THE PLANTAR REFLEX - RePub

little or no value as a feature of pyramidal involvement. The recent claim
of Hindfelt et al. (1976) that the 'crossed upgoing toe sign' can be regarded
as a reliable and sometimes superior test is not confirmed by my study, nor
by previous work.
In contrast, the occurrence of mirror movements when fast toe movements
were attempted in a weak foot proved to be a much less equivocal
sign, although it did not provide new information.
ACTIVITY OF THE FLEXION REFLEX
A prerequisite for the Babinski sign
As the Babinski sign is part of the flexion reflex synergy (see Chapter I),
the flexion reflex pathways have to be activated in order to produce an
upgoing toe. Recruitment of the extensor hallucis longus is only rarely the
minimal response: in the SO patients with a unilateral Babinski sign the
stimulus intensity was no higher than necessary to elicit a clear hallux
response, and in 48 of the SO patients more proximal leg muscles were
activated at the same time (figure 12). Although no special notes were kept
about relative thresholds, and individual variations could occur, the tensor
fasciae latae was often the first muscle to respond visibly (Brissaud, who
described this part of the flexion reflex in 1896, found the same). On more
intense stimulation this response is joined successively by tibialis anterior
(with or without extensor hallucis longus), by knee flexors at comparable
thresholds, and finally by hip flexors when the reflex is very active. Landau
and Clare ( 19S9) recorded electromyographically from several leg flexors
and found activity of the tensor fasciae latae only late in the sequence, i.e.
with strong stimuli, but on inspection contraction of this muscle is easy to
note because of its superficial location. In patients with paraplegia, Walshe
(1914) found the biceps femoris muscle to be the motor focus of the
flexion reflex, whereas Dimitrijevic and Nathan (1968) observed individual
idiosyncratic responses.
With these qualifications in mind, we may assume that the motoneurones
of the extensor hallucis longus muscle are usually not the first to be
activated by the flexion reflex pathways in patients with a Babinski
response. Hence when a Babinski sign is absent in a weak foot, we may
infer from an absent or feeble response in proximal leg flexors that there
is insufficient activity in the flexion reflex pathways that project upon the
extensor hallucis longus muscle. This inexcitability may be the result of
individual variation (case 12, p. 133) or of initial reflex depression (case 13,
p. 133 ). Conversely, a Babinski sign can disappear because the activity of the
flexion reflex dwindles after the acute episode (case 11, p. 132).
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