Postoperative CT Is Superior for Acetabular Fracture Reduction Assessment and Reliably Predicts Hip Survivorship.

BACKGROUND: Postoperative pelvic radiographs are routinely used to assess acetabular fracture reduction. We compared radiographs and computed tomography (CT) with regard to their ability to detect residual fracture displacement. We also determined the association between the quality of reduction as assessed on CT and hip survivorship and identified risk factors for conversion to total hip arthroplasty (THA).
METHODS: Patients were included in the study who had undergone acetabular fracture fixation between 1992 and 2012, who were followed for ≥2 years (or until early THA), and for whom radiographs and a pelvic CT scan were available. Residual displacement was measured on postoperative radiographs and CT and graded according to Matta's criteria (0 to 1 mm indicating anatomic reduction; 2 to 3 mm, imperfect reduction; and >3 mm, poor reduction) by observers who were blinded to patient outcome. Kaplan-Meier survivorship curves were plotted and log-rank tests were used to assess statistical differences in survivorship curves between adequate (anatomic or imperfect) and inadequate reductions on CT. Cox proportional hazard regression analysis was used to identify risk factors for conversion to THA. Two hundred and eleven patients were included. At mean of 9.0 years (standard deviation [SD], 5.6; median, 7.9; range, 0.5 to 23.3 years) postoperatively, 161 patients (76%) had retained their native hip.
RESULTS: Compared with radiographs, CT showed worse reduction in 124 hips (59%), the same reduction in 79 (37%), and better reduction in 8 (4%). Of the 99 patients graded as having adequate reduction on CT, 10% underwent conversion to THA in comparison with 36% of those with inadequate reduction, and there was a significant difference between the survivorship curves (p < 0.001). Mean hip survivorship was shorter in patients ≥50 years of age (p < 0.001) and in those with an inadequate reduction on CT (p < 0.001). Independent risk factors for conversion to THA were age (hazard ratio [HR] = 4.46, 95% confidence interval [CI] = 2.07 to 9.62; p < 0.001), inadequate reduction (HR = 3.57, 95% CI = 1.71 to 7.45; p = 0.001), and posterior wall involvement (HR = 1.81, 95% CI = 1.00 to 3.26; p = 0.049). Sex, fracture type (elementary versus associated), and year of surgery did not influence hip survivorship.
CONCLUSIONS: CT is superior to radiographs for detecting residual displacement after acetabular fracture fixation. Hip survivorship is greater in patients with adequate (anatomic or imperfect) reduction on CT. Along with older age and posterior wall involvement, an inadequate reduction on CT is a risk factor for conversion to THA. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.