Sciatica is pain and discomfort along the sciatic nerve from irritation or compression. The sciatic nerve travels from your lower back through the buttocks and hips and down the back of each leg. The sciatic nerve is the longest nerve in your body and runs from the back of the pelvis down to the feet. The most common cause of sciatica is from a slipped disc. However, other spinal conditions may also play a major role in causing sciatica. Examples of these spinal conditions include: spinal injury, spinal tumour, or a spinal infection.