What is a knee nerve block? Nerve block it is a medical procedure that involves injecting a local anesthetic medication into specific nerves around the knee to block pain signals from reaching the brain. This procedure is often used to relieve pain and discomfort before and after knee surgery, or as a treatment for chronic knee pain conditions such as arthritis. Using ultrasound or other imaging techniques, the doctor identifies the nerves to be targeted and inserts a thin needle into the area.