The sciatic nerve is the primary nerve that runs down the back of the leg. It branches from the lower spine and runs the entire length of the leg and foot.
Because of its length and direct connection to the spine, the sciatic nerve is vulnerable to pain from multiple causes. Lumbar spine injury are a cause of pain in the sciatic nerve; when the discs swell due to injury, they compress the nerve. Muscle injury in the leg and hip is also a cause of sciatic nerve pain. Sciatic nerve injury sometimes spreads to the entire leg, causing numbness, pain and weakness.