Not Every Trimaelleolar Ankle Fracture Needs a CT Scan

X-rays can be an effective screening tool for posterior malleolus fractures, reducing the need for a computerized tomography (CT) scan, according to new data presented at the 2021 annual meeting of the American Academy of Orthopaedic Surgeons.

“Ankle fractures are common injuries, yet no objective, evidence-based protocol exists to identify whether a CT scan is necessary to make appropriate preoperative decisions,” the researchers wrote.

“If a posterior malleolus fracture (PMF) is present on plain X-ray imaging, the decision to further evaluate the ankle injury with a CT scan is often made based on an estimation of the PMF fracture size and surgeon preference.”

Surgical fixation of a posterior malleolus fracture is generally considered necessary for larger fractures of greater than 25% of the distal tibial articular surface. Previous studies, however, have shown that the size of a fracture requiring fixation can vary between 4% and 39%.

In the study, “Does Every Trimalleolar Ankle Fracture Need a CT, Or Are X-Rays Good Enough?” presented at a poster session during the meeting, the researchers sought to identify characteristics and measurements on plain radiograph that would indicate the need for advanced imaging to determine the preoperative plan. The goal they said was to reduce unnecessary imaging and costs.

The retrospective, observational cohort study evaluated adult ankle injuries treated at a level 1 trauma center during a two-year period. Pilon fractures, adjacent polytraumas, pathological fractures and those with a history of previous ankle injury or osteoarthritis were excluded.

Study data was collected from medical records and included demographics, risk factors, post-reduction x-ray measurements and CT measurements. CT measurement and the decision to perform PMF fixation were considered the gold standard for measurement and diagnosis.

Overall, 48 patients were included in the final analysis. The researchers found that the X-rays alone showed good ability to determine which patients required PMF fixation. No fractures with a PMF width on radiographs less than 20% required plate fixation after evaluation with CT except for one patient with an incarcerated fragment. The incarcerated fragment, however, was visible on plain films.

In addition, PMF width on X-rays showed good overall performance as a screening tool with a cutoff of 20% producing a sensitivity of 94-73% and specificity of 96.55%,

The Receiver Operating Characteristic curve for PMF width percentage on X-ray demonstrated excellent performance, with an Area Under Curve of 97.5%. The Spearman Rank Correlation also had a good relationship between PMF width percentage on radiograph and CT (R2 = 0.642).

They reported that in their patient cohort reducing CT usage to only those with PMF width percentage above 20% on the lateral view or those with incarcerated fragments would have reduced CT utilization by 54.2% without missing any large fractures that would require plate fixation.

The data also showed that the mean PMF width percentage between patients fixed with a plate and those without PMF fixation were 0.31 ± 0.05 and 0.12 ± 0.09, respectively; p < 0.001). Talus subluxation, age, open injury, and sagittal angle were not significantly significant for predicting plate fixation and the need for a CT prior to surgery.

“This study demonstrates that PMF width percentage on lateral radiograph alone is both sensitive and specific for determining the need for PMF fixation. Below 20%, a dedicated CT rarely changes management in the absence of other factors (e.g., obvious incarcerated fragment). By limiting perioperative CT to those with PMF width >20%, we could reduce CT utilization by as much as 54.2% without negatively affecting patient care,” the researchers wrote.