SLR - August 2019 - Gregory A. Foote

Relationship Between Fracture Morphology of Lateral Malleolus and Syndesmotic Stability After Supination-External Rotation Type Ankle Fractures

Reference: Chun, D.I., Kim, J., Kim, Y. S., Cho, J.H., Won, S.H., Park, S.Y., & Yi, Y. Relationship Between Fracture Morphology of Lateral Malleolus and Syndesmotic Stability After Supination-External Rotation Type Ankle Fractures. Injury. 2019 May 22. doi:10.1016/j.injury.2019.05.020

Scientific Literature Review

Reviewed By: Gregory A. Foote, DPM
Residency Program: University of Florida Health – Jacksonville, FL

Podiatric Relevance: Supination-external rotation (SER) ankle fractures are the most common pattern of ankle fracture encountered by the podiatric surgeon. Incidentally, these injuries display a high incidence of syndesmotic instability. Widening of the medial clear space has historically been the most accurate predictor of syndesmotic instability in the pre-operative examination. This study aimed to investigate additional factors for pre-operative detection of syndesmotic injury according to fibular fracture morphology in SER III and SER IV ankle fractures by using radiography and computed tomography (CT).

Methods: An IRB-approved trauma registry was used to perform a retrospective, clinical and radiological data review  on all operative SER III and IV ankle fractures treated by a single surgeon from 2009 to 2015. The ankle fractures were divided into stable and unstable groups based on CT evidence of tibio-fibular displacement at the syndesmosis. An unstable syndesmotic injury was confirmed intraoperatively via Cotton test with a tibio-fibular clear space of  greater than 5mm. On the preoperative radiographs, four parameters were measured to assess the fibular fracture patterns: (1) fracture height at the anterior fibular cortex, (2) fracture height at the posterior fibular cortex, (3) medial clear space widening, and (4) fragment angle between the fracture line and the posterior fibular cortex. The unstable and stable syndesmotic groups were compared and tested for statistical significance.  

Results: A total of 154 patients with an SER III, IV or SER IV equivalent ankle fractures underwent operative treatment between May 2009 and December 2015. One hundred and six ankles comprised the unstable syndesmosis group (68.8 percent) and 48 ankles comprised the stable group (31.2 percent). Fragment angle and medial joint space on CT were significant factors contributing to an unstable syndesmosis. Using a fragment angle of  less than 32.9 degrees on CT scan as a threshold, a sensitivity of 89.4 percent and a specificity of 72.6 percent was achieved to determine syndesmotic instability. Using a medial joint space cutoff of greater than 4.4mm on CT scan as threshold, a sensitivity of 85.4 percent and specificity of 80.2 percent was achieved to determine syndesmotic instability.

Conclusions: The authors concluded that medial clear space widening and angle of fibular fracture fragment showed significance in predicting syndesmotic injury. Specifically, they determined that the more acute the fragment angle, the higher probability of syndesmotic instability following fibular fracture fixation. If the fracture forms an acute angle, interosseous membrane damage may occur in a wider area and fracture size beneath the posterior fracture may be larger, which can cause unstable syndesmotic injury. As the acuity of the angle increases, the force transmitted also increases, resulting in a wider area of syndesmotic complex damage. This information is a useful adjunct to the measurement of medial clear space widening in predicting syndesmotic instability preoperatively. This allows the surgeon to establish patient expectations prior to the operation for the duration of immobilization, ambulatory status and outcomes following surgical intervention when syndesmotic fixation is imminent. Furthermore this will aid in preoperative planning in regard to the type of fibular fixation, location of screw placement and equipment availability prior to the operation. 

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