Factors predisposing to limited flexion after total hip arthroplasty for the treatment of axial spondyloarthritis.

Hip involvement is a common condition in about one-third of patients with axial spondyloarthritis (axSpA). We assessed the incidence of possible factors that predispose patients to limited flexion after total hip arthroplasty (THA) for the treatment of axSpA. We retrospectively reviewed 516 patients with axSpA (759 hips) who underwent THA. Baseline patient demographics and clinical, laboratory, and surgery-related parameters were retrospectively collected. The preoperative and latest follow-up Harris hip score (HHS) and hip flexion ability were compared. After documenting the degree of postoperative hip flexion at the latest follow-up visit, we classified hips into good flexion group (> 90°) and poor flexion group (≤ 90°). The differences of baseline parameters between good flexion and poor flexion group were examined. Then those baseline parameters with P < 0.1 in intergroup comparisons were further included into the multivariate logistic models. The median duration of follow-up was 118.5 months (range, 25.0-269.1 months). The median HHS increased from 36.0 (25.0, 44.0) before surgery to 85.0 (77.0, 92.0) at the latest follow-up visit (P < 0.001). At the latest follow-up visit, 406 hips (53.5%) had hip flexion > 90°. The patients who were somewhat dissatisfied represented 147 hips (19.4%), and those who were very dissatisfied represented 46 hips (6.1%). The primary cause of dissatisfaction was limited range of motion (ROM) (323 hips, 80.1%). The multivariate logistic regression model revealed that the significant variables for postoperative poor hip flexion were the younger age of disease onset (OR = 0.967; P = 0.024), psoriasis (PSO) (OR = 2.071; P = 0.007), elevated C-reactive protein (CRP) (OR = 1.031; P < 0.001), and the lack of direct anterior approach (DAA) (OR = 0.372; P = 0.015). Although THA reconstruction for axSpA patients with end-stage hip involvement achieved encouraging clinical outcomes, it was prone to a restriction of hip flexion, which is closely associated with patient satisfaction. The younger age of disease onset, PSO, elevated CRP and the lack of DAA were significantly associated with limited postoperative hip flexion. Key Points • The restriction of hip flexion after THA reconstruction for axSpA patients is closely associated with patient satisfaction. • The younger age of disease onset, PSO, elevated CRP and the lack of DAA were significantly associated with limited postoperative hip flexion.