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Bulbocavernosus reflex -Clinical significance

It is a superficial reflex that is useful  in paraplegia.The bulbocavernosus reflex is an oligosynaptic reflex mediated through the S2–S4 spinal cord segments
Method of elicitation 
This reflex can be elicited by pinching on the glans penis or pulling on the catheter with one hand the other hand is placed over the perineum at the root of the penis

Normal Response
Normal response is the reflex contraction of the bulbospongiosus muscle the muscle is felt at the junction of the penis and the scrotum.
Abnormalities  of  bulbocavernous reflex
Bulbocavernous reflex is absent in
  • Lesion of the local reflex arch of S2-S4
  • Pyramidal lesions
Clinical significance
1.It is a superficial reflex which  has localising value in paraplegia
2.The bulbocavernosus reflex is one of the few ways to test the following
       Conus medullaris (which is the distal end of the spinal cord)
       The S2 to S4 pelvic nerves (the only other bedside test of this region is testing sensation in the             perineal, or “saddle,” area).
3.This reflex is particularly important in patients with urinary retention, that is caused by disease of the pelvic nerves or cauda equina.
This reflex is useful to differentiate between UMN and LMN bladder.
  • UMN bladder—reflex preserved
  • LMN bladder reflex lost
The advantage of bulbocavernosus reflex monitoring is that it will tests the functional integrity of the three different anatomic structures:
In spinal cord injury above the S2 to S4 level (i.e., lesion of upper motor neurons innervating the S2 to S4 segment), the bulbocavernosus reflex also disappears, but only temporarily for a period of 1 to 6 weeks.
Prognostic significance
  • Complete absence of distal motor or sensory function or perirectal sensation, together with recovery of the bulbocavernosus reflex  indicates a complete cord injury, and in such cases it is highly unlikely that significant neurologic function will ever return.
  • Therefore, if no motor or sensory recovery below the level of  lesion is present, patient has a complete spinal cord injury and no further distal recovery of motor function can be expected;
  • On other hand, any spared motor or sensory function below level of injury is considered incomplete spinal cord injury , potential for recovery of incomplete lesion is determined by part of the cord most severely injured
  • Following spinal cord trauma, presence or absence of this reflex carries prognostic significance;
  • In cases of cervical or thoracic cord injury, absence of this reflex documents continuation of spinal shock or spinal injury at the level of  the reflex arc itself;
  • Period of spinal shock usually resolves  within a period of  48 hours and return of bulbocavernosus reflex is a good signals fo termination of spinal shock;
  • Remember that spinal shock does not apply to lesions that occur below the cord, and therefore, low lumbar burst fracturers should not cause spinal shock (and in this situation, the absence of the bulbocaveronsus reflex indicates that there is a cauda equina injury)
  • Persistent loss of the bulbocavernosus reflex may be a result of a conus medullaris injury (eg from an L1 burst fracture )

Root Value of bulbocavernous 
Bulbocavernous reflex is innervated by  S3.S4
The afferent paths of the bulbocavernosus reflex are the sensory fibers of the pudendal nerves
The reflex center in the S2–S4 spinal segment. 
The efferent paths are the motor fibers of the pudendal nerves and anal sphincter muscles