A spasm in which contraction and relaxation of a muscle alternate in rapid succession, usually after a sudden passive stretch, and thus sometimes referred to myoclonus. It is observed as a sustained rhythmical tremor of around a joint (e.g., ankle, patella, wrist). Although it can be due to damage to peripheral nerves, most forms of clonus are caused by problems in the central nervous system. However, the precise mechanisms underlying it are not fully understood, and it is possible that the different forms may have different causes. While associated with spasticity, it can be transitorily present in healthy newborns for a few days after birth.
See Cerebral palsy, Newborn, Spasticity