Bilateral Avascular Necrosis of the Femoral Heads in Ankylosing Spondylitis Requiring Staged Total Hip Arthroplasty: A Case Report of Diagnostic and Therapeutic Challenges.

Ankylosing spondylitis (AS) is a chronic immune-mediated inflammatory arthropathy primarily affecting the axial skeleton but may involve peripheral joints, particularly the hips. Avascular necrosis (AVN) of the femoral head represents a severe, underrecognized complication whose pathogenesis in AS is multifactorial-encompassing disease-intrinsic inflammatory vasculopathy, iatrogenic glucocorticoid exposure, and, potentially, a prothrombotic state. We report the case of a 28-year-old HLA-B27-positive male with a decade-long history of AS who presented with bilateral AVN of the femoral heads superimposed on secondary hip osteoarthritis, compounded by severe microcytic anemia (hemoglobin 6.5 g/dL) and a recent COVID-19 infection. The patient was initiated on infliximab (TNF inhibitor) for disease control and underwent staged bilateral total hip arthroplasty (left hip: March 2023; right hip: October 2024), achieving marked functional recovery. This case underscores the importance of prospective hip surveillance in AS, delineates the mechanistic nexus between systemic inflammation, corticosteroid use, and AVN, and highlights the perioperative considerations unique to biologic-treated AS patients. A multidisciplinary rheumatology-orthopedic approach is essential to optimize outcomes in this high-complexity population.