Pudendal mapping of S1 rootlets in a functional posterior rhizotomy: when an S1 posterior root shows a high pudendal dorsal action potential—a technical note



The standard level for lesioning in a functional posterior rhizotomy (FPR) ranges from L2 to S1/S2. Lesioning of the S1 and S2 rootlets strongly correlates with a reduction in ankle spasticity. In the Japanese population, the S2 root often shows the highest dorsal root action potentials (DAPs) in the afferent fibers of the pudendal nerve and is not lesioned to preserve postoperative urinary function. Thus, cutting of the S1 root plays a key role in reducing ankle spasticity in FPR. However, on rare occasions, even an S1 root may show high DAP in the afferent fibers of the pudendal nerve.


The present, brief, technical note aimed to describe how an S1 root with a relatively high DAP in the afferent fibers of the pudendal nerve may be handed.


In the procedure, the S1 root is divided into several rootlets, and each rootlet is tested for the pudendal mapping. A train of electrical stimuli is delivered to each rootlet in the standard FPR. If electromyography (EMG) findings after electrical stimulation are highly abnormal while the pudendal mapping demonstrates no or a relatively low DAPs, the rootlet is cut. In contrast, even if the rootlet shows highly abnormal EMG findings, it is preserved if mapping demonstrates a relatively high DAP.


The S1 pudendal mapping is combined with EMG findings to achieve satisfactory reduction in ankle spasticity while preserving urological function.

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Morota, N. Pudendal mapping of S1 rootlets in a functional posterior rhizotomy: when an S1 posterior root shows a high pudendal dorsal action potential—a technical note. Childs Nerv Syst (2020). https://doi.org/10.1007/s00381-020-04751-y

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  • Rhizotomy
  • Pudendal mapping
  • S1 root
  • Dorsal action potential
  • Intraoperative neurophysiology