A normal response of the knee muscles that occurs when the physician uses an instrument to strike the leg below the knee joint. This is done as part of a neurological examination to test reflexes.
The extension of the lower leg upon striking the patellar tendon when the knee is flexed at a right angle. Knee jerk is absent in locomotor ataxia, infantile paralysis, meningitis, destructive lesions of the lower part of the spinal cord, and certain forms of paralysis. It is increased in lesions of pyramidal areas, brain tumors, spinal irritability, and cerebrospinal sclerosis.
A sudden forward movement of the lower leg induced by a physician tapping the ligament just below the knee cap while the leg is hanging loosely at a 90-degree angle. This sign is typically present, but its absence can signal a central nervous system disorder. In some cases, it may be challenging to elicit this response from nervous individuals, as they tend to keep their leg rigid and resist allowing it to kick out.