What is “Normal,” Anyway?

This blog is an adaptation of a March 2022 Forum column, for which one can find the full article here.

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.

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 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. 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 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.

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.