Total hip arthroplasty in fused hips with spine stiffness in ankylosing spondylitis

Abstract

Ankylosing spondylitis (AS) is characterized by involvement of the spine and hip joints with progressive stiffness and loss of function. Functional impairment is significant, with spine and hip involvement, and is predominantly seen in the younger age group. Total hip arthroplasty (THA) for fused hips with stiff spines in AS results in considerable improvement of mobility and function. Spine stiffness associated with AS needs evaluation before THA. Preoperative assessment with lateral spine radiographs shows loss of lumbar lordosis. Spinopelvic mobility is reduced with change in sacral slope from sitting to standing less than 10 degrees conforming to the stiff pattern. Care should be taken to reduce acetabular component anteversion at THA in these fused hips, as the posterior pelvic tilt would increase the risk of posterior impingement and anterior dislocation. Fused hips require femoral neck osteotomy, true acetabular floor identification and restoration of the hip center with horizontal and vertical offset to achieve a good functional outcome. Cementless and cemented fixation have shown comparable long-term results with the choice dependent on bone stock at THA. Risks at THA in AS include intraoperative fractures, dislocation, heterotopic ossification, among others. There is significant improvement of functional scores and quality of life following THA in these deserving young individuals with fused hips and spine stiffness.

Keywords: Ankylosing spondylitis; Total hip arthroplasty; Stiff hips; Stiff spine; Spinopelvic mobility; Functional outcome

Core Tip: Progressive spine stiffness associated with stiff hips in ankylosing spondylitis (AS) results in mobility restriction and reduces the quality of life in young individuals. Preoperative planning for total hip arthroplasty (THA) in AS requires spinopelvic mobility assessment. Sacral slope change is reduced (< 10 degrees) with a predominant stuck sitting pattern and posterior pelvic tilt. Care needs to be exercised to reduce acetabular anteversion preventing posterior impingement and anterior dislocation. Risks at THA in AS include intraoperative fractures, postop dislocation (1.9%), heterotopic ossification, among others, with revision-free survivorship of 82% at 20 years. Significant functional and mobility improvement justifies THA in AS with stiff hips and spine.