The bulbocavernosus reflex is a contraction of the anal sphincter and bulbospongiosus muscle when the glans penis or clitoris is squeezed, or when a urinary catheter is gently tugged. It tests the S2-S4 segments through the pudendal nerve. It is a key reflex in assessing spinal cord injury.
| Nerve root | S2-S4 |
|---|---|
| Area | Glans penis or clitoris (squeezed), with the response felt at the anal sphincter |
| How to test | With a gloved finger in the anal canal, the examiner squeezes the glans penis or clitoris, or gently pulls on an indwelling catheter, and feels for anal sphincter contraction. |
| Muscles | |
| Nerve Supply | Pudendal nerve |
Tests the integrity of the sacral reflex arc that underlies bladder, bowel and sexual reflexes.
The return of the bulbocavernosus reflex is often used as a marker that spinal shock is ending, typically within the first days after injury; if there is still no function below the injury at that point, the injury is likely complete. Its absence in a conscious patient with back pain suggests a conus or cauda equina lesion.
Temporary loss of reflexes below an acute spinal cord injury; this reflex is usually among the first to return.
Compression of the sacral roots abolishes this reflex along with sphincter control and saddle sensation.
A lesion of the lowest spinal cord segments abolishes the reflex and causes early bladder and bowel dysfunction.
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