THE PLANTAR REFLEX - RePub

INTRODUCTION
When is an upgoing toe a Babinski sign?
Quivering hallux responses after plantar stimulation are by no means
exceptional. Most physicians react to an uncertain plantar reflex by
stimulating again, or differently, according to their own favourite method
-eponymous or not. The results from Chapter II have taught us, however,
that the process of interpretation is heavily influenced by what the answer
ought to be, rather than by what there is to see. Stimulation is of course
important, but it should not be over-emphasized: re-testing the reflex may
only provide time for bias to become effective, or may even be subordinate
to this purpose. Rare indeed is the physician who goes on stroking the sole
until he has proved that his first ideas were wrong.
A remedy against a 'blind eye' is to reinforce the visual information.
This can be done by the introduction of criteria for the Babinski sign that
are added to a mere upward movement of the great toe. Despite the
prevailing concern with stimulation methods (see Chapter I: 'rival signs'),
some advice has also been offered in the past on what to look for, although
with little rationale:
1. 'The movement should occur at the metatarsophalangeal joint' (Barnes,
1904; Bickerstaff, 1968). This criterion is meant to exclude passive
movement by dorsiflexion of the foot. It is related to action of the
extensor hallucis longus muscle, which proved to be vital in the
preceding chapter. However, it is often less sensitive than inspection of
the tendon of this muscle: the tendon has its insertion at the last
phalanx and can cause movement in the distal joint only, or even tighten
without any displacement at all.
2. 'The movement should be the first' (Barnes, 1904; Bickerstaff, 1968;
Hogan and Milligan, 1971). It is difficult to see why a patient cannot
make a voluntary movement before the onset of reflex action.
3. 'The movement should be slow' (Scholten, 1965; Mumenthaler, 1976).
What is the limit of slowness? Moreover, reports of brisk flexion
reflexes and Babinski signs abound (e.g. Walshe, 1914; Szapiro, 1960).
The flexion reflex
The fact that the Babinski sign forms an integral part of the flexion
reflex in the lower·limb has been discussed in detail in Chapter I. Later it
was specified that the Babinski sign consisted in essence of recruitment of
the extensor hallucis longus into synergy with the tibialis anterior (Landau
87