Stretch on the L5 nerve root in high-grade spondylolisthesis reduction

OBJECTIVE L5 nerve root (L5-NR) injury after surgery for high-grade spondylolisthesis (HGS) was considered a nerve stretch associated with reduction. Currently, however, no study has directly measured the stretch on the L5-NR during HGS reduction procedures. METHODS CT data of 4 patients with mild lumbar degeneration (control group [CG]) and 4 patients with HGS (spon- dylolisthesis group [SG]) were used for 3D printing to develop L5 vertebrae and sacrum models. These models were mounted on a self-designed reduction apparatus, which performed vertical translation (disc heights of 0, 5, and 10 mm), anterior-posterior translation (reduction, 0%-100%), and slip-angle correction (0 degrees to -30 degrees). The L5-NR was simulated by using a rabbit sciatic nerve. The cephalic side of the nerve was fixed at the upper base of the L5 pedicle, while the caudal side was connected to a high-precision sensor and an indicator to measure the tension (stretch) on the nerve during the reduction procedures in real time. RESULTS The SG had shorter L5-NRs than the CG. At a 0-mm disc height, the peak tension on the L5-NR changed from 0 N (reduction 0%) to 1.81 +/- 0.54 N (reduction 100%) in the SG and to 1.78 +/- 0.71 N in the CG. At a 10-mm disc height, the tension changed from 1.50 +/- 0.67 N to 4.97 +/- 1.04 N in the SG and from 0.92 +/- 0.45 N to 3.26 +/- 0.88 N in the CG. In both the CG and SG, at the same disc height, all values from the complete reduction process were statistical- ly significant. Furthermore, at the same degree of reduction, the comparisons between different disc heights were almost all statistically significant. Intergroup comparisons showed that an increased disc height would cause more tension on the L5-NR in the SG than in the CG. At a 10-mm disc height, all results between the groups demonstrated statistical significance. The slip-angle correction produced a slight increase in the tension on the L5-NR in both groups. CONCLUSIONS Increased disc height and reduction significantly increased the tension on the L5-NR, which demon- strated a nonlinear curve. The slip-angle correction from 0 degrees to -30 degrees slightly increased the tension on the L5-NR. Under the same degree of reduction and restored disc height, the SG had more tension on the L5-NR than the CG.