Correlations of the mechanical complications following pedicle subtraction osteotomy in ankylosing spondylitis related-thoracolumbar kyphosis with global alignment and proportion score and analysis of its risk factors

English Keywords:Ankylosing spondylitis  Thoracolumbar kyphosis  Global alignment and proportion  Pedicle subtraction osteotomy  Mechanical complication

English Abstract:

  【Abstract】 Objectives: To investigate the correlations between the mechanical complications after pedicle subtraction osteotomy(PSO) in ankylosing spondylitis(AS) patients with thoracolumbar kyphosis and global alignment and proportion(GAP) score and analyze the risk factors for such mechanical complications. Methods: AS patients with thoracolumbar kyphosis who underwent single-level PSO between January 2010 and June 2019 and were followed up for 2 years and above were analyzed retrospectively. Radiographic parameters including sagittal vertical axis(SVA), pelvic incidence(PI), sacral slope(SS), lumbar lordosis(LL), lower lumbar lordosis(LLL), and global tilt(GT) were measured on lateral full-spine X-rays preoperatively and postoperatively to calculate the GAP score. The patients were divided into 3 groups: proportion group(GAP score 0-2), moderate disproportion group(GAP score 3-6), and severe disproportion group(GAP score 7-13). All the mechanical complications during follow-up were documented including proximal junctional kyphosis/failure(PJK/PJF), distal junctional kyphosis/failure(DJK/DJF), and rod fracture, and the incidences of the mechanical complications were compared between the 3 groups. The age, gender, fusion levels, classification of kyphosis, bone mineral density(BMD), body mass index(BMI), and the level of osteotomy were also collected. Univariate analysis and multivariate logistic regression analysis were used to determine the risk factors for mechanical complications in AS patients following PSO. Results: 163 patients were included, including 145 males and 18 females, with a mean age of 35.8±10.0 years(range, 17 to 63 years) and the follow-up period was 38.6±16.9 months. A total of 26 patients had mechanical complications during follow-up containing rod fracture(n=16) and PJK(n=10). The incidences were 19.2%(5/26), 16.1%(9/56) and 14.8%(12/81) in proportion group, moderate disproportion group and severe disproportion group, respectively( χ2=0.287, P=0.866). Univariate analysis showed that age(P=0.036) and BMI(P<0.001) were associated with postoperative mechanical complications. Multivariate logistic regression analysis showed that age(P=0.046) and BMI(P<0.001) were the independent risk factor for mechanical complications in AS patients with thoracolumbar kyphosis following PSO. Conclusions: The mechanical complications following PSO in AS patients with thoracolumbar kyphosis have no obvious correlations with GAP score, while they were correlated with age and BMI.