Loss of Correction in the Treatment of Thoracolumbar Kyphosis Secondary to Ankylosing Spondylitis A Comparison Between Smith-Petersen Osteotomies and Pedicle Subtraction Osteotomy

Study Design: Retrospective comparison of database patients. Objective: To evaluate the difference of loss of correction between Smith-Petersen osteotomies (SPOs) and pedicle subtraction osteotomy (PSO) in patients with thoracolumbar kyphosis secondary to ankylosing spondylitis (AS). Summary of Background Data: SPOs and PSO are reported to be the 2 major techniques for correction of thoracolumbar kyphosis resulting from AS. Previous studies have tried to compare the indication, technical aspects, correction obtained, and complication rates between the aforementioned 2 techniques. However, reports addressing a comparison of loss of correction between SPOs and PSO are limited. Materials and Methods: On the basis of the types of osteotomies, 50 patients were divided into 2 groups: (1) SPOs group (n = 19) including 16 male and 3 female patients, with an age range from 21 to 40 years (mean 27 y). The preoperative global kyphosis (GK) ranged from 41 to 99 degrees (average 64.6 +/- 25.6 degrees); (2) PSO group (n = 31) consisted of 26 male and 5 female patients, with an age range from 22 to 54 years (mean 36 y). The preoperative GK was 50 to 96 degrees (average 73.7 +/- 23.6 degrees). Radiographic parameters including sagittal vertical axis, T12-S1 lordosis, GK, and angle of fusion levels were measured. Results: Both groups showed similar preoperative and postoperative thoracic kyphosis, lumbar lordosis, and sagittal vertical axis. The average GK was corrected to 25.5 degrees and 31.4 degrees in SPOs group and PSO group, respectively. All cases were followed for a minimum of 2 years. At the last follow-up, mean loss of correction in the fusion levels were 6.1 degrees in SPOs group and 1.3 degrees in PSO group, respectively. The difference was statistically significant (P = 0.034). Loss of correction of > 5 degrees occurred in 4 cases (21.1%) in SPOs group, and 5 cases (16.1%) in PSO group. Conclusions: Both SPOs and PSO showed similar effect in correcting the thoracolumbar kyphosis secondary to AS. However, patients treated with the SPOs technique showed higher risk in loss of correction in the instrumented region.