Posterior lumbar interbody fusion for degenerative spondylolisthesis; slippage reduction can be a risk factor for adjacent segment disease

Purpose: Several risk factors for adjacent segment disease (ASD) after posterior lumbar interbody fusion (PLIF) have been reported. High pelvic incidence (PI) has been identified as risk factors for L4 anterior slip in cases of lumbar degenerative spondylolisthesis. Correcting the slip with L4–L5 fixation merely restores the lumbar alignment, but the PI itself remains unchanged. We hypothesized that the fused L4 vertebral body might continue to be subject to the slip-inducing force, even after fixation, and that slip correction might be a cause of ASD. The purpose of this study is to identify the risk factors for adjacent ASD following single-segment PLIF in patients with L4 spondylolisthesis, with a particular focus on the reduction of vertebral body slippage. Methods: Fifty-two patients who underwent posterior lumbar interbody fusion at the L4–L5 level for L4 degenerative spondylolisthesis were investigated. Patients were divided into two groups: the ASD group (n = 12) and the non-ASD group (n = 40). %Slip before surgery and at follow-up, Δ%Slip (Δ%Slip = %Slip before surgery—%Slip at follow-up), L4–L5 interbody height, and L4–L5 lordosis angle were evaluated. Results: Stepwise multivariate regression analysis revealed Δ%Slip to be a risk factor for ASD (odds ratio: 1.22, 95% confidence interval: 1.04–1.43, p = 0.015). In the receiver operating characteristic analysis, the cutoff value for Δ%Slip was 7.3% (sensitivity: 75.0%, specificity: 67.5%, and area under the curve = 0.725). Conclusions: Our findings suggest that the reduction of L4 slippage may contribute to the development of ASD in patients with L4 spondylolisthesis.