Risk factors of adjacent-segment disease after short-segment fusion in patients with de novo degenerative lumbar scoliosis

OBJECTIVE Short-segment fusion (SSF) is an effective surgical option for appropriately selected patients with de novo degenerative lumbar scoliosis (DNDLS). Considering that DNDLS is frequently accompanied by multisegment degeneration and potential instability across the entire lumbar segments, it is inevitable that unhealthy segments remain after SSF, thereby increasing the potential risk of adjacent-segment disease (ASD) occurrence. Therefore, the authors aimed to identify the risk factors for ASD in patients with DNDLS who underwent SSF. METHODS This retrospective study included 80 patients with DNDLS (Cobb angle > 10 degrees) who underwent SSF (1 or 2 levels) between December 2010 and July 2018 with a minimum follow-up duration of 5 years. The participants were divided into two groups: ASD and non-ASD. ASD was defined as clinical ASD rather than radiographic ASD. Various patient and operative variables were compared between the groups. Global and regional radiographic parameters (preoperatively and postoperatively) were also compared between the two groups using plain radiography and MRI. Consequently, univariate and multivariate analyses were conducted to identify the risk factors for ASD occurrence. The receiver operating characteristic (ROC) curve was used to calculate the cutoff values. RESULTS The mean +/- SD age was 67.7 +/- 7.2 years at the time of SSF, and there were 62 women (77.5%) enrolled in the study. Thirty patients (37.5%) were in the ASD group and 50 patients (62.5%) were in the non-ASD group. The mean time from the surgery to ASD diagnosis was 34.9 +/- 28.2 months in ASD group. Thirteen patients required revision surgery at a mean time of 8.8 +/- 7.0 months after ASD occurrence. Multivariate logistic regression analysis demonstrated that preoperative disc wedging angle (OR 1.806, 95% CI 1.255-2.598, p = 0.001), presence of facet tropism (defined as z 10 degrees difference between the facet joint angles of the right and left sides) (OR 5.534, 95% CI 1.528-20.040, p = 0.009), and foraminal stenosis z grade 2 (OR 5.935, 95% CI 1.253-28.117, p = 0.025) were significant risk factors for ASD development. The cutoff value of the preoperative disc wedging angle was calculated to be 2.5 degrees using the ROC curve. CONCLUSIONS Preoperative disc wedging angle z 2.5 degrees, presence of facet tropism, and foraminal stenosis z grade 2 were identified as significant risk factors for ASD development after SSF in patients with DNDLS.