Evaluation of preoperative prediction methods for osteotomy angle of ankylosing spondylitis thoracolumbar kyphosis

English Keywords:Ankylosing spondylitis  Kyphosis  Osteotomy angle prediction

English Abstract:

  【Abstract】 Objectives: To evaluate the preoperative prediction methods of osteotomy angle of thoracolumbar kyphosis in ankylosing spondylitis(AS) patients, and to analyze their clinical values in reconstruction of spinopelvic sagittal alignment. Methods: 22 AS patients with thoracolumbar kyphosis, who underwent single segment pedicle subtraction osteotomy(PSO) from January 2015 to January 2022 in the First Affiliated Hospital of Xinjiang Medical University, were retrospectively reviewed. There were 17 males and 5 females with a mean age of 44.3±7.4 years(range, 29-56 years). Preoperative and postoperative spinopelvic parameters were measured on X-ray lateral radiographs, osteotomy angles were predicted with different methods, full balance integated index(FBI), spine femoral angle(SFA), hilus pulmonis-hip axis(HP-HA), center of both acoustic meati-hip axis(CAM-HA), and Surgimap method. And theoretical spinopelvic parameters and theoretical osteotomy angle were calculated according to pelvic incidence(PI). The differences between preoperative, final follow-up and theoretical spinopelvic parameters, and between the predictive, actual and theoretical osteotomy angles, were compared. Results: The osteotomy sites of the 22 cases included 4 in L1, 10 in L2 and 8 in L3. All the patients achieved ideal imaging and surgical results. The differences in pelvic tilt(PT), sacral slope(SS), lumbar lordosis(LL), thoracic kyphosis(TK), thoracolumbar kyphosis(TLK), global kyphosis(GK), and sagittal vertical axis(SVA) between final follow-up and preoperation were statistically significant(P<0.05). The osteotomy angles predicted with FBI, SFA, HP-HA, CAM-HA, and Surgimap methods were 50.5°±12.1°, 52.0°±11.3°, 53.9°±8.1°, 51.3°±5.8°, and 43.2°±9.2°, respectively, with statistically significant differences(F=2.342，P=0.046). The theoretical osteotomy angle required by simulated osteotomy to restore the ideal spinopelvic sagittal alignment was 51.2°±8.1°, which wasn′t statistically different from the osteotomy angles predicted with FBI, SFA, HP-HA or CAM-HA methods(P>0.05). The actual osteotomy angle during the operation was 41.1°±5.4°, which was statistically different from the osteotomy angles predicted with FBI, SFA, HP-HA and CAM-HA methods(P<0.05), but not statistically different with the angle predicted with Surgimap method(P>0.05). Conclusions: The osteotomy angles predicted with FBI, SFA, HP-HA, and CAM-HA methods are similar with the theoretical osteotomy angle, while different from the actual osteotomy angle to some extent; The osteotomy angle predicted with Surgimap method is similar with the actual osteotomy angle.