Evaluating a 6.0-mm candidate warning level for intraoperative L5 nerve root retraction distance during posterior lumbar interbody fusion: a retrospective cohort study

Background Postoperative radiculitis secondary to excessive L5 nerve root retraction is a debilitating complication of posterior lumbar interbody fusion (PLIF). Despite its clinical prevalence, surgeons lack a standardized, visual safety threshold, often relying on intraoperative experience and tactile feedback. This study utilized maximum physical retraction distance as a practical but incomplete proxy for mechanical nerve stress to explore a potential risk threshold and evaluate its mid-term clinical impact. Methods In this retrospective cohort study, we analyzed 80 patients who underwent PLIF. All procedures were performed using a standardized technique to ensure consistency. The maximum intraoperative transverse retraction distance of the L5 nerve root was recorded. The primary endpoint was the development of postoperative radiculitis. The optimal diagnostic cutoff was determined via receiver operating characteristic (ROC) analysis. A Cochran-Armitage test assessed the dose-response relationship, and 6-month visual analog scale (VAS), Oswestry Disability Index (ODI), and reintervention rates were evaluated. Results Postoperative radiculitis developed in 18 of 80 patients (22.5%). Multivariable regression confirmed maximum retraction distance as a robust independent predictor. ROC analysis established a 6.0 mm diagnostic cutoff (AUC = 0.678, P = 0.010; Negative Predictive Value = 87.2%). Retraction > 6.0 mm almost tripled the radiculitis rate compared to ≤ 6.0 mm (36.4% vs. 12.8%; RR = 2.85, 95% CI: 1.19–6.82, P = 0.013), yielding a massive population attributable risk (PAR) of 43.3%. Furthermore, the injury risk escalated linearly with wider displacement ( P = 0.011). By 6 months, affected patients exhibited significantly worse VAS and ODI scores ( P < 0.01, Cohen’s d > 0.8), necessitating substantially more additional interventions (RR = 2.76) and reoperations (RR = 3.44). Conclusions Transverse L5 nerve root retraction exceeding 6.0 mm is associated with an elevated risk of postoperative radiculitis, significantly impairing mid-term clinical outcomes. In standard surgical settings lacking real-time force-sensing equipment, restricting nerve displacement to ≤ 6.0 mm provides surgeons with a practical candidate warning level.