A Short Report Comparing Outcomes Between L4/L5 and L5/S1 Single-level Discectomy Surgery

Study Design: Prospective cohort study. Objective: To assess whether there is a difference in outcome between single-level discectomy at L4/L5 and L5/S1. Summary of Background Data: There is sound biomechanical reasoning to suspect a difference between spinal levels. The L4/L5 disc is more susceptible to axial torsion and is the most common site of lumbar instability. The L5/S1 motion segment is protected from torsional strain by extensive iliolumbar ligaments but is more exposed to axial compressive forces. The available literature does not include studies with preoperative standard outcome measures. Methods: Prospectively gathered data from a single center. The outcome measures were the Oswestry disability index, subjective walking distance, modified somatic perception, modified Zung depression index, low back outcome score, and visual analog score. Comparisons between L4/L5 and L5/S1 levels were made with these outcome measures using the Student t test. Results: Seventy-seven L5/S1 and 53 L4/L5 discectomies were performed. There were no clinically significant differences. Preoperative walking distance for L5/S1 patients was longer than at L4/L5 (455 m vs. 278 m; P = 0.027). At 6 months a difference also exists with the low back outcome score [47.11 (L4/L5) vs. 39.47 (L5/S1); P = 0.0229]. After 12 months at L5/S1, men had a better Oswestry disability index score than women (17% vs. 32%; P = 0.038). Across all other parameters, no significant difference was found to exist between the 2 groups. There was no difference in the recurrence rate or reoperation rate. Conclusions: This is the first study comparing a discectomy outcome at L4/L5 and L5/S1 with complete preoperative data. No significant difference exists between the 2 levels in terms of postoperative outcome. Surgical procedures such as fusion or arthroplasty should not be carried out synchronous with primary discectomy for radiculopathy. The lack of a difference between L4/L5 and L5/S1 reinforces the fact that the mechanical environment does not affect outcome and should not influence treatment.