Does solid fusion eliminate rod fracture after pedicle subtraction osteotomy in ankylosing spondylitis-related thoracolumbar kyphosis?

• Published in: The spine journal 2019-01, Vol.19 (1), p.79-86
• Main Authors: Zhao, Shi-zhou, Qian, Bang-ping, Qiao, Mu, Jiang, Jun, Qiu, Yong
• Format: Article
• Language: English
• Subjects: Adult; Ankylosing spondylitis; Bone union; Female; Humans; Internal Fixators - adverse effects; Kyphosis - complications; Kyphosis - surgery; Lumbosacral Region - surgery; Male; Middle Aged; Osteotomy - adverse effects; Osteotomy - instrumentation; Pedicle subtraction osteotomy; Postoperative Complications - epidemiology; Postoperative Complications - etiology; Prosthesis Failure - adverse effects; Reoperation - statistics & numerical data; Risk factors; Rod fracture; Spinal Fusion - adverse effects; Spinal Fusion - instrumentation; Spondylitis, Ankylosing - complications; Spondylitis, Ankylosing - surgery; Thoracolumbar kyphosis
• ISSN: 1529-9430; 1878-1632
• DOI: 10.1016/j.spinee.2018.05.024

Rod fracture (RF) has a negative impact on the surgical outcome of patients with ankylosing spondylitis (AS) after lumbar pedicle subtraction osteotomy (PSO). However, there is a paucity of published studies analyzing the risk factors for RF in PSO-treated patients with AS with thoracolumbar kyphosis. The objective of this study was to investigate the risk factors for RF after PSO for thoracolumbar kyphosis secondary to AS. This is a retrospective single-center study. Patients with AS who underwent PSO for thoracolumbar kyphosis between January 2002 and December 2016 were included. Demographic data, including age, sex, body mass index, and smoking status, were summarized. The surgical data analyzed included the levels of osteotomy, the fusion levels, the upper instrumented vertebra, the lower instrumented vertebra, the osteotomy site, the rod material, the rod diameter, and the rod contour angle (RCA). Radiographic parameters included the sagittal vertical axis, thoracic kyphosis, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence. Radiographic parameters were measured at baseline, immediately after the operation, and at the final follow-up. Adequate ossification of the anterior longitudinal ligament (ALL) at the PSO level was defined by a total bony bridge. Adequate ossification of the ALL was also measured at baseline, immediately after the operation, and at the final follow-up. Patients with a minimum of 2 years' follow-up or patients who developed RF were enrolled in the study. Recruited patients were divided into the RF group and the no-RF group based on whether they developed RF. Patient demographics, operative data, radiographic parameters, and adequate ossification of the ALL were analyzed to determine the risk factors for RF. For patients with RF, the fusion status at the PSO level, the time course to the development of RF, the site of RF, and the corresponding solution were also recorded. Rod fracture occurred in 11 (8.9%) of the 123 recruited patients. Solid fusion at the PSO level was found in all patients in the RF group. The average duration to the onset of RF was 31.4 months (range, 12–68 months). All RFs occurred at or immediately adjacent to the PSO level. The RCA was greater in the RF group than in the no-RF group (27.8° vs 22.9°, p=.031). A greater proportion of patients with a rod diameter of 5.50 mm were found in the RF group than in the no-RF group (100.0% vs 68.8%, p=.033). There was a larger proportion of patients with