Many clinicians will habitually group feet they see in clinic; some based on cursory observation (“they are a pronator/overpronator” etc) and some may do so more formally after performing something such as the Foot Posture Index (FPI-6). Whilst it may be descriptively accurate to call a foot a +3 or a +12 (and then attach the associated pre-designated labels) if the FPI-6 is your weapon of choice, what context this is then put in (given the inter-rater reliability of the FPI-6 in your own hands/department, how/if this correlates with dynamic function and ultimately how this information will be used to actually manage the patients) is key here. The expectation of a large number of feet with an identical ‘label’ should certainly not be that they will behave identically in terms of their kinematics and kinetics, and this for me is the crux of why I personally do not categorise or label feet in the clinical setting.
Whereas most would certainly be able to differentiate between say a +12 and a -12 as defined by the FPI-6 (the feet at each extreme of the spectrum), could the same differentiation be said of the majority of feet in the middle? Furthermore, the use of arbitrary lines in the sand to suggest normality and abnormality is hugely flawed. A wonderful analogy of this was given by American Orthopaedic Surgeon Mr Henry Feiss back in 1909:
“Given a series of objects animate or inanimate, which differ from one another only to a slight extent, it is impossible to state just where we should draw the line dividing one group from another. If we take one hundred shades of color, say yellow, and arrange these shades in a graded series from a light yellow to a brown, the differences between the individual shades which are placed next to each other are so slight as not to be detectable. Yet if we compare the beginning with the end of the series, the difference is very striking. The same holds good in a given structure in the human body in which the individuals are arranged in a series according to the variations in that particular structure…. This, then, is our problem; the difficulty in dividing the series is apparent; there is no natural dividing line in this arrangement which can be used to define the limits of normality.”
Yes, that was published in 1909. That isn’t a typo. This paper is one of my favourite papers of all time. It was sent to me by my friend and mentor Simon Spooner several years ago and I re-read it regularly. Its got some other brilliant paragraphs in it that everyone should see. This is a link to my dropbox where the full PDF can be accessed. I’d encourage everyone who reads it to constantly remind themselves as they are doing so that is was written 108 years ago. Simply brilliant. Enjoy.
