Occult pelvic fractures following primary total hip arthroplasty: A retrospective CT-Based cohort study.

Introduction: Postoperative pelvic fractures are a rare but under-recognized complication of total hip arthroplasty (THA), particularly in the setting of cementless, press-fit acetabular components. This study aimed to determine the incidence, radiographic detectability, risk factors, and early clinical impact of occult pelvic fractures following primary THA. Methods: In this retrospective cohort, 60 primary THAs (59 patients) performed by a single surgeon at a tertiary center between June 2024 and September 2025 were evaluated. All patients underwent posterolateral THA using a hemispherical uncemented acetabular component with routine screw augmentation. Immediate postoperative radiographs and pelvic CTs were obtained, and images were independently reviewed by a dedicated musculoskeletal radiologist and a second radiologist to identify pelvic fractures and assess agreement. Demographics, comorbidities, surgical factors, and early postoperative outcomes were recorded. At 6 weeks, pain (VAS), Oxford Hip Score, and EQ-5D-based quality-of-life scores were collected. Multivariable logistic regression explored associations between fractures, risk factors, and early outcomes. Results: Occult pelvic fractures were identified on CT in 22 of 61 hips (36.1%), whereas radiographs detected fractures in only 10% of cases. Fractures most commonly involved the ilium, followed by the posterior column and pubic rami. Interobserver agreement for fracture detection on radiographs was high by percentage (90%). No individual patient-, operative-, or early postoperative factor was independently associated with fracture occurrence. At 6 weeks, there were no statistically significant differences in pain scores, functional PROMs, or use of assistive devices or opioids between patients with and without occult fractures. Conclusion: We found that occult pelvic fractures were common after a THA, but did not lead to worse functional or clinical outcomes. In addition, we determined that postoperative radiographs dramatically under-detect postoperative acetabular fractures. We were unable to find independent predictors (patient-, operative- and postoperative factors) of postoperative acetabular fractures.