The sciatic nerve is the longest and thickest nerve in the body and when irritated can be excruciating
The sciatic nerve is formed by a group of nerves than exit the spine and join together. These nerves can become irritated from disc problems in the spine, or from a tight piriformis muscle.
Whether from an injury or after years of strain, the discs in the spine can weaken and begin to bulge or herniate or they can actually rupture. Bulging and rupturing of the disc can put pressure on the nerve. Chemical changes (think inflammation) also occur causing nerve irritation.
Signs of sciatic nerve irritation:
Pain that travels down the leg. True sciatic pain usually goes below the knee
numbness or tingling in the affected leg
weakness of leg muscles in the leg
pain with sitting more than standing and pain with bending over.