Acetabular Giant Cell Tumor Presenting with Protrusio Acetabuli: A Rare Case Report.

INTRODUCTION: Giant cell tumor of bone (GCTB) is a benign but locally aggressive neoplasm that predominantly affects the epiphyses of long bones. Pelvic involvement is uncommon, and acetabular GCTB presents particular diagnostic and therapeutic challenges because of the complex pelvic anatomy, proximity to neurovascular structures, and critical weight-bearing function of the hip. CASE REPORT: We report the case of a 50-year-old female who presented with progressive left hip pain, restricted movements, and inability to bear weight following a trivial fall. Radiographs and cross-sectional imaging demonstrated an extensive expansile lytic lesion involving the entire left acetabulum, with cortical thinning and breach, weight-bearing dome involvement, and protrusio acetabuli with medial migration of the femoral head. Computed tomography-guided core needle biopsy confirmed GCTB, Campanacci grade II-III. The patient underwent extended intralesional curettage using a high-speed burr with phenol as a local adjuvant. The resultant acetabular defect was reconstructed using structural corticocancellous and cancellous bone grafts, supplemented by an acetabular reinforcement cage and total hip replacement to restore acetabular stability, hip biomechanics, and limb length. RESULTS: At 6 months of follow-up, the patient demonstrated pain-free hip movement, restoration of limb length, satisfactory hip stability, and independent mobilization. Radiographs showed maintained implant position and no evidence of local recurrence or early mechanical failure. The functional outcome was excellent, with a Musculoskeletal Tumor Society score exceeding 25/30. CONCLUSION: Extensive acetabular GCTB with protrusio acetabuli represents a challenging surgical entity requiring individualized oncological and reconstructive planning. Extended intralesional curettage combined with local adjuvant therapy, structural bone grafting, acetabular cage reconstruction, and total hip replacement can provide satisfactory early functional and radiological outcomes in appropriately selected patients. Long-term clinical and radiographic surveillance remains essential because of the risk of delayed local recurrence and prosthetic complications.