation of the fibula using the CAM boot as observed with AiTFL rupture (8.40° vs 11.17°; P = 0.009) and combined AiTFL/IOL rupture (8.81° vs 11.97°; P = 0.005).

Conclusions: The authors conclude that axial loading alone, without rotational forces, in a CAM boot did not cause significant distal tibiofibular instability in the setting of AiTFL or combined AiTFL/IOL ruptures. Under physiologic conditions, ambulation produces axial and rotational forces about the syndesmosis. The observed external rotation of the fibula is believed to be the result of the CAM boot design, specifically the placement of the air cushions. Because of the aforementioned statements, clinical recommendations regarding use of CAM boot in syndesmotic injuries involving multiple ligaments cannot be made.