Sciatica is pain resulting from irritation of the sciatic nerve. Sciatica pain is typically felt from the low back to behind the thigh and radiating down below the knee. The sciatic nerve is the largest nerve in the body and begins from nerve roots in the lumbar spinal cord in the low back and extends through the buttock area to send nerve endings down the lower limb.
However, some people only experience pain or numbness in the calf of the leg, or in the foot, while the source of the problem is actually located in the low back. This is because sciatica is most commonly a result of a lumbar (low back) disc herniation directly pressing on the sciatic nerve. Moreover, any cause of irritation or inflammation of this nerve as it comes out of the spine in the low back can reproduce the symptoms of sciatica.