The preoperative predictors for subsequent degeneration in L5-S1 disc after long fusion arthrodesis terminating at L5 in patients with adult scoliosis: focus on spinopelvic parameters

BACKGROUND: The subsequent L5-S1 disc degeneration associated with long fusion arthrodesis terminating at L5 in patients with adult scoliosis has been a common concern. However, few studies paid attention to its preoperative predictors, especially in spinopelvic parameters. The purpose of the present study was to clarify the preoperative predictors of subsequent L5-S1 disc degeneration after long fusion arthrodesis terminating at L5 in patients with adult scoliosis on spinopelvic parameters. METHODS: In this retrospective study, we enrolled 67 patients with adult scoliosis, and the patients were divided into disc degeneration group (DD) and no disc degeneration group (NDD), based on the presence or absence of subsequent L5-S1 disc degeneration. The status of L5-S1 disc was evaluated by a modified version of radiographic classification. Characteristics and spinopelvic parameters of preoperative patients were collected as potential predictors for subsequent lumbosacral disc degeneration after long fusion arthrodesis terminating at L5 in patients with adult scoliosis. Multivariate logistic regression analysis and the receiver operating characteristic curve were used to identify the preoperative predictors, with an adjusted odds ratio (OR) and 95% confidence intervals (CI). RESULTS: Thirty-six patients (53.73%) with subsequent L5-S1 disc degeneration were divided into group DD (preoperative score 0.81 ± 0.57, last follow-up score 1.83 ± 0.60, P < 0.001), and the other 31 patients were divided into group NDD (preoperative and last follow-up score 0.87 ± 0.49). There was no statistical difference in preoperative score (P = 0.583) of lumbosacral disc between two groups; however, significant statistical difference showed in last follow-up score (P < 0.001). Multivariate logistic regression identified three preoperative predictors: pelvic incidence (PI) (P = 0.018), sagittal vertical axis (SVA) (P = 0.024), and sacrum-femoral distance (SFD) (P = 0.023). PI < 48.5° (OR = 0.911, 95% CI = 0.843–0.984), SVA > 4.43 cm (OR = 1.308, 95% CI = 1.036–1.649), and SFD > 5.65 cm (OR = 1.337, 95% CI = 1.041–1.718) showed satisfied accuracy for predicting subsequent L5-S1 disc degeneration. CONCLUSION: The prevalence of the subsequent L5-S1 disc degeneration after long fusion arthrodesis terminating at L5 in patients with adult scoliosis was 57.3% (36 of 67 patients). PI < 48.5°, SVA > 4.43 cm, and SFD > 5.65 cm were preoperative predictors for the subsequent L5-S1 disc degeneration. More attention should be paid to prevent the L5-S1 disc from degeneration when these preoperative predictors exist, especially with two or more.