How Valuable is the CT? Assessment of the Presence of Posterior Malleolar Fractures in Plane Radiographs

IntroductionThe involvement of the posterior malleolus (PM) in dislocated bimalleolar ankle fractures is associated with inferior clinical outcomes. There is no consensus on whether and when a computed tomography (CT) scan should be performed in the case of an inconspicuous X-ray of the PM. How high is the risk of missing a posterior malleolus fracture (PMF) without a CT scan? The aim of this study was hence to analyze the rate of correctly performed assessments of the PM in bimalleolar ankle fractures based on X-rays and to correlate this with surgical therapy.Materials and MethodsIn total, 100 bimalleolar ankle fractures, 50% with and 50% without PMF visible on the basis of a CT scan, were analyzed by 4 observers at 2 different time points 30 days apart (d1 and d2). The observers had to decide on the basis of X-rays whether a PMF was present or not. This was followed by a correlation with the operative treatment.ResultsAnalyzing each observer independently, the correct diagnoses of a present PMF were made in an average of 83% of cases, with no significant difference between seniors and residents. In 22 of 50 cases (44%) with a PMF confirmed on a CT scan, it was missed by at least one of the observers based on plain radiographs. For those PMF that required fixation (24 of the 50 PMF), in 25% of cases, at least 2 observers missed the diagnosis of a PMF.ConclusionsBased on our results, there are deficits in the detection of PMF in bimalleolar ankle fractures only on the basis of X-rays, even in PMF that were later fixed surgically. This study aids the awareness that PMF can be easily missed on X-rays and raises the question of whether a CT scan might become mandatory in distal fibula fractures that involve the upper ankle joint.Levels of Evidence:Level III: Retrospective study.