Lateral Lumbar Interbody Fusion: An Update on Motor Deficits in 1000 Patients Across Two Decades

Study Design Retrospective cohort study. Objective To provide updated rates for approach-related postoperative motor deficits following lateral lumbar interbody fusion (LLIF) and identify risk factors. Methods 1000 stand-alone LLIF procedures between 2006 and 2024 were reviewed and divided into the first decade (2006-2015, n = 395) and the second decade (2016-2024, n = 605). Electronic records were screened for iliopsoas and quadriceps deficits preoperatively and postoperatively (at discharge, 6 weeks, 3 months, 6 months, 1 year, and last follow-up) defined as a decline in MRC strength grades relative to baseline. Results The incidence of postoperative ≥1 MRC grade iliopsoas deficits declined from 12.7% to 4.1% and quadriceps deficits from 5.3% to 1.7% at 6 weeks ( P < 0.001 and P = 0.002, respectively). In the second decade, persistent iliopsoas or quadriceps weakness was observed in 0.8% and 0.5% (n = 3) of patients at 6 months and 1 year, respectively. At 2 years, only 1 of 605 patients had residual ≥1 MRC grade quadriceps weakness, and no patient had persistent iliopsoas weakness. Independent predictors of deficits were surgery at L4/5 (iliopsoas: OR 2.2, 95% CI 1.1-4.5; quadriceps: OR 5.9, 95% CI 1.3-26.5) and operative time [per hour] (iliopsoas: OR 1.4, 95% CI 1.2-1.6; quadriceps: OR 1.4, 95% CI 1.1-1.7). Conclusions Rates of postoperative motor deficits after standalone LLIF have improved significantly over the past decade. Increased surgical time and surgery at L4/5 remain key risk factors, but most deficits are transient. LLIF at L4/5 can be considered safe in appropriately selected patients.