Commentary on an article by Young Choi, MD, et al.: “Preoperative Radiographic and CT Findings Predicting Syndesmotic Injuries in Supination-External Rotation-Type Ankle Fractures”

The ability to reliably predict the presence of an unstable syndesmotic injury prior to surgery as a component of an ankle fracture has been elusive for many years. This confusion stems from the dogma that orthopaedic surgeons have followed for years based on the Lauge-Hansen¹ and Danis-Weber^2,3 classification systems. The authors of the current paper have done a commendable job of creating a real-world retrospective analysis of 191 patients with bimalleolar supination external rotation (SER) fractures that had undergone operative intervention. This study contrasts with many of the cadaveric studies of the past that have attempted to answer questions about the predictability of the presence of syndesmotic injuries correlative to the pattern of injury demonstrated on radiographs. Conclusions drawn from cadaveric work that resulted in the Lauge-Hansen and Danis-Weber classification systems may not always correlate with ankle fracture findings encountered during clinical scenarios. Syndesmotic injuries are frequently encountered in both Danis-Weber type-B and SER type-II injuries. The presence of syndesmotic injuries in these fracture patterns defies traditional classification systems.

In the present study, the patients’ preoperative radiographs and computed tomography (CT) scans of the injured ankle were analyzed for the fracture height from the tibial articular surface to the distal aspect of the fibular fracture, the degree of bone attenuation (bone density) of the fibular shaft, and separation of the talus from the medial malleolus. Binary logistic regression analysis was performed to determine which of these factors would predict syndesmotic instability.

Prediction of syndesmotic instability might better prepare the surgical team in planning patient positioning, surgical instrumentation, postoperative management, and the necessity for future hardware removal. In addition, the ability or inability to participate in athletics and work might be predicted on the basis of improved preoperative analysis of certain variables.

The binary logistic regression model, including age, sex, mechanism of injury, fracture height on CT scans, fracture length on CT scans, medial joint space on CT scans, and bone attenuation of the lateral malleolus, showed that fracture height, medial joint space, and osseous attenuation of the lateral malleolus were significant contributing factors to unstable syndesmotic injury in SER-type ankle fractures. The threshold measurements for predicting an unstable syndesmotic injury on the CT scan were a fracture height of >3 mm and a medial joint space of >4.9 mm. When fracture height was >7 mm or the medial joint space was >4.5 mm wide on radiographs, unstable syndesmotic injuries should be suspected, appropriately evaluated, and managed at the time of ankle fracture surgery.

The difference between the measurements on CT scans or radiographs in this study can be explained by the two-dimensional nature of radiographs compared with the three-dimensional nature of CT scans. The most proximal and medial bone landmarks can be measured more accurately from osseous landmarks with a CT scan. The measurements obtained from radiographs during clinical situations can vary according to patient positioning and radiographic technique. These parameters should be considered in clinical situations. A CT scan is not warranted in the majority of these clinical situations, but can be ordered in questionable situations or in light of poor radiographs. In addition, making similar radiographs of the noninjured extremity can provide a basis for comparison as a baseline for an individual patient. The exposure fields and distance from the cassette should be the same for both extremities.

Bone attenuation measurement on the CT scan is a novel variable introduced in this study compared with earlier studies of this type of injury. The authors concluded that denser fibular bone correlated with an increased prevalence of syndesmotic disruptions theorizing that the stronger bone failed after the weaker syndesmosis was disrupted. When the fibular bone was of lesser density on the subjective CT scan measurement, the fibula fractured below the level of the ankle joint and left the syndesmosis intact.