Cauda Equina Syndrome
Compression of the lumbosacral nerve roots below the spinal cord causes bilateral sciatica, saddle anaesthesia and bladder or bowel dysfunction together, because they share one anatomical compartment, and this is a time-critical surgical emergency.
First principles
The cauda equina is a bundle of nerve roots, not the cord itself: hence the pattern of injury
The spinal cord ends at approximately L1/L2, below which the spinal canal contains a loose bundle of lumbar and sacral nerve roots (the cauda equina) floating in cerebrospinal fluid before exiting at their respective foraminae. Because these are peripheral nerve roots rather than cord, compression here produces a lower motor neurone pattern (flaccid weakness, reduced or absent reflexes and root-pattern sensory loss across multiple levels) rather than the upper motor neurone picture seen with cord compression above L1.
Educational content pending clinical review. Not medical advice.