THE PLANTAR REFLEX - RePub

Recording the plantar reflex
INTRODUCTION
An important step towards defining the pathological plantar response
clinically is to make use of permanent records in some form, rather than
relying on inspection of fleeting movements. Such a method might be used
first in reference groups of unequivocally upward and downward toe
responses, and might subsequently be applied to dubious cases.
Before the advent of techniques that could measure muscular activity
itself, mechanical registration of displacement was the only method of
obtaining a graphic representation of motor phenomena. Verger and
Abadie (1902, 1904) were the first to apply this to reflex movements of the
great toe. Theit tracings showed that the Babinski sign as well as the
normal response occurred simultaneously with contraction of tibialis
anterior and tensor fasciae latae. Walshe (1914) confirmed the temporal
relationship between the Babinski response and the flexion reflex, but
Meyers (1920) found the Babinski sign to be synchronous with activity in
'other' extensor muscles, i.e. quadriceps and gluteus. Apart from being an
indirect technique, mechanical recording has other pitfalls such as superposition
of movements and delay of transmission: latencies for the
Babinski sign varied from 0.1-0.14 seconds (Verger and Abadie, 1902) to
0.2-0.52 seconds (Herzog, 1918).
Electromyography and the Babinski sign: the extensor hallucis longus
When recording of electrical activity from muscles became feasible, it
was necessary to choose a specific muscle as the effector of the Babinski
sign: either the extensor hallucis longus in the lower leg or the extensor
hallucis brevis on the dorsum of the foot. The choice was not particularly
difficult, as in fact no one had ever considered anything else than the
extensor hallucis longus (table VII).
The string galvanometer which had made electrocardiography possible
was used by Wertheim Salomonson (1918, 1920) to record from the
extensor hallucis longus muscle in patients with a Babinski sign. However,
he found that only the beginning of the upgoing toe sign was accompanied
by alternating currents, and most of the movement took place under
electrical silence. A similar sequence of events was found for voluntary
activity. Wertheim Salomonson concluded that the initial response ('tetanus')
represented the Babinski reflex proper, while the ensuing movement
('tonus contraction') was secondary to it and might even take place in a
separate part of the muscle. Today we know that these theoretical
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