Plantar Reflex - medIND

leg should be positioned in such a way that the knee is
straight or slightly flexed and the thigh externally rotated.
It is important to distract the patient with conversation after
warning him that the sole of the foot will be scratched. It is
advisable to hold the patient’s ankle with one hand, to keep
the foot in place and control the pressure of the plantar
stroke. The stimulus should be firm, gentle and should cause
neither pain nor tickle. A sharp stimulus is applied only if
the initial stimulus fails to elicit a response. The response
can be reinforced by rotation of the patient’s head to the
opposite side. Following the stimulus, it is important to
watch the big toe at the metatarsophalangeal joint and the
remainder of the foot. The response usually occurs after
the plantar stroke has moved a few centimeters along the
sole to produce a spatial and temporal summation of the
applied stimulus.
Interpretation of the response
The plantar response may be:
1. Normal flexor plantar response
2. Pathologic or abnormal extensor plantar response
(Babinski’s sign)
Normal flexor plantar response
In normal people after infancy, there is a plantar flexion of
the foot and toes along with adduction of the toes. The
primary movement is a plantar flexion of the great toe at
the metatarsophalangeal joint, even if the terminal joint
appears to extend. The response is a fairly rapid one and
may be accompanied at times by an associated flexion of
the hip and knee on the stimulated side.
Abnormal extensor plantar response
(Babinski’s sign)
Joseph Babinski, a French neurologist, first differentiated
between a normal and a pathologic plantar response and
described the Babinski sign in 1896. The Babinski’s sign is
encountered in patients with pyramidal tract dysfunction
and is characterised by a dorsiflexion or extension of the
great toe with or without fanning or abduction of the
other toes. The fully developed response is also
accompanied by dorsiflexion of the ankle and flexion of
the hip and knee joint and slight abduction of the thigh,
leading to a withdrawal of the leg on plantar stimulation.
The Babinski sign is always pathological. There is no such
thing as a negative Babinski sign.
The muscles taking part in a fully developed response
include the extensor hallucis longus, tibialis anterior,
extensor digitorum longus, hamstring group of muscles,
and the tensor fasciae latae. The dorsiflexion of the toes
may be the only visible effect, but the contraction of the
thigh and leg muscles is always present and can be
detected by palpation. Contraction of the tensor fasciae
latae has been referred to as Brissaud’s reflex.
The fully developed extensor plantar response forms part
of the primitive ‘flexion reflex synergy’ of the lower limbs
designed to withdraw the limb from a painful stimulus.
This spinal defence reflex mechanism described by
Sherrington, activates all the muscles involved in
shortening the stimulated limb. It involves flexion of the
hip and knee, dorsiflexion of the ankle and extension of
the great toe. The ‘toe and foot extensors’ although named
extensors by anatomists, are in fact flexor in a physiological
sense, because their action is to shorten the limb and
contract reflexly alongwith other flexor muscles. The
physiologist looks on the Babinski sign as simply a part of
the ‘primitive flexion reflex’.
The Babinski sign may be a normal occurrence in the first
year of life. In the infant, before myelination of the nervous
system is complete and an upright stance has been
achieved, the normal plantar response is extensor, due to a
brisker ‘flexion synergy’ as part of the withdrawal response
to pain. As the nervous system matures and the pyramidal
tracts gain more control over spinal motor neurons, the
‘flexion synergy’ becomes less brisk and the toe ‘extensors’
are no longer a part of it. When the child assumes an upright
posture, the plantar response becomes part of the postural
reflex maintaining the tones of the foot and leg. At this time,
the normal response to stimulation becomes a flexor
movement of the toes and the ‘withdrawal extensor’
movement is suppressed by the influence of the pyramidal
tract over the spinal reflex arc. The toe then goes down
instead of up, as a result of a segmental reflex involving
small foot muscles and the overlying skin.
The pyramidal tract thus maintains a suppressor action
on the ‘flexion reflex’ synergy. Pyramidal tract dysfunction
however, allows the response to revert to the primitive
194 Journal, Indian Academy of Clinical Medicine Vol. 6, No. 3 July-September, 2005