Medical Definition of cogwheel rigidity
: muscular rigidity in which passive movement of the limbs (as during a physical examination) elicits ratchet-like start-and stop movements through the range of motion of a joint (as of the elbow) and that occurs especially in individuals affected with Parkinson's disease The third major sign, rigidity (sometimes called "cogwheel" rigidity), is peculiar to Parkinson's disease. When a limb is bent, it seems to catch at regular points throughout its range of motion, much as a second hand jerks from interval to interval instead of smoothly traversing the face of a clock.—Harriet Washington, The Harvard Medical School Health Letter, May 1993—called also cogwheeling
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