Sciatica occurs when something happens to the sciatic nerve. This nerve is found in the back of your leg. It controls muscles in the back of your knee. It gives you sensation in your lower leg, thigh, and sole of your foot. Sciatica refers to bad pain, weakness, or tingling in your leg. Sciatica is caused by injury. Sciatica is not a medical condition by itself, but a symptom of another medical issue.