Session VII - Foot and Ankle

Intraoperative Diagnosis of Syndesmosis Injuries in External Rotation Ankle Fractures

Richard J. Jenkinson, MD; David W. Sanders, MD, FRCS(C); Mark D. MacLeod, MD, FRCS(C); Jeannette Lydestad, MD; University of Western Ontario, Health Sciences Center, London, Ontario, Canada

Purpose: Undiagnosed syndesmotic injuries can lead to late instability, pain, and arthrosis. Unfortunately, the diagnosis of ankle syndesmosis injuries associated with external rotation-type ankle fractures (OTA 44B and 44C) can be difficult. Static radiographs, biomechanical criteria, and stress radiographs have all been used to determine the need for syndesmotic fixation. This study was designed to compare intraoperative fluoroscopic stress testing, static radiographs, and biomechanical criteria, in diagnosing distal tibiofibular syndesmotic injuries associated with external rotation type ankle fractures.

Methods: Prospective recruitment of 40 skeletally mature patients with unstable unilateral external rotation ankle fractures was undertaken. Fractures were classified according to the AO-Weber and Lauge-Hansen criteria. Prior to surgery, the treating surgeon completed a form detailing his operative treatment plans including whether syndesmotic fixation would be necessary. Specifically in pronation-external rotation injuries, biomechanical (Boden) criteria were applied to predict syndesmotic instability. Intraoperatively, the injured and noninjured ankles were examined by using external rotation and valgus and anterior drawer stress tests under fluoroscopy. A standardized force was applied for the stress examination. Stress testing was performed after lateral malleolar fixation and repeated after medial and syndesmotic fixation, as required. The contralateral uninjured limb was used as a control. A 1-mm side-to-side difference in the radiographic clear space was defined as a positive stress examination. When ligamentous instability was detected, the treating surgeon would alter the fixation and postoperative treatment plan as required.

Results: The preoperative plan was altered by the use of fluoroscopy in 35% of cases. Intraoperative fluoroscopy detected unpredicted syndesmotic injuries in 30% of cases. We found the surgeons able to detect the minimum 1-mm side-to-side difference in each of these cases. In supination-external rotation (OTA 44B) injuries, unpredicted syndesmosis injuries were found in 29%. In pronation-external rotation injuries (OTA 44C), 44% were associated with syndesmotic disruption not predicted by biomechanical criteria. In one injury, biomechanical criteria predicted a syndesmotic injury but stress testing revealed the syndesmosis to be intact. In the unstable syndesmosis injuries, a side-to-side difference of 3.7 mm on external rotation stress examination was found. Rigid medial fixation, where possible, decreased radiographic clear-space opening to 1.9 mm. With syndesmotic fixation, the mean clear-space opening decreased to 0.5 mm (P <0.01). In no case was rigid bimalleolar fixation sufficient to stabilize the syndesmosis injury.

Conclusions: Use of preoperative radiographs and biomechanical criteria are unable to satisfactorily predict the presence or absence of unstable syndesmosis injuries. Rigid bimalleolar fixation improved but was not sufficient to stabilize syndesmotic injuries based on our criteria for syndesmotic stability. Intraoperative stress fluoroscopy is a valuable tool for detection of unstable syndesmotic injuries.