Chaddock’s sign, or the external malleolar sign, is a variant method for eliciting the plantar response, by application of a stimulus in a circular direction around the external malleolus, or the lateral aspect of the foot, moving from heel to little toe. Extension of the hallux (upgoing plantar response, Babinski’s sign) is pathological, indicating corticospinal tract (upper motor neurone) pathology. The development of Babinski’s sign always predates that of Chaddock’s sign.
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Van Gijn J. The Babinski sign: a centenary. Utrecht: Universiteit Utrecht, 1996