The Role of Unexpected Infection in Acetabular Erosion After Hip Hemiarthroplasty

Background and objectives: Hemiarthroplasty (HA) remains one of the most common treatments for displaced femoral neck fractures in the elderly, providing pain relief, early mobilization and a low reoperation risk. Acetabular erosion is a recognized late complication of this procedure, but early cartilage wear and its potential relationship with infection remain poorly understood. The aim of this study was to describe the clinical and microbiological characteristics of patients who required conversion to total hip arthroplasty (THA) because of acetabular erosion and to analyze the possible role of unexpected infection as a contributing factor. Materials and methods: A retrospective observational study was performed including all patients treated between 2007 and 2019 who underwent conversion of a failed HA to THA due to acetabular erosion after femoral neck fracture. Microbiological analysis was performed in all cases through multiple intraoperative samples. Patients were classified into two groups, with and without infection, according to positive microbiological cultures. Results: Forty-four patients were included, with a median age of 80.5 years (74-85). The median time to acetabular erosion was 25.4 months (10.4-47.4). Infection was identified in six patients (13.6%), all within the first six months after fracture (p = 0.029). The median time to erosion was shorter in infected patients (4.0 versus 29.8 months, p < 0.001). No other demographic, functional, or implant-related variables were associated with infection. There were three re-revisions, two due to recurrent dislocation and one periprosthetic infection in a hip without unexcepted positive culture. All patients with positive intraoperative culture were successfully managed with antibiotherapy. Postoperative functional scores improved significantly in both groups. Fifteen patients (34.1%) died during follow-up. Conclusions: Early acetabular erosion after hemiarthroplasty may represent a manifestation of previously unrecognized low-grade infection, particularly in frail elderly patients. Despite advanced age and multiple comorbidities, conversion to THA achieved significant functional improvement with an acceptable complication rate. Prospective studies with larger populations are warranted to confirm the relationship between infection and early acetabular cartilage loss.