Sciatica refers to pain, weakness, numbness, or tingling in the leg. It is caused by injury to or pressure on the sciatic nerve. The sciatic nerve starts in the lower spine and runs down the back of each leg. This nerve controls the muscles of the back of the knee and lower leg and provides sensation to the back of the thigh, part of the lower leg, and the sole of the foot. In some cases, the pain is severe enough to make a person unable to move.
Sciatica, Mayo Clinic (Aug. 14, 2015), https://www.mayoclinic.org/diseases-conditions/sciatica/symptoms-causes/syc-20377435