Response, plantar

The plantar response, also known as the Babinski response, is an important neurologic examination based upon what the toes do when the sole (the plantar surface) of the foot is stroked. If the big toe goes up, that may mean trouble.

The plantar response is obtained by stimulating the external portion (the outside) of the sole. The examiner begins the stimulation back at the heel and goes forward to the base of the toes. There are diverse ways to elicit the plantar response . A useful way that requires no special equipment is with firm pressure from the examiner’s thumb. Just stroke the sole firmly with the thumb from back to front along the outside edge.

Too vigorous stimulation may cause withdrawal of the foot or toe, which can be mistaken as a plantar response .

Most newborn babies give a plantar response nervous system is far from their nervous system is not mature. Upon stimulation of the sole, they extend the great toe. Many young infants do this, too, and it is perfectly normal. However, in time during infancy the plantar response vanishes and, under normal circumstances, should never return.

A plantar response in an older child or adult is abnormal. It is a sign of a problem in the central nervous system (CNS), most likely in a part of the CNS called the pyramidal tract.

Asymmetry of the plantar response — when it is present on one side but not the other — is abnormal. It is a sign not merely of trouble but helps to lateralize that trouble (tell which side of the CNS is involved).

The plantar response is known by a number of other names including the toe or big toe sign or phenomenon and the Babinski reflex, phenomenon or sign (from the late French neurologist who described it).

It is, incidentally, quite common but entirely wrong to say that the plantar response is positive or negative; it is present or absent.

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