Radiologic and clinical outcomes comparison between single- and two-level pedicle subtraction osteotomies in correcting ankylosing spondylitis kyphosis

Background contextSingle pedicle subtraction osteotomy (PSO) has been used to correct ankylosing spondylitis (AS) kyphosis successfully, but this approach seems insufficient to correct severe kyphosis. Two-level PSO has been attempted to correct advanced kyphosis in recent years. However, studies have not yet compared outcomes between single and double PSOs, and the indications to perform two-level PSO are unclear.PurposeThis study aimed to compare the radiologic and clinical outcomes between single- and two-level PSOs in correcting AS kyphosis.Study designThis work is a retrospective cohort study.Patient sampleSixty patients were included. Thirty-seven underwent single-level PSO, and 23 underwent one stage two-level PSO.Outcome measuresThe radiologic analysis included thoracic kyphosis, thoracolumbar junction, lumbar lordosis, pelvic index, chin-brow vertical angle (CBVA), sagittal vertical axis (SVA), and pelvic tilt (PT). Clinical assessment was performed with a Scoliosis Research Society-22 (SRS-22) outcomes instrument. The operative time, blood loss, and complications were also documented.MethodsAll of the aforementioned measurements were recorded before surgery, after surgery, and at the last follow-up. The outcomes were compared between the two groups.ResultsThe operating time was 232±52 minutes for single- and 282±43 minutes for two-level PSOs. The blood loss was 1,240±542 mL (Level 1) and 2,202±737 mL (Level 2). The total spine correction was 43.2°±15.1° (Level 1) and 60.6°±19.1° (Level 2) (p<.001), the SVA correction was 13.2±10.6 cm (Level 1) and 23.6±10.2 cm (Level 2) (p<.001), and the PT correction was 10.1°±11.6° (Level 1) and 15.2°±10.8° (Level 2) (p<.001). The CBVA correction was 50.6°±17.8° (Level 1) and 51.4°±18.6° in (Level 2) (p>.05). All patients could walk with horizontal vision and lie on their backs postoperatively. The SRS-22 improved from 1.7±0.4 to 4.2±0.8 in the two-level group and 1.8±0.8 to 4.3±0.7 in the single-level group. The fusion of the osteotomy was achieved in each patient. The complications were similar in both groups.ConclusionsPedicle subtraction osteotomy is an effective method to correct kyphosis with AS. Most patients can be successfully treated by single PSO. In severe patients, two-level PSO may be preferable because its correction ability is greater and spine curvature is better than that of single-level PSO. However, two-level PSO requires an increased operating time and results in increased blood loss. Nevertheless, the complications were similar between the two groups.