Reduction Capacity and Factors Affecting Slip Reduction Using Cortical Bone Trajectory Technique in Transforaminal Lumbar Interbody Fusion for Degenerative Spondylolisthesis

Introduction: Vertebral slip reduction has been recommended in arthrodesis for lumbar degenerative spondylolisthesis (LDS) to achieve balanced spinal alignment and bone fusion. However, what determines the degree of slip reduction using cortical bone trajectory technique for lumbar pedicle screw insertion is yet to be determined. Thus, in this study, we aim to investigate the slip reduction capacity using cortical bone trajectory (CBT) technique and to identify factors affecting the slip reduction rate.Methods: This is a retrospective radiological evaluation of prospectively collected patients. In total, 49 consecutive pa-tients who underwent single-level transforaminal lumbar interbody fusion for LDS using the CBT technique were included (mean follow-up: 28.9 months). Firstly, radiological parameters of fused segment including the percentage of anterior verte-bral slip (%slip), lordotic angle, and disk height were measured. Then, patient and procedure-related parameters were exam-ined to determine factors related to the slip reduction rate using multiple regression analysis.Results: The %slip was reduced from 15.0 +/- 4.8 to 1.6 +/- 2.3% immediately after surgery and 2.2 +/- 2.9% at the last follow-up (p < 0.01), with a slip reduction rate of 87.5 +/- 15.7% and correction loss of 0.6 +/- 2.1%. As per multivariate regression analy-sis, it was found that preoperative %slip (standardized regression coefficient [beta]=-0.55, p=0.003) and the depth of screw insertion in the caudal vertebra (beta=0.38, p=0.03) were significant independent factors affecting slip reduction rate (adjusted R2 =0.29, p=0.008). Conclusions: To the best of our knowledge, this study is the first to investigate the capacity for and factors affecting slip reduction using the CBT technique for LDS. The CBT technique may be a useful option for achieving slip reduction, and the depth of screw insertion in the caudal vertebra was identified as a significant technical factor to obtain a more signifi-cant reduction of slipped vertebra.