Tissue Stress Theory: Just A Variation On Root Theory?

The following is a rebuttal to your cover feature, “Has Tissue Stress Theory Supplanted Root Theory?,” by Kevin Kirby, DPM, in the April 2015 issue.

The Root paradigm has existed for over 35 years and has brought order to the field of lower extremity biomechanics. Dr. Kirby’s methods will not build a better functional orthotic device but just another fancy arch support.

Dr. Kirby has the tail wagging the dog. His theories are subservient to the Root paradigm. In other words, they are built on the bones (pun intended) of Root theory. Soft tissues are not the usual cause of foot deformity but the result of being traumatized by forces greater than soft tissue can or was intended to resist.  

Let us look at some of his recommendations for his orthotic design. In regard to the medial heel skive, how do you quantify how much to skive or is it one skive fits all? Now let us add the cushioning material to the heel, which will delay transmission of forces from the ground to the shoe to the orthosis and finally to the foot. Start with a supinated subtalar joint, add a deep heel cup filled with soft cushioning material and you have a formula for propulsive instability. In order for the foot to convert from a mobile adapter to a rigid lever, prior to heel lift, the midtarsal joint must be fully pronated about both its axes. Any delay in this requirement for propulsive stability will result in trauma and damage to soft tissues.

Looking to treat plantar fasciitis by cushioning the heel is a waste of time since the pathology that creates the deformity and disability occurs in the propulsive period of gait when the foot has left the shell of the orthoses and has to stand on its own. Failure to have a fully pronated midtarsal joint will result in collapse of the arch and create the tension to the plantar fascia that produces a periostitis at the proximal attachment of the ligament. Repeated episodes of propulsive instability will tear the periosteum from the heel and produce a heel spur.

This is just one of the many problems with the Kirby tissue stress theory.  

When we first published volume 2 of our series on biomechanics, we knew and hoped it would not become a be-all and end-all of our profession’s knowledge of lower extremity biomechanics.¹ But instead of making positive amendments to basic Root biomechanics, attempting to tear it down and replace it with an invalid and incomplete Kirby paradigm neither serves our profession nor adds to our knowledge of biomechanics. It appears the author’s aim is to replace Root theory with Kirby theory. He states in his article, “In my opinion, tissue stress theory will eventually supplant the evaluation and treatment techniques advocated by Root and colleagues within the next decade.”  

Dr. Kirby is certainly entitled to his opinion but the profession will determine what stays and what goes. It is my opinion that without Root theory as the underpinning of his “theories,” our profession will see if there is any merit to his theories. If they are valid, they can only exist as an addendum to Root theory.

Dr. Kirby should take a lesson from the great music composers of the past centuries. When they wrote a new piece that was based on another composer’s work, they called it what it truly was. Anton Arensky wrote “Variations on a theme by Tchaikovsky, Op. 35a,” Johannes Brahms wrote “Variations on a theme of Paganini, Op. 35,” etc. These great men gave credit where it was due. They did not try to take credit for their work as an entirely new composition.

Kevin, stop trying to replace Root. Be honest and call what you are doing with your current flawed theory what it really represents: “Variations on a theme by Root, Orien and Weed.”¹

— W.P. (Bill) Orien, DPM
Private practice, Santa Barbara, Calif.

Reference

1. Root ML, Orien WP, Weed H. Normal and Abnormal Function of the Foot, Volume II. Clinical Biomechanics Corporation, Los Angeles, 1979.

In Defense Of Tissue Stress Theory

Thank you to Dr. Orien for his letter regarding my cover feature “Has Tissue Stress Theory Supplanted Root Theory?” Having been a student of Drs. Root, Weed and Orien, I am honored to have Dr. Orien critique my thoughts on the current state of foot biomechanics and foot orthosis theory within the international podiatric profession. However, I need to make a few points to better clarify my views on these important subjects for the international podiatric profession.

First of all, I did not invent tissue stress theory. Rather, Tom McPoil, PT, PhD, and Gary Hunt, PT, DPT, OCS, CPed, first coined the term “Tissue Stress Theory” in their article on the foot orthosis treatment of foot and lower extremity conditions, which was published 20 years ago.¹ In their article, McPoil and Hunt discussed the many problems and inaccuracies associated with the theories proposed by Root and colleagues including interrater errors associated with their proposed measurement techniques and problems associated with their notion that there is a single “normal” foot alignment.^2,3

This excellent review paper from two decades ago by McPoil and Hunt described the many serious issues with the theories proposed by Root and colleagues, and should be required reading for all podiatrists. Therefore, I suggest that if Dr. Orien needs to assign an individual’s name to tissue stress theory, he should choose to use the names of McPoil and Hunt in front of tissue stress theory rather than my own.

Secondly, academics have now taught the concept of tissue stress theory on a national and international level at podiatric conferences, and within podiatric academic discussion groups for over a decade. In fact, the largest annual podiatric biomechanics seminar in the United Kingdom, Biomechanics Summer School 2015, was just held on June 19-20 in Manchester. The seminar was titled “The Tissue Stress Theory and Its Clinical Relevance.” The opening keynote lecture was titled “Tissue Stress Theory: Changing the Paradigm in Biomechanical Therapy for the Foot and Lower Extremity.” I was invited to give lectures and workshops at the seminar along with my colleagues Chris Nester, PhD, Geza Kogler, PhD, CO, BCO, LO, LPed, Ian Horsley, PhD, Australian podiatrist Simon Bartold and United Kingdom podiatrist Ian Griffiths on tissue stress concepts at this excellent annual podiatric biomechanics conference.

During this sold-out conference, which was attended by podiatrists, osteopaths, physiotherapists and pedorthists from five countries, panelists discussed the latest research on the effects of foot orthosis geometry on foot tissue biomechanics, tissue stress biomechanical theory, sports injury tissue mechanics, and midtarsal joint biomechanics in detail. It was, however, interesting to note that, during the two days of lectures and workshops at this cutting-edge international podiatric biomechanics conference, not a single lecture relied on Root theory for its scientific basis, even though one lecture did mention the lack of scientific research evidence to support the theories of Root and colleagues.

That being said, I am still indebted to the contributions that Drs. Root, Weed and Orien made to my own knowledge of foot and lower extremity biomechanics and foot orthosis therapy, and to the knowledge base of the international podiatric profession. Their books and teachings on foot and lower extremity biomechanics from nearly four decades ago provided a valuable framework that has allowed the development of better theories of foot biomechanics and improvements in foot orthosis therapy. It is up to the current generation of podiatric researchers to improve on their important body of work for the betterment of our profession and the lives of all of our patients.

—Kevin Kirby, DPM
Adjunct Associate Professor, Department of Applied Biomechanics
California School of Podiatric Medicine, Samuel Merritt University, Oakland, Calif.
Private practice, Sacramento, Calif.

References

1. McPoil TG, Hunt GC. Evaluation and management of foot and ankle disorders: Present problems and future directions. J Orthop Sports Phys Ther. 1995; 21(6):381-388.
2. Root ML, Orien WP, Weed JH. Normal and Abnormal Function of the Foot. Clinical Biomechanics Corp., Los Angeles, 1977.
3. Root ML, Orien WP, Weed JH, RJ Hughes. Biomechanical Examination of the Foot, Volume 1. Clinical Biomechanics Corporation, Los Angeles, 1971.