What is a “Normal” Foot?

Over a half-century ago, Dr. Merton Root and his colleagues made the bold proposal that a set of eight “biophysical criteria” were necessary for an individual to have a “normal” foot and lower extremity. Root and team published that a “normal” foot and lower extremity must possess the following characteristics:¹

• the distal one-third of the leg should be vertical;

• the knee, ankle, and subtalar joint (STJ) should lie in the transverse plane parallel to the supporting surface;

• the STJ should rest in its neutral position;

• the bisection of the posterior calcaneus should be vertical;

• the midtarsal joint should be “locked” in its maximally pronated position;

• the plantar plane of the forefoot and rearfoot should both be parallel to the supporting surface;

• metatarsals 2, 3, and 4 should be totally dorsiflexed with the metatarsal heads in a common plane parallel to the supporting surface; and

• the heads of metatarsals 1 and 5 should be in the same transverse plane position as metatarsal heads 2, 3, and 4.¹

In this age of evidence-based medicine, one should regard scientific research as based on a higher level of evidence than that of expert opinion.² Accordingly, then, one might ask what research Dr. Root and colleagues utilized to support their claims that these 8 “biophysical criteria for normalcy” were, indeed, necessary to have a normal or ideal foot. Unfortunately, there was no such research detailed in the book where Root and colleagues first published their “biophysical criteria for normalcy.”¹ Perhaps the most significant error that Dr. Root and colleagues made when proposing these criteria is that they used 8 hypothetical structural and/or joint position parameters to describe all the ways that an individual’s foot and lower extremity could become “not normal” or “abnormal.” Rather, I believe that these authors should have instead used the term “hypothetical ideal values” to describe what they believed were optimum structural and joint position values for the foot and lower extremity.

As far as I am aware, no other branch of medicine uses the term “normal” to describe a set of very specific and ideal structural and joint position values for an extremity. Instead, the term “normal” within the medical research community describes a range of values within a measurable biological parameter present in many healthy individuals.

When is “Normal” a Range?

When we order any blood or serum test for our patients, previous scientific research will inform us of the range of normal or “reference” values found in large groups of healthy and asymptomatic individuals. The scientific literature doesn’t give one discrete “normal” value that they claim is “ideal” for any specific blood or serum measurement parameter. For example, when one of our adult male patients has a hematocrit of 41 percent, we don’t say that the hematocrit is “abnormal” and that their hematocrit must be 43 percent, or some other specific mid-reference range value. Rather, such laboratory tests have a range of normal or reference values instead of one specific value representing the only “normal” value.

The rest of the medical world seems to realize that there is a wealth of diversity within the human population and that there are a relatively large range of measurable biological parameters that can exist within individuals that still result in healthy function. In my experience, individuals don’t need to have a specific calcaneal heel bisection position, a neutral subtalar joint, or a “locked midtarsal joint” to have healthy lives any more than they need to have one specific hematocrit value in order to be healthy.

In Summary

Since we, as podiatrists, want to be considered the foot and lower extremity experts within our medical communities, we need to embrace the diversity of the individuals we treat and realize that a relatively large range of structural variation can constitute a range of “normalcy.” In other words, we should stop continuing to believe that there are a discrete set of structural and joint position variables required for an individual to possess a “normal” foot and lower extremity. I strongly believe that the intellectual integrity and growth of the podiatric profession depends upon it. 

Dr. Kirby is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is in private practice in Sacramento, Calif.

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References

1. Root ML, Orien WP, Weed JH, Hughes RJ. Biomechanical Examination of the Foot, Volume 1. Clinical Biomechanics Corporation;1971:34.

2. Sackett DL. Rules of evidence and clinical recommendations on the use of antithrombotic agents. Chest. 1989;95:2S–4S.