The Intersegmental Pudendal Reflex: Evidence of human sacral-to-thoracolumbar connectivity for intraoperative monitoring.

OBJECTIVE

To introduce the Intersegmental Pudendal Reflex (IPR) and evaluate its potential as a surrogate functional marker for S2-S4 integrity and for extended suprasegmental levels during Intraoperative Neurophysiological Monitoring (IOM).

METHODS

Observational retrospective study involving twenty patients undergoing spinal surgery. Pudendal nerve stimulation elicited sacral and suprasacral responses. Reflexive responses were recorded simultaneously in the external anal sphincter (bulbocavernosus reflex, BCR) and the abdominal oblique muscles (IPR).

RESULTS

The IPR consists of a short-latency R1 of 31.7 ± 7.5 ms (mean ± standard deviation, milliseconds) and a highly variable long-latency R2 of 124.5 ± 40 ms. The IPR provides additional confirmation of sacral integrity (S2-S4) but, critically, its output to higher segments demonstrates an extensively polysynaptic connection extending cranially to the upper lumbar and lower thoracic spinal cord.

CONCLUSIONS

The IPR is a reproducible, intersegmental somatic pudendal reflex in anesthetized humans. It enhances standard IOM by confirming sacral integrity along BCR, while simultaneously assessing the functional status of pathways that ascend intersegmental spinal levels.

SIGNIFICANCE: The IPR enhances standard IOM by confirming sacral integrity and extending monitoring cranially. Its polysynaptic conduction provides a physiological framework to explore the assessment of spinal cord central pattern generators in future clinical studies on micturition, sexual function, and locomotion, a new and critical area of research for IOM.