Plain radiographic interpretation in trimalleolar ankle fractures poorly assesses posterior fragment size

Twenty-five patients with trimalleolar ankle fractures were evaluated using both conventional radiography and computed tomography (CT) to determine the size of the posterior fragment along with other fracture characteristics. Plain radiograph measurements indicated very poor inter- and intraexaminer reliability. When compared to the CT scan measurement, 54% of the plain radiographic readings revealed > 25% error. Plain radiographic interpretations erred in most cases by overrating the size of the fragment, but major underestimations also occurred. The larger size fragments showed more error than the smaller ones. This information confirms our clinical suspicion that the lateral radiograph is unreliable in assessing the posterior fragment size.