Bilateral Posterior Tibial Nerve Research Articles

Bit-mapped imaging of somatosensory evoked potentials after stimulation of the posterior tibial nerves and dorsal nerve of the penis / clitoris

Somatosensory evoked potentials (SEPs) to unilateral or bilateral posterior tibial nerve (PTN) stimulation and to stimulation of the dorsal nerve (DN) of the penis / clitoris were recorded on 32 channels in 10 volunteers. SEPs to unilateral PTN stimulation consisted of the classic ‘W’ complex P38-N45-P56-N75 maximal on the ipsilateral central and parietal leads, and two negative waves, N33 and N37, maximal on the contralateral post- and prerolandic areas, respectively. A lemniscal P30 was also recorded. Bilateral PTN stimulation caused, by algebraic summation, the disappearance of both N33 and N37; the W complex was symmetrical and the amplitude of P30 increased. The SEPs to DN stimulation were also symmetrical, and N33 and N37 were absent. These features can be explained by the bilateral character of DN stimulation. They also differed from bilateral PTN SEPs in 3 respects; the absence of P30, the small amplitude and the weaker gradients of field distribution of the ‘W’ complex, and the somewhat different distribution of penile from clitoral or bilateral PTN, N45 and P56. These differences can be explained both by physiological (the different fiber composition of the DN) and anatomical (the deeper localization of the DN cortical receiving area) mechanisms.

Intraoperative spinal somatosensory evoked potential monitoring

The relationship of intraoperative monitoring of spinal cord somatosensory evoked potentials and postoperative deficit in 220 cases (121 with scoliosis, 41 with neoplasms, and 58 others) is reported. Bilateral posterior tibial nerve stimulation was used in 181 cases and unilateral median nerve stimulation in 39. Spinal cord (interspinous ligament needles), subcortical (neck surface), and cortical (scalp surface) SEP's were monitored. Seven patients had worsening of neurological function after surgery, three of whom demonstrated significant changes in SEP's monitored. In an additional four cases, there was more than a 50% decrease in amplitude of subcortical/cortical SEP's during monitoring, but no change in neurological status postoperatively. Combined monitoring of spinal cord, subcortical, and cortical SEP's enhanced the certainty of detecting spinal cord dysfunction even though there was a significant number of false-negative and false-positive results. A marked change in the SEP's indicated a high chance of developing a neurological deficit (three or 43% of seven cases), and if there was no change the chance of any neurological postoperative deficit was extremely low (four or 1.87% of 213 cases). These data justify the use of intraoperative SEP monitoring.