Where Does it Hurt?

In the illustrations here, the letters L1-L5 refer to the lumbar (lower) portion of the spine.  Letters S1-S2 refer to the first two sacral vertebrae.  Over 90% of herniated disc injuries occur at the L4-L5 and L5-S1 discs.

In this box, a cross section of the lumbar and sacral vertebrae shows spinal nerve roots branching off the spinal cord.  Each nerve root is depicted in a different color, corresponding to regions of the pelvis and legs (far right) that can be afflicted by pain, tingling, or numbness when the spinal nerve roots are compressed.

What is Sciatica?

Sciatica is the sensation of pain, tingling, or numbness in the buttocks and/or legs produced by an irritation of the sciatic nerve.  Multiple nerve roots extend from each side of the spinal cord in the sacral area (right above your tailbone), and join to form the sciatic nerve.  The sciatic nerve actually only exists for a short length down the buttock, after which it branches into various nerves.  These smaller nerve branches then travel down the leg, reaching the ankle and foot.  The primary causes of sciatica are herniated, bulging, or degenerated discs, which put pressure on the spinal nerve roots.  Other causes include bony growths on the spine (bone spurs) or compression of the nerves through injury.  In rare cases, the sciatic nerve may be irritated by conditions such as tumors, pregnancy, or piriformis syndrome.