THE PLANTAR REFLEX - RePub

to happen because impulses are unable to reach the short toe flexors. On
the other hand, active muscular tension in the patient is of course
restricted to intact muscles: even a few discharging extensor hallucis
longus motor units might then cause upward quivering of the great toe.
This could have been the case in patients 6 and 7, who suffered from
polyneuropathy. The flexor hallucis brevis, being more distal, was probably
most involved, and in fact both patients showed scattered extensor hallucis
longus activity, versus even fewer and later potentials of flexor hallucis
brevis in one patient and none at all in the other. This possible mechanism
does not detract from the principle that one need not be aware of the
peripheral lesion to disqualify these upward toe movements if they are
unrelated to the flexion reflex.
8. Pes cavus. This deformity has also acquired some notoriety for producing
false-positive Babinski signs (Mumenthaler, 1976). It is true that the
primary upward position ol the great toe mechanically favours further
dorsiflexion by even the slightest activity of the extensor hallucis longus.
This is the more so because pes cavus is often accompanied or even caused
by atrophy of intrinsic foot muscles (Thomas, 1975; the hypothesis of
Collier (1899) that increased tone of the extensor hallucis longus contributed
to the deformity is untenable). But again, when the upward
movement of the great toe is a genuine reflex (patient 10), it signifies
abnormal processing of impulses in the spinal cord, irrespective of
peripheral anatomy.
Lacking Babinski response
Finding an equivocal plantar response in the presence of other pyramidal
signs is almost the reverse situation of finding it as an isolated phenomenon,
and usually it presents fewer problems of clinical management. Close
attention to toe movements in their relation to action of other leg muscles
may also be helpful in this group, as shown above by the comparison of
electromyographic results with clinical data. If a Babinski response is truly
absent there are three possible reasons:
1. ]oint deformity. This is not unusual, especially in the form of hallux
valgus. Figure 11 illustrates occult Babinski signs in a patient who could
not even move his great toes voluntarily because of hallux valgus.
2. Peripheral nerve lesions. Pressure palsy of the lateral popliteal nerve is
(or at least was) a common complication of chronic paraplegia, and
precludes a Babinski sign (Collier, 1899; Marie, 1912; Marie and Thiers,
1913; Guttmann, 1952; Grossiord and Kahn, 1957; Landau and Clare,
1959). The same problem can occur at another level in motor neurone
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