Prediction of lumbar lordosis index on post-operative sagittal balance during follow-up in degenerative scoliosis

English Keywords:Degenerative scoliosis  Lumbar lordosis index  Sagittal imbalance  Sagittal alignment

English Abstract:

  【Abstract】 Objectives: To evaluate the role of post-operative lumbar lordosis index(LLI) in predicting the sagittal balance in degenerative scoliosis by comparing the LLI in patients with or without sagittal balance during follow-up. Methods: This was a retrospective review on 57 patients with degenerative scoliosis who underwent one stage posterior surgical instrumentation in our spinal center from January 2005 to December 2011. The inclusion criteria included: (1) age more than 45 years; (2) follow-up more than 2 years; (3) more than 5 fusion levels. The following sagittal spino-pelvic parameters were measured: sagittal vertical axis(SVA), thoracic kyphosis(TK), lumbar lordosis(LL), pelvic incidence(PI), pelvic tilt(PT) and sacral slope(SS). Lumbar lordosis index(LLI) was also assessed as the formula: LLI=LL/PI. Based on sagittal alignment at the last follow-up, patients were divided into two groups: group A(SVA≤5cm and PT≤25°, 41 cases) and group B(SVA>5cm or PT>25°, 16 cases). Correlation was researched among radiographic parameters at each time point. Independent t test was performed for statistical analysis. For all statistical analyses, the level of significance was set at P<0.05. Results: The mean follow-up averaged 4.4±1.9 years(range: 2-8 years). No significant difference was observed regarding the follow-up time between group A and B(4.3±1.8 years for group A and 4.6±1.9 years for group B, P=0.752). Significant correlations of LLI were found with PI, LL, PT, SVA, loss of LL at the corresponding time point(all P<0.05). No correlation between TK and SS was observed. Preoperative LLI did not differ significantly between group A and B(0.45±0.18 vs. 0.47±0.21, P=0.638). Postoperative LLI was 0.89±0.13 in group A, significantly larger than that in group B(0.89±0.13 vs. 0.61±0.14, P=0.005). SVA in group A was 2.73±2.62cm at the last follow-up, significantly smaller than that in group B(2.73±2.62cm vs. 7.81±3.26cm, P<0.01). PT at the last follow-up averaged 20.34°±4.28° and 29.81°±5.13° respectively in group A and B. Conclusions: Failure to restore LLI can predispose sagittal malalignment during follow-up in patients with degenerative scoliosis. Well-restored LLI may reduce the risk of postoperative sagittal imbalance during follow-up.