Femoral head subchondral impaction on CT: what does it mean in patients with acetabular fracture?

To evaluate the prevalence of isolated femoral head impactions associated with acetabular fractures and to assess whether impactions may be predictive of the development of delayed major complications requiring total hip arthroplasty. A total of 128 consecutive adult patients with acetabular fracture and no femoral head fracture were included. Admission CTs were re-interpreted for the presence of hip dislocation and femoral head impactions. Radiological and clinical reports were reviewed in patients in whom conservative management of the femoral head was attempted, to determine if total hip arthroplasty was eventually required over a 48-month follow-up period. Univariate and multivariate analyses were performed to assess whether impaction is an independent predictor of failure of conservative management. Impaction was found in 40% of all patients (51 out of 128), in 58% of those with dislocation (19 out of 33), and in 34% of those without dislocation (32 out of 95; p < 0.05). One hundred and five patients underwent conservative management of the femoral head; 12.5% of them (13 out of 105) eventually required total hip arthroplasty. An impaction was present in 77% of the latter (10 out of 13) and in 33% of patients with successful conservative management (30 out of 92; p = 0.0042). At multivariate analysis, impaction and dislocation were significantly and independently associated with a higher risk for delayed total hip arthroplasty (odds ratio of 4.8 and 4.0 respectively). Femoral head impactions are frequently seen on CT of patients with acetabular fractures; they are independent predictive factors for the need for delayed total hip arthroplasty. They should be systematically mentioned in the CT report.