RATIONALE Ankylosing spondylitis (AS) can affect the hip joint, causing deformity and disability. Total hip arthroplasty can obviously relieve the pain of the hip joint, and reconstruct the function of hip joint. Epidural anesthesia in this patient population has high risk of epidural hematoma, but the reason is unclear. PATIENT CONCERNS A 44-year-old man diagnosed with AS underwent total hip...