Meningitis, Kernig sign of

This clinical hallmark of meningitis, inflammation of the meninges, the membranes covering the brain and spinal cord, is tested for by having the person lie supine (flat on the back), flex the thigh so that it is at a right angle to the trunk, and completely extend the leg at the knee joint. If the leg cannot be completely extended due to pain, this is Kernig sign.