Association between ligamentous stenosis at spondylolisthetic segments before fusion surgery and symptomatic adjacent canal stenosis at follow-up in patients with degenerative spondylolisthesis

Study Design: A retrospective case-control propensity score-matching study.Purpose: This study aimed to longitudinally evaluate whether preoperative ligamentous stenosis at the spondylolisthetic segments could affect the incidence of symptomatic adjacent canal stenosis following one-segment fusion surgery.Overview of Literature: Several risk factors for symptomatic adjacent canal stenosis following fusion surgery have been assessed. Patients with lumbar canal stenosis mainly due to ligamentum flavum (LF) hypertrophy (ligamentous stenosis) also have LF hypertrophy in other segments.Methods: In total, 76 patients participated in this case-control study (neurologically symptomatic adjacent canal stenosis, n=33; neurologically asymptomatic cases at follow-up, n=43). Their risk factors during surgery and magnetic resonance (MR) images before the surgery and at follow-up were evaluated. Data from the two groups (n=25 each) were matched using propensity scores for age, sex, time to MR imaging at follow-up, surgical procedure, and LF hypertrophy in adjacent segments before the surgery and analyzed.Results: Compared with the asymptomatic group, the symptomatic adjacent canal stenosis group had a significantly larger LF area/spinal canal area in the spondylolisthetic segments before the surgery. During the follow-up periods (in months), they had a larger LF area/ spinal canal area in the adjacent segments: the two values were significantly correlated. The sensitivity, specificity, and positive and negative predictive values for determining symptomatic adjacent canal stenosis were high compared with on the cutoff value for the LF area/spinal canal area at the spondylolisthetic segments before the surgery. These results were the same after matching.Conclusions: Symptomatic adjacent canal stenosis is mainly caused by LF hypertrophy. Ligamentous stenosis at the spondylolisthetic segments before fusion surgery might be strongly associated with symptomatic adjacent canal stenosis at follow-up.