The “20-minute Rule” in Lateral Lumbar Interbody Fusion. Fact or Fiction? A Multi-Center Analysis of 658 Patients

Study Design Retrospective Cohort Study. Objective Lateral lumbar interbody fusion (LLIF) is a treatment option for correcting lumbar degenerative pathologies that uses a retroperitoneal, transpsoas corridor to the disc space. Conventional teaching of the LLIF technique has been to perform the procedure ‘as efficiently as possible', with a goal of keeping the total retractor time to less than 20 minutes to prevent injuries. This study aims to examine the sensitivity of the “20-minute” rule for predicting postoperative femoral nerve palsy. Methods A multicenter, retrospective cohort of patients who underwent an LLIF was established. Retractor time was recorded and compared to postoperative motor exams for its relationship to motor injury. Results 658 total patients were included in the study. The most frequently operated level was L4-5 (71.7%). The average retractor time was 17.5 ± 8.0 minutes. The injury rate of the cohort was 1.8% (12/658). There was no difference in average retractor time for non-injured vs injured patients (17.5 ± 8.0 min vs 19.6 ± 11.2 min, P = 0.367). Analysis of the “20-minute” rule for LLIF revealed a sensitivity of 50%, a specificity of 73.8%, and a positive predictive value of 3.4%. There were 174 patients with retractor times >20 minutes and six injuries, yielding a false positive rate of 96.6%. Conclusion Post-operative quadriceps motor palsy after lateral lumbar interbody fusion does not appear to be caused by prolonged retractor time greater than 20 minutes. The authors recommend surgical efficiency without the need to rush through the procedure because the “20-Minute” threshold is approaching. Limiting retractor time to under 20 minutes was a poor predictor of post-operative quadriceps injury.