THE PLANTAR REFLEX - RePub

Clinical experience appeared to be no safeguard against bias: four of the
twenty subjects had been practising neurology for five years or more and in
them the effect of foreknowledge was similar to that in the others,
although their number was too small for conclusions about relative
probabilities. At the other end of the hierarchy were a few subjects with
only some months' experience, and among these were two of the three
observers whose change of opinion went against the leading information;
it is tempting to speculate that they were 'protected' by a relative
ingenuousness. The third observer who showed a paradoxic variation later
commented that he had actively resisted the influence of the preceding
data.
Prejudice has also marred studies about technique of plantar stimulation.
This is most clearly shown by the originators of rival signs (see Chapter I),
who report almost unanimously disappointing results with Babinski's
method. Bias may also have affected the conclusion of a recent report
(Dohrmann and Nowack, 1973) that slow 'hockey-stick' stimulation
(lateral plantar border and plantar arch) is the 'best' method to produce an
upgoing toe sign: the authors were their own measuring instruments and
did not state what they expected to find.
Need for objective criteria
As interpretation of equivocal plantar reflexes is so much subject to the
combined effect of inconsistency and preconceived ideas, this is not only a
reason for considerable modesty at the bedside, but at the same time it
creates a need for better criteria. The arguments whether or not a doubtful
upward toe movement 'counts' ought to be defined, not intuitive: a
neurologist should not only be able to say that he thinks a particular reflex
is pathological, but also why, in order to make discussion possible.
Previous investigations, cited in the first chapter, stress the intimate
relationship between the Babinski sign and the flexion reflex. It is striking
that the impact of these studies on everyday interpretation of plantar
reflexes has apparently been negligible, as not more than one of the fifty
participants regretted that the films did not show the leg. A fair number
complained that the angle under which the foot was filmed did not enable
them to see a possible 'fan sign' of the toes, but it has been emphasized
earlier (p. 24) that there is little reason to regard this as a sign of disease.
It can be concluded, at least for the large sample of neurologists in this
study, that existing practical rules for interpretation of equivocal plantar
reflexes are insufficient and at best controversiaL In the next two chapters
I will attempt to delineate adequate criteria.
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