Surgical strategies and sequencing decisions for ankylosing spondylitis with severe hip deformity.

Background: Advanced ankylosing spondylitis (AS) may involve both the thoracolumbar spine and the hips, resulting in a complex deformity characterized by kyphosis, pelvic retroversion, and hip ankylosis. In severe cases, both pedicle subtraction osteotomy (PSO) and total hip arthroplasty (THA) may be required, but the optimal surgical sequence remains controversial. Main body: This controversy arises from the biomechanical coupling of the spine-pelvis-hip complex. Spinal correction can restore sagittal balance and alter pelvic orientation, thereby affecting the functional position of the acetabular component in THA. Conversely, severe hip ankylosis and contracture may compromise patient positioning, acetabular exposure, and even the feasibility of spinal correction. This review summarizes the biomechanical rationale, clinical indications, advantages, and limitations of spine-first and hip-first strategies, and highlights that surgical sequencing should be determined according to deformity dominance, surgical feasibility, and the anticipated postoperative spinopelvic environment. Conclusions: Neither spine-first nor hip-first surgery is universally appropriate for patients with AS and severe hip deformity. Surgical sequencing should be individualized through comprehensive assessment of spinal deformity, pelvic compensation, hip pathology, and expected changes in spinopelvic alignment after reconstruction.