clasp knife phenomenon

A manifestation of corticospinal spasticity in which there is increased tone in either flexion or extension with sudden relaxation, as the muscle continues to be stretched, imparting a sensation likened to that of an opening clasp knife, which has initial resistance and then opens more easily
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clasp knife phenomenon

Neurology A manifestation of corticospinal spasticity, in which there is ↑ tone in either flexion or extension with sudden relaxation, as the muscle continues to be stretched, imparting a sensation likened to that of an opening clasp knife; the CKP is often accompanied by weakness of the affected extremity, ↑ tendon reflexes, and a Babinski sign. Cf Cogwheel phenomenon, Gegenhalten.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.