Catastrophic Acetabular Osteolysis and Component Migration Secondary to Surgical Cup Malpositioning: A Case Report.

Severe periprosthetic osteolysis and component migration present major technical challenges during revision total hip arthroplasty (THA). We report the case of a 45-year-old man who presented with a two-week history of rapidly escalating left hip pain, severe restriction of mobility, and complete inability to tolerate weight-bearing. Eight years earlier, the patient had undergone primary THA, followed three years later by a limited revision consisting of a modular head and liner exchange with retention of the original press-fit acetabular shell. Clinical evaluation revealed 2.5 cm of shortening of the left lower extremity, without localized or systemic signs of infection. Preoperative serum inflammatory markers (erythrocyte sedimentation rate (ESR), 11 mm/h; C-reactive protein (CRP), 3.1 mg/L) were within normal reference ranges, reducing the likelihood of overt periprosthetic joint infection (PJI). However, in the absence of joint aspiration and routine intraoperative cultures, low-grade PJI could not be definitively excluded. Diagnostic imaging demonstrated catastrophic acetabular osteolysis with superior-lateral migration of the component, which was formally classified as a Paprosky Type IIIA acetabular defect. At presentation, the acetabular shell exhibited severe lateral inclination (62°), representing a plausible biomechanical mechanism for edge loading and particle-induced osteolysis. Reconstruction was performed with thorough debridement, placement of three porous trabecular titanium augments with impacted morselized bone graft matrix, and multi-screw transacetabular fixation of a revision cup, restoring the anatomical center of rotation and leg length. Following an institutional protocol of six to eight weeks of protected weight-bearing, early post-discharge follow-up demonstrated restored joint stability and pain relief. This case illustrates the biomechanical consequences of severe component malpositioning and demonstrates effective reconstruction strategies for massive uncontained acetabular defects.