Computed tomography versus plain radiography assessment of acetabular fracture reduction is more predictive for native hip survivorship

INTRODUCTION: Computed tomography (CT) is more accurate than plain pelvic radiography (PXR) for evaluating acetabular fracture reduction. As yet unknown is whether CT-based assessment is more predictive for clinical outcome. We determined the independent association between reduction quality according to both methods and native hip survivorship following acetabular fracture fixation. MATERIALS AND METHODS: Retrospectively, 220 acetabular fracture patients were reviewed. Reductions on PXR were graded as adequate or inadequate (0–1 mm or > 1 mm displacement) (Matta’s criteria). For CT-based assessment, adequate reductions were defined as < 1 mm step and < 5 mm gap, and inadequate reductions as ≥ 1 mm step and/or ≥ 5 mm gap displacement. Predictive values and Kaplan–Meier hip survivorship curves were compared and risk factors for conversion to total hip arthroplasty (THA) were identified. RESULTS: Mean follow-up was 8.9 years (SD 5.6, range 0.5–23.3 years), and 52 patients converted to THA (24%). Adequate reductions according to CT versus PXR assessment were associated with higher predictive values for native hip survivorship (92% vs. 82%; p = 0.043). Inadequate reductions were equally predictive for conversion to THA (33% for CT and 30% for PXR; p = 0.623). For both methods, survivorship curves of adequate versus inadequate reductions were significantly different (p = 0.030 for PXR, p < 0.001 for CT). Only age ≥ 50 years (p < 0.001) and inadequate reductions as assessed on CT (p = 0.038) were found to be independent risk factors for conversion to THA. Reduction quality as assessed on PXR was not found to be independently predictive for this outcome (p = 0.585). CONCLUSION: Native hip survivorship is better predicted based on postoperative CT imaging as compared to PXR assessment. Predicting need for THA in patients with inadequate reductions based on both assessment methods remains challenging. While both PXR and CT-based methods are associated with hip survivorship, only an inadequate reduction according to CT assessment was an independent risk factor for conversion to THA.