The reflex occurs upon stroking of the sole of the foot with a blunt object such as a pen. If the reflex occurs in adults as illustrated at bottom it may be due to nerve damage or disease.
The plantar reflex is a
reflex elicited when the sole of the foot is stimulated with a blunt instrument. The reflex can take one of two forms. In healthy adults, the plantar reflex causes a downward response of the
hallux (
flexion). An upward response (
extension) of the hallux is known as the Babinski response or Babinski sign, named after the neurologist
Joseph Babinski. The presence of the Babinski sign can identify
disease of the
spinal cord and
brain in adults, and also exists as a
primitive reflex in
infants.[1]
The
lateral side of the
sole of the foot is rubbed with a blunt instrument or device so as not to cause pain, discomfort, or injury to the skin; the instrument is run from the heel along a curve to the
toes[4] (
metatarsal pads). Many
reflex hammers taper at the end of the handle to a point which was used for testing the plantar response in the past; due to the tightening of
infection control regulation this is no longer recommended. Either a single use device or the thumb nail should be used.[citation needed]
There are three responses possible:
Flexor: the toes curve down and inwards, and the foot
inverts; this is the response seen in healthy adults.
Indifferent: there is no response. This is called the neutral response, and has no clinical significance, as it does not rule out pathology.[5]
Extensor: the
halluxdorsiflexes, and the other toes fan out. If elicited in an adult, it indicates damage to the
central nervous system, but it is a normal reflex in infants (see below). It is also known as the Babinski Sign.
As the
lesion responsible for the sign expands, so does the area from which the
afferent Babinski response may be elicited. The Babinski response is also normal while asleep and after a long period of walking.
Interpretation
The Babinski sign can indicate
upper motor neuron lesion constituting damage to the
corticospinal tract. Occasionally, a pathological plantar reflex is the first and only indication of a serious disease process and a clearly abnormal plantar reflex often prompts detailed
neurological investigations, including
CT scanning of the brain or
MRI of the spine, as well as
lumbar puncture for the study of
cerebrospinal fluid.
The phrase "negative Babinski sign" is sometimes used for the normal flexor plantar response.[6]
Infants will usually show an extensor response. In one study of 256 healthy infants, the response to testing was extensor in 73.8%, flexor in 8.9%, and equivocal in 17.3%[7] This extensor response occurs because the
corticospinal pathways that run from the
brain down the
spinal cord are not fully
myelinated at this age, so the reflex is not inhibited by the
cerebral cortex. The extensor response usually disappears – giving way to the flexor response – by 12 months of age.[8] Its persistence beyond age 2–3 indicates a problem in the brain or spinal cord.[9][10]
Pathways
Afferent:
Nociception detected in the S1 dermatome and travels up the tibial nerve to the sciatic nerve to roots of L5,S1 and synapse in the anterior horn to elicit the motor response.
Efferent: Motor response back through the L5,S1 roots to the sciatic nerve to its bifurcation. Toe flexors are innervated by the tibial nerve. Toe extensors (extensor hallucis longus, extensor digitorum longus) are innervated by the deep peroneal nerve. Loss of normal adult descending pyramidal control of the reflex arc to suppress extensor withdrawal results in the upgoing toes in the plantar reflex known as Babinski's sign.[11]
The
Hoffmann's reflex is sometimes described as the
upper limb equivalent of the Babinski sign[12] because both indicate
upper motor neuron dysfunction. Mechanistically, they differ significantly; the finger flexor reflex is a simple
monosynaptic spinal reflex involving the
flexor digitorum profundus that is normally fully inhibited by upper motor neurons. The pathway producing the plantar response is more complicated, and is not monosynaptic.
Babinski-like responses
The plantar reflex can be elicited in a number of ways, which were described in the late 19th and early 20th century. These have their own eponyms.[13][14][15]
^Acharya, Aninda B.; Jamil, Radia T.; Dewey, Jeffrey J. (2023),
"Babinski Reflex", StatPearls, Treasure Island (FL): StatPearls Publishing,
PMID30085551, retrieved 2023-12-04, If there is no movement, then this is considered a neutral response and has no clinical significance." "Sometimes there is no response to stimulation. This is called a neutral response. This response does not rule out pathology.
^Futagi, Y; Suzuki, Y (August 2010). "Neural mechanism and clinical significance of the plantar grasp reflex in infants". Pediatric Neurology. 43 (2): 81–6.
doi:
10.1016/j.pediatrneurol.2010.04.002.
PMID20610116.
^Harrop JS, Hanna A, Silva MT, Sharan A (2007). "Neurological manifestations of cervical spondylosis: an overview of signs, symptoms, and pathophysiology". Neurosurgery. 60 (1 Supp1 1): S14–20.
doi:
10.1227/01.NEU.0000215380.71097.EC.
PMID17204875.
S2CID22166615.
^Walker, H. Kenneth; Hall, W. Dallas; Schlossberg, J. Willis Hurst; illustrations by Leon; Boyter, Charles H. (1990).
"Chapter 73 The Plantar Reflex". In Walker, H. Kenneth (ed.). Clinical methods : the history, physical, and laboratory examinations (3rd ed.). Boston: Butterworths.
ISBN978-0-409-90077-4. Table 73.1 Variants of the Babinski Sign