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.