Hip Replacement in Ankylosing Spondylitis Patients with Advanced Hip Involvement: Factors Associated with Bilateral Total Hip Arthroplasty.

Bilateral THA is more common in AS patients with advanced hip involvement. Bilateral onset in hips, a BASRI-hip score of 4, and a higher level of ESR are risk factors associated with bilateral THA, while anti-TNF therapy is a protective factor reducing the progression of hip involvement to bilateral THA.