Preliminary observations on neuromuscular pathways of the lower extremities: findings from intraoperative nerve root...

The segmental innervation patterns of lower extremity muscles remain poorly defined, despite their critical importance in both clinical diagnosis and surgical planning for lumbar spinal conditions. Variability in these patterns, particularly under chronic nerve root compression, complicates the development of accurate diagnostic and therapeutic strategies. This study aimed to elucidate the segmental innervation patterns of lower extremity muscles through intraoperative nerve root stimulation during lumbar spinal surgery combined with motor evoked potential (MEP) during lumbar spinal surgery. A total of 30 patients diagnosed with unilateral nerve root impairment due to degenerative lumbar canal stenosis were enrolled in this study. All patients provided informed consent, demonstrated lower extremity muscle strength graded 4 or higher on the manual muscle test, and were scheduled for surgeries that enabled direct visualization of bilateral nerve roots. During the surgical procedures, 128 lumbosacral nerve roots (L2-S1) were stimulated using a monopolar stimulator, and MEPs were recorded from key lower extremity muscles, including the vastus lateralis, tibialis anterior, and medial gastrocnemius. The vastus lateralis muscle was consistently innervated by the L2 root in 100% of cases, confirming a stable and reproducible pattern. In contrast, stimulation of the L5 root revealed notable anomalies in 8% of cases, where compensatory mechanisms or anatomical anomalies appeared to alter the expected innervation patterns. Furthermore, differences in muscle innervation between the left and right sides were observed in 39% of tested nerve roots, with variability being particularly pronounced in lower lumbar levels, such as L4, L5, and S1.