Postoperative quality of life in patients with ankylosing spondylitis and thoracolumbar kyphosis: risk factors and personalized sagittal reconstruction strategy

OBJECTIVE The aim of this study was to investigate the factors affecting postoperative quality of life in patients with ankylosing spondylitis (AS) and thoracolumbar kyphosis (TLK), and establish a personalized sagittal reconstruction strategy. METHODS Patients with AS and TLK who underwent pedicle subtraction osteotomy (PSO) from February 2009 to May 2019 were retrospectively included. Quality of life and spinal sagittal radiographic parameters were collected before surgery and at the last follow-up. Patients were divided into two groups based on the attainment of minimal clinically important difference (MCID) on the Bath Ankylosing Spondylitis Functional Index and Oswestry Disability Index. Comparisons of radiographic parameters and clinical outcomes were conducted between and within groups. Regression analysis was used to identify the risk factors within the missing MCID cohort. Sagittal reconstruction equations were established using the pelvic incidence (PI) and thoracic inlet angle (TIA) in the reached MCID cohort. RESULTS The study comprised 82 participants. Significant improvements were observed in most radiographic parameters and all quality-of-life indicators during the final follow-up compared with the preoperative measures (p < 0.05). Factors including cervical lordosis (CL) >= 18 degrees (OR 9.75, 95% CI 2.26-58.01, p = 0.005), chin-brow vertical angle (CBVA) >= 25 degrees (OR 14.7, 95% CI 3.29-91.21, p = 0.001), and pelvic tilt (PT) >= 33 degrees (OR 21.77, 95% CI 5.92-103.44, p < 0.001) independently correlated with a failure to attain MCID (p < 0.05). Sagittal realignment targets were constructed as follows: sacral slope (SS) = 0.84 PI - 17.4 degrees (R-2 = 0.81, p < 0.001), thoracic kyphosis (TK) = 0.51 PI + 10.8 degrees (R-2 = 0.46, p = 0.002), neck tilt (NT) = 0.52 TIA - 5.8 degrees (R-2 = 0.49, p < 0.001), and T1 slope (T1S) = 0.48 TIA + 5.8 degrees (R-2 = 0.45, p = 0.002). CONCLUSIONS PSO proved efficacious in treating AS complicated by TLK, yielding favorable outcomes. CBVA >= 25 degrees, CL >= 1 degrees, and PT >= 33 degrees were the primary factors affecting postoperative quality of life in patients with AS. The personalized sagittal reconstruction strategy in this study focused on the subjective sensations and daily needs of patients with AS, which were delineated by the equations SS = 0.84 PI - 17.4 degrees, TK = 0.51 PI + 10.8 degrees, NT = 0.52 TIA - 5.8 degrees, and T1S = 0.48 TIA + 5.8 degrees.