The bulbocaverosus reflex is a polysynaptic reflex that is useful in testing for spinal shock and gaining information about the state of spinal cord injuries (SCI). The test involves monitoring [anal sphincter] contraction in response to squeezing the (head) glans penis or tugging on the on an indwelling Foley catheter. The reflex is spinal mediated and involves S1-S3. The absence of the reflex without S trauma indicates spinal shock. Typically this is one of the first reflexes to return after spinal shock. Lack of motor and sensory function after the reflex has returned indicates complete SCI. Absence of this reflex in instances where spinal shock is not suspected could indicate a lesion or injury of the conus medullaris or sacral nerve roots.
This reflex can also be tested electrphysiologically, by stimulating penis or vulva and recording from the anal sphincter. This test modality is used in intraoperative neurophysiology monitoring [link] to verify function of sensory and motor sacral roots as well as the conus medullaris. See "Intraoperative Neurophysiological Monitoring of the SacralNervous System", David B. Vodusek and Vedran Deletis, in Neurophysiology in Neurosurgery, a Modern Intraoperative Approach, Vedran Deletis and Jay L. Shils, Academic Press 2002 153-165.