Analysis of risk factors for sagittal translation after pedicle subtraction osteotomy in patients with ankylosing spondylitis

Abstract

Background Context Sagittal translation, a potential complication of pedicle subtraction osteotomy (PSO), can result in neurologic damage. However, few studies have been conducted on sagittal translation and its risk factors after PSO in patients with ankylosing spondylitis (AS).

Purpose We aimed to report cases of sagittal translation that developed after PSO in patients with AS with kyphotic deformity and to analyze risk factors for sagittal translation.

Study Design A retrospective case-control study was carried out.

Patient Sample This study included 53 patients (58 cases) with AS who underwent PSO to correct their kyphotic deformity.

Outcome Measures The modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) was measured before the surgery. Radiological pelvic and sagittal parameters were also measured before and after surgery. Developments of sagittal translation were confirmed with intraoperative radiograph.

Methods The subjects were grouped according to the presence (ST group) and absence (non-ST group) of sagittal translation. The demographic and radiological parameters were compared between two groups. Through multivariate logistic regression analysis, the correlations between sagittal translation and relevant parameters were analyzed for risk factor evaluation.

Results Sagittal translation developed in 16 patients (30.2%) [16 cases (27.6%)]. The mean lumbar lordosis angle and sagittal vertical axis of both ST group and non-ST group were successfully corrected. In a comparison of two groups, the ST group (58.2±13.3) showed a significantly higher mSASSS than the non-ST group (33.9±11.9) (p<.001). The ST group (50.4°±7.8°, 16.9°±6.8°) also showed a significantly higher preoperative pelvic incidence and sacral slope than the non-ST group (45.3°±7.2°, 11.0°±7.7°) (p=.026, p=.011). No significant differences were observed between the two groups for the rest of radiological parameters. In multivariate analysis, only mSASSS was positively correlated with sagittal translation (odds ratio 1.16, p=.001).

Conclusion The incidence of sagittal translation after PSO was closely related with severity of ankylosis in patients with AS. Therefore, surgeons must consider sagittal translation, which could induce neurologic complications, when PSO is performed for patients with AS with severe ankylosis.