Both caregiver222 and jemma116 have provided accurate information.
The two sciatic nerves are the largest nerves in the human body. They are formed on each side from elements of the lumbar nerve roots, and runs beneath the piriformis region in the pelvis, exiting the pelvis at the greater sciatic foramen, where it runs down the back of the thigh to an area just above the knee. Here it divides into the tibial and fibular nerves.
This is why sciatic pain is often felt in many areas -- the lower back, the buttocks and groin, the back of the leg, and the knee.
However, the condition known as sciatica is generally caused by inflammation at the origin of this nerve -- along the lumbar spine. This ice and other anti-inflammatory remedies usually work best when applied along side of the lumbar spine where pain is felt, above the erector s. and quadratus l. muscles, above the hip bone.
Some people receive relief at pressure points located in the center of the buttock, the mid-thigh, and back of the knee.
Lately I've seen a television commercial for an elastic band with "magical" properties, designed to apply pressure to these pressure points to relieve sciatic pain.
Be wary of any remedy that makes claims that promise to relieve the pain of a complex medical problem with a simple device. In my long experience with chronic pain, I've seen bands for headaches, back aches, and now sciatica.
These rarely have any effect on your pain, other than to lighten your wallet.
Incidentally men (and women, a thick wallet carried in the back pocket can aggravate sciatica. So can a pair of shoes that offer minimal support if you have a job that requires a lot of standing or walking.
Posture that balances your vertical and horizontal alignment against gravity helps minimize the pain of spine disease. This is why sleeping in a sagging bed, slouching in a chair, or leaning can exacerbate back pain. People with "bad backs" or necks who wish to avoid osteoarthritis should always be aware of their body's location in space, and adjust their posture to place minimal strain on the cord, nerve roots, discs, facets, and uncovertebral joints.
The proper position is over the lumbar vertabrae L1-L-5. Sleep with a pillow between your legs. You will really benefit from some professional rehab therapy from a specialist who will teach you several exercises. You can't lean them on you-tube. This will be the best money you every spent.
The sciatic nerve is the area of the lower back. The nerve is impinged and the pain is radiating down the back of your leg.
Place your heat pack or your cold pack, whichever gives you benefit, in the lower back.