Anterior Lumbar Plexus Position on Preoperative Supine MRI Is Associated With Postoperative Motor Deficits After Lateral Lumbar Interbody Fusion at L4-5.

Abstract

Study design: Retrospective propensity score-matched case-control study.

Objective: To evaluate whether preoperative MRI-based psoas morphology, lumbar plexus position, iliac crest height, and psoas cross-sectional area (CSA) are associated with postoperative motor deficits (PMDs) following standalone lateral lumbar interbody fusion (SA-LLIF) at L4-L5.

Summary of background data: PMDs remain a recognized complication of LLIF. Although anatomical characteristics have been implicated in neurological risk, the clinical value of classifying these features on preoperative MRI remains incompletely understood.

Methods: Patients who developed PMDs after L4-L5 SA-LLIF were propensity score matched to patients without PMDs. Preoperative supine MRI was used to assess operative-side psoas morphology (Amaral classification), lumbar plexus position (Moro zones), iliac crest height, and absolute and height-adjusted psoas CSA. Conditional logistic regression analyses, including a multivariable model incorporating both psoas morphology and lumbar plexus position, were performed to evaluate their associations with PMDs.

Results: A total of 172 matched patients were included. An anterior lumbar plexus position extending beyond the midpoint of the vertebral body on preoperative supine MRI (Moro Zones 1-2) remained independently associated with PMDs after adjustment for psoas morphology (OR 14.37, 95% CI 1.78-115.95; P=0.012). Although Type III psoas morphology according to the Amaral classification was associated with increased odds of PMDs in univariable analysis (OR 4.77, 95% CI 1.65-13.76; P=0.004), this association was no longer statistically significant after adjustment for lumbar plexus position (OR 2.54, 95% CI 0.90-7.18; P=0.078). Iliac crest height, psoas CSA, and height-adjusted psoas CSA were not associated with PMDs.

Conclusions: Psoas morphology and lumbar plexus position on preoperative supine MRI were associated with PMDs following L4-L5 SA-LLIF. An anterior lumbar plexus position remained independently associated with PMDs after adjustment for psoas morphology. These findings support preoperative MRI-based anatomical assessment for neurological risk stratification and patient counseling.