The displacement can be within the disc (a) or bulge without penetration of the annulus fibrosis (b) or it can herniate through the annulus fibrosis into the spinal canal (c)
Most cases of cauda equina result from disc protrusion
The intervertebral discs are a secondary cartilaginous joint
They have a tough outer layer (the annulus fibrosis) and a gelatinous core (nucleus pulposus)
Cartilaginous end plate of each disc attaches to bony endplate of vertebra
In a disc prolapse, the nucleus pulposus is displaced from the intervertebral space