Expanded question: Has any study examined the importance of proper positioning of needle electrodes in the anal sphincter to obtain the bulbocavernosus reflex?

Answered on February 6, 2025
The importance of proper positioning of needle electrodes in the anal sphincter for obtaining the bulbocavernosus reflex (BCR) has been examined in the medical literature. The study by Rodi and Vodusek highlights that controlled intramuscular placement of detecting electrodes significantly improves the detection of the BCR. Specifically, the study found that with controlled intramuscular placement, the BCR was detected in 97% of hemisphincters in men, compared to a much lower detection rate with superficial placement.[1] This underscores the critical role of precise electrode positioning in achieving reliable BCR recordings.
Additionally, Skinner and Vodušek discuss the importance of exacting recording techniques, which include proper electrode placement, to enhance the reliability and reproducibility of BCR testing. They report a high baseline BCR acquisition rate, which suggests that meticulous attention to electrode positioning is a key factor in successful intraoperative monitoring of the BCR.[2]
These findings collectively emphasize that the proper positioning of needle electrodes in the anal sphincter is crucial for the effective elicitation and recording of the BCR, particularly in intraoperative settings.

1.
Intraoperative Monitoring of the Bulbocavernosus Reflex: The Method and Its Problems.

Rodi Z, Vodusek DB.

Clinical Neurophysiology : Official Journal of the International Federation of Clinical Neurophysiology. 2001;112(5):879-83. doi:10.1016/s1388-2457(01)00500-4.

Objectives: This study evaluates the method of intraoperative neurophysiological monitoring of the bulbocavemosus reflex (BCR) with reference to stimulation and detection.

Methods: The study was performed on a group of 65 patients, 53 men and 12 women, who underwent surgery for lower thoracic and lumbar spinal trauma, with no neurological deficit prior to or following surgery. Stimulating electrodes were placed on the dorsum of the penis or the clitoris. Single and double stimuli were used, as well as trains of 3, 4 and 5 stimuli. Detecting wire electrodes were introduced into the perianal region.

Results: A single stimulus elicited the BCR in 50%, pairs in 75%, trains of 3 in 95%, and trains of 4 and 5 in 100% of patients. With placement of the detecting electrodes 2.5 cm deep to the skin, the BCR was detected in 13% of hemisphincters in women, and in 81% of hemisphincters in men. With controlled intramuscular placement of detecting electrodes, the BCR was detected in 97% of hemisphincters in men. With bifocal detection the BCR amplitudes were 30-312 mV (median 90), and interside amplitude ratio was 0.05-1 (median 0.66); with monofocal detection, amplitudes and interside amplitude ratio were 30-560 mV (median 200) and 0.15-1 (median 0.86), respectively.

Conclusions: A train of 4 electrical stimuli is optimal in eliciting the BCR in anesthetized patients. The low rate of elicitability in women was most probably due to inefficient stimulation. Detection was improved by controlled intramuscular placement of electrodes. Monofocal detection yielded higher BCR amplitudes. Interside difference and interindividual variability of the BCR amplitude were considerable.

2.
Intraoperative Recording of the Bulbocavernosus Reflex.

Skinner SA, Vodušek DB.

Journal of Clinical Neurophysiology : Official Publication of the American Electroencephalographic Society. 2014;31(4):313-22. doi:10.1097/WNP.0000000000000054.

: The bulbocavernosus reflex (BCR) is mediated by the sacral somatic afferent/efferent periphery as well as the sacral cord. Unfortunately, the reflex has suffered from a partly deserved reputation as difficult to implement. However, recent stratagems have improved the test's reliability. Multipulse stimulation (enhanced by double trains as required) and exacting recording technique can yield positive and remarkably reproducible results in patients of all ages and either sex. In this review, we document a 94% baseline BCR acquisition rate among 100 consecutive cases in one institution. Acceptance and routine use of the BCR is needed to help assure optimal post-operative low sacral function in intradural and extradural surgeries at the level of conus medullaris, cauda equina, sacral plexus, and the pudendal nerve. Case studies within this review illustrate the power of the BCR to predict patient outcome or, much more importantly, reverse incipient patient injury in real time.