Prescribing Orthoses: Has Tissue Stress Theory Supplanted Root Theory?

Pages: 36 - 44
Author(s): 
Kevin A. Kirby, DPM

Although the biomechanical theories of Merton Root, DPM, have been accepted in academic circles for decades, this author suggests that the principles of tissue stress theory may help inform more effective orthotic prescriptions.

Custom foot orthoses have been a treatment method for foot and lower extremity pathologies for well over two centuries.

In 1781, Petrus Camper, a Dutch physician, published one of the first books on foot deformities, On the Best Form of Shoe, which stimulated interest in placing arch supporting orthoses into shoes for children’s flatfoot.1 Queen Victoria’s chiropodist, Lewis Durlacher, developed a leather foot orthosis to correct for “plantar pressure lesions” and “foot imbalances” in 1845.2 In 1889, Royal Whitman, MD, developed an orthosis constructed of 18-20 gauge sheet steel made over a plaster cast of a foot in order to raise the medial longitudinal arch of the foot and make it less pronated.3 Edward Reed, MD, an orthopedic surgeon from Santa Monica, Calif., was the first to describe, within the medical literature, plaster splint impression casting for foot orthoses in 1933.4

Then in 1958, Merton Root, DPM, a 1952 graduate from the California College of Chiropody, revolutionized foot orthosis technology by experimenting with new materials called thermoplastics and began developing his Root Functional Orthosis.5 In 1971, Root and colleagues proposed their ideal “eight biophysical criteria for normalcy” and developed a foot and lower extremity classification system that was based on the subtalar joint neutral position.6 They also proposed that all feet and lower extremities that did not meet their criteria for “normal” had structural defects and one should therefore consider these feet “abnormal.”6

In 1971, Root and colleagues also developed the “neutral suspension casting technique” for custom foot orthoses in which they used plaster splints to capture the non-weightbearing contours of the plantar foot while the subtalar joint was in the neutral position and the fourth and fifth metatarsals were dorsiflexed on the rearfoot.7 Finally, in 1977, Root and coworkers published Normal and Abnormal Function of the Foot, their definitive textbook on foot biomechanics and mechanically-based pedal pathologies.8 The book remains an important podiatric textbook to this day.

As a result of his pioneering work in the 1950s, 1960s and 1970s, many consider Root to be the “father of podiatric biomechanics.” Over the past four decades, the ideas and techniques Root proposed have become the best methods by which to evaluate and measure for custom foot orthoses, make impression casts for custom foot orthoses, and design prescription foot orthoses. Until the last two decades, academics were teaching Root’s ideas and techniques as the de facto standard for podiatric biomechanics theory and foot orthosis prescription within the worldwide podiatric profession.

A Closer Look At The Emergence Of Tissue Stress Theory
More recently, however, there has been growing discontent with the biomechanical theories and the orthosis prescription techniques that Root and colleagues first developed over a half-century ago.
In one of the earliest arguments that questioned the validity and wisdom of using the measurement of Root’s “foot deformities” to optimize custom foot orthosis design, Kirby proposed in 1992 that podiatrists should not focus on Root-defined “foot deformities” when designing orthoses for patients.9 He stated that “foot deformity” measurement “does not give us (nearly) enough information to predict the mechanical behavior of the foot and lower extremities during weightbearing activities and, therefore, is insufficient to prescribe the best orthoses for patients.” In addition, he stated that the “magnitude and exact location of pathological tensile, compression or torsional forces on the internal structures are very difficult to predict using the externally measurable parameters such as tibial varum, rearfoot varus, and forefoot to rearfoot relationship.”

Kirby thought that when prescribing foot orthoses, the podiatrist should be “thinking like an engineer.”9 In other words, he felt that once podiatrists “are certain of the various stresses on the structural components, then we can design our mechanical therapy specifically to reduce or eliminate those stresses” rather than designing foot orthoses to prevent “compensation” for Root-defined “foot deformities.”

Three years later, in 1995, McPoil and Hunt also discussed many of the problems they found within the research literature with Root-defined foot biomechanics and foot orthosis theory.10 The authors alternatively proposed using the idea of a “tissue stress model” for prescribing foot orthoses. These authors noted there were problems with the reliability of the measurement techniques that Root advocated and that as a result, Root’s criteria for normal foot alignment were suspect. In addition, they questioned whether the subtalar joint was in the neutral position during walking or not. McPoil and Hunt also noted that using a tissue stress model to prescribe foot orthosis therapy was not a novel idea since the logic of using such an approach was based on the same ideas already currently in use in the treatment of parts of the body other than the foot and ankle.

Furthering the idea of focusing more on internal tissue stress than measuring Root-defined “foot deformities” in 1999, Fuller explained the mechanical significance of the center of pressure relative to the subtalar joint axis.11 In 2000, Fuller discussed how using tissue stress theory could be a tool to better prescribe foot orthoses.12

In 2002, Kirby published three articles that described what he called the “Tissue Stress Approach to Mechanical Foot Therapy.”13 More recently, in 2013, Fuller and Kirby coauthored a mechanical analysis of tissue stress theory.14,15 They explained how one could use subtalar joint axis location and rotational equilibrium theory along with a kinetic analysis of pathological stresses that can occur within the structural components of the foot and lower extremity (i.e. bone, ligament, tendon, muscle, cartilage, fascia and skin) in order to design more effective custom foot orthoses for individuals suffering from mechanically-based pathologies of their feet and lower extremities.

Tissue stress theory relies on the fact that mechanically-based pathologies of the foot and lower extremity all result from pathological magnitudes of stress acting within the structural components of the foot and lower extremity. Stress is an internal measure of how an object resists a loading force and one measures this by dividing the cross-sectional area of that object by the loading force being applied. Stress may be either axial (i.e. compression or tension) or tangential (i.e. shearing) in nature. Compression stress occurs when an object resists being pushed together and tension stress occurs when an object resists being pulled apart. When forces act parallel or tangential to an applied load, one part of an object resists sliding on another part of that object causing a shear stress (see graphic at tleft).

The standard unit of measurement of stress is the pascal (Pa), defined as 1 Newton (N) distributed over 1.0 m2 (1 Pa = 1 N/m2). In scientific studies of tissue mechanics, the megapascal (1 MPa = 1 N/mm2) is the most common unit to measure stress.16

One of the key points in understanding the mechanical nature of tissue injury is that all the body’s tissues exhibit viscoelasticity. Elasticity allows the tissues of the body to return to their original shape once a load is removed. Viscosity causes the tissues of the body to exhibit time-dependent load deformation characteristics that cause strain rate dependency, in which tissues become stiffer the faster they deform.17

In addition, since all the body’s tissues, including bone, are viscoelastic, this means that all the body’s tissues will deform under load with the amount of deformation depending on the magnitude of the loading force. For example, when a ligament has a tension force upon it, it will elongate a small amount under low loads and then return to its original length once that load is removed. However, ligament and tendon will permanently elongate (i.e. undergo plastic deformation) under larger loads and will rupture when under even larger loading forces.

We can quantify the load versus deformation characteristics of all materials, including biological materials, using a stress-strain curve (see the graphic at right). The stress-strain curve of a typical ligament or tendon demonstrates an initial toe region that represents the uncrimping of collagen upon initial loading; a linear region where the ligament or tendon remains elastic and will return to its original shape once the loading force is removed; an elastic limit above the plastic region of the curve where plastic deformation occurs; and a rupture point where the ligament or tendon ruptures.18

Therefore, the key to prevention of tissue injury within the foot and lower extremity is to keep the tissues functioning within their elastic range, where tissue loading forces are small enough during their repetitive loading cycles that patients avoid excessive magnitudes of tissue loading forces that may cause plastic deformation of the tissues and tissue injury during weightbearing activities.10,15,19,20

One example of where the structural components of the foot and lower extremity have plastic deformation and cause painful injury includes the elongation and/or rupture of the posterior tibial tendon in posterior tibial tendon dysfunction (PTTD). In this scenario, the tendon tear itself causes even greater magnitudes of stress in the remaining tendon fibers in the region of the tendon tear (see graphic at left). Other examples of plastic deformation of tissues include the disruption of cortical bone in a stress fracture or complete fracture of a metatarsal and the complete rupture of the anterior talofibular ligament in a grade III inversion ankle sprain. In all of these cases, if the stresses acting within the specific structural component of the foot and lower extremity had remained at lower loads, functioning within the elastic range of its stress-strain curve, then plastic deformation and tissue injury would likely not have occurred.

How Tissue Stress Theory Can Guide Orthotic Prescriptions
With these facts of tissue biomechanics in mind, incorporating tissue stress theory into the design of prescription foot orthosis therapy should enable injured tissues to resume function within the elastic region of their stress-strain curve, reducing the risk of further tissue injury and allowing more prompt tissue healing to occur. The three goals of prescription foot orthosis therapy using tissue stress theory are: reducing the pathological loading forces on the injured structural components of the foot and lower extremity; optimizing overall gait function; and preventing other pathologies from occurring.13,15
In the clinical setting, the podiatrist using tissue stress theory needs to utilize the following steps in order to optimize prescription foot orthosis therapy.13,15

First, specifically identify the anatomical structure that is the source of the patient’s complaints. This requires the podiatrist to have a detailed understanding of foot and lower extremity anatomy, a good understanding of clinical tests and access to diagnostic studies that can help identify which structural component is injured.

Second, the podiatrist needs to determine the structural and/or functional variables that may be the source of the pathological forces acting on the injured structure. A complete history, biomechanical examination of the foot and lower extremity, muscle testing, range of motion examination, and gait evaluation may all be necessary to determine what structural and/or functional variables are the main cause or causes of the excessive stress on the injured anatomical structure.

Finally, formulate a therapeutic treatment plan, including specific foot orthosis modifications, shoe modifications, bracing, stretching, strengthening, physical therapy modalities, injection therapy and surgery. One should carry out this plan in a logical sequence in order to optimize patient healing.

Using tissue stress theory to optimize foot orthosis design for patients with mechanically-based foot and lower extremity pathologies requires podiatrists to have a good appreciation of which anatomical structures are subject to tension, compression and shearing stresses during weightbearing activities. In addition, podiatrists must also understand the various ways that they may alter the design of foot orthoses to lessen the magnitude of abnormal stresses acting within the injured tissues of the foot and lower extremity. In other words, the podiatrist must have a good comprehension of the many variables that may mechanically affect the internal loading forces acting on the external and internal structural components of the foot and lower extremity during weightbearing activities.15

Prescribing Orthoses For Specific Injuries
How might one specifically use tissue stress theory versus Root theory to better design an effective foot orthosis for a patient with a foot or lower extremity injury?

In the case of the common injury of proximal plantar fasciitis, the podiatrist must first be aware of the nature of stresses to which the plantar calcaneus is subject during weightbearing activities. The plantar calcaneus is not only subject to tension forces from the pull of the plantar fascia and plantar intrinsic muscles, but is also subject to compression forces from ground reaction force (GRF). Tissue stress theory dictates that, regardless of whether the patient has a Root-defined rearfoot varus or valgus deformity or a forefoot varus or valgus deformity, the pathological stresses causing the plantar calcaneal symptoms will still remain the same.  

In other words, to treat a patient with proximal plantar fasciitis effectively, the podiatrist doesn’t need to design the prescription foot orthosis using the principles advocated by Root and colleagues. These principles involved “preventing compensation for rearfoot and forefoot deformities,” “causing the subtalar joint (STJ) to function more in the neutral position,” or “locking the midtarsal joint.”13 By using the principles of tissue stress theory, the podiatrist simply needs to design the orthosis to decrease the magnitudes of tension stress and/or compression stress acting on the plantar calcaneus. Possible orthosis modifications may include deep heel cups, well fitting and stiff medial arch contours, padded topcovers and central heel cushioned accommodations within the orthosis heel cup. These modifications should not only reduce the tension stresses acting on the plantar calcaneus from the pull of the plantar fascia and plantar intrinsic muscles, but also reduce the plantar heel compression stresses from ground reaction force acting on the central aspect of the plantar calcaneus (see graphic at right).  

Using tissue stress theory to optimize foot orthosis design for a patient with posterior tibial tendon dysfunction uses the same biomechanical logic. The first step is to identify the injured tissue as the posterior tibial tendon and next realize that the posterior tibial tendon transmits tension forces from the posterior tibial muscle to the insertions of the posterior tibial tendon. One then needs to design the prescription foot orthosis to reduce the pathological tension stress acting within the posterior tibial tendon, improve gait function of the patient and so other pathologies do not occur.  

Patients with posterior tibial tendon dysfunction have varying degrees of medial deviation of the subtalar joint axis. Accordingly, ground reaction force acting on the plantar foot will cause excessive magnitudes of subtalar joint pronation moment in these patients and the posterior tibial tendon will also have a reduced subtalar joint axis supination moment arm (see graphic at left). The result is increased posterior tibial muscle contractile activity and increased posterior tibial tension, which is necessary to counterbalance the excessive subtalar joint pronation moments.14,21-24 Prescription foot orthosis modifications such as the medial heel skive, deep heel cup, inverted balancing position, minimal medial arch fill, stiff orthosis plate material and rigid rearfoot posts are required to increase the subtalar joint supination moment from the orthosis. This will subsequently reduce the need for the posterior tibial muscle to be as active, which will in turn decrease the pathological tension stress acting within the posterior tibial tendon.14,24,25

One of the key concepts of tissue stress theory is that in order to best reduce the stress on the injured tissue, one should design the foot orthosis, when possible, to perform the function of the injured tissue during weightbearing activities. For example, in the case of the patient with proximal plantar fasciitis, the plantar fascia causing a longitudinal arch raising moment needs to have its function duplicated by a custom orthosis made with a well-fitting and supportive longitudinal arch. This orthosis will, like the plantar fascia, also cause a longitudinal arch raising moment on the foot (see graphic at right). In other words, the orthosis needs to perform some of the biomechanical functions of the injured tissue in order to most effectively take the stress off that tissue.

Likewise, in the case of the patient with posterior tibial tendon dysfunction I have described above, a properly constructed foot orthosis needs to have design features that duplicate the function of the posterior tibial muscle. In other words, one must design the foot orthosis to cause a supination moment across the subtalar joint axis. Using modifications such as a medial heel skive, a well formed arch, a stiff orthosis plate and a rigid rearfoot post, the foot orthosis will cause a subtalar joint supination moment. This moment will, by duplicating the subtalar joint supination moment-producing function of the posterior tibial muscle, reduce the tension stress on the posterior tibial tendon.

In summary, we do not need to design effective foot orthoses to “to prevent compensations for foot deformities” or “to realign the foot toward (subtalar joint) neutral” as Root and colleagues advocated. Instead, we should design orthoses by using tissue stress theory simply to reduce pathological stress on injured tissues.

In Conclusion
The medical professions have used foot orthoses for the treatment of mechanically based foot and lower extremity pathologies for over two centuries. During that time, there have been many important individuals who have influenced foot and lower extremity biomechanics theory and foot orthosis design. One of these individuals, Merton Root, DPM, helped develop the modern thermoplastic foot orthosis and proposed theories on foot and lower extremity function and foot orthosis design. Academics have widely taught these theories within the field of podiatric biomechanics over the last four decades.  

However, with the increased knowledge that comes with better research and better biomechanical theory, it is now obvious that many of Dr. Root’s evaluation and treatment methods need refinement, and even replacement, in order to give the best treatment results to our patients. Reevaluating Dr. Root’s methods may also allow podiatrists to stay at the leading edge of prescription foot orthosis theory and practice in the increasingly competitive medical marketplace. Tissue stress theory is currently the best method by which to design prescription foot orthoses for patients with mechanically based foot and lower extremity pathologies. 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 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.     Camper P. On the Best Form of Shoe. Translated in: Dowie J. The Foot and Its Covering. Hardwicke, London, 1861.
  2.     Durlacher L. A Concise Treatise on Corns, Bunions, and the Disorders of Nails with Advice for the General Management of the Feet. Simpkin, Marshall and Co, London, 1845.
  3.     Whitman R. Observations of forty-five cases of flat-foot with particular reference to etiology and treatment. Trans Am Orthop Assoc. 1889; 11(1):122-137.
  4.     Reed EN. A simple method for making plaster casts of feet. J Bone Joint Surg. 1933; 17:1007.
  5.     Root ML. How was the Root functional orthotic developed? Podiatry Arts Lab Newsletter, Pekin, Illinois, Fall 1981.
  6.     Root ML, Orien WP, Weed JH, Hughes RJ. Biomechanical Examination of the Foot, Volume 1. Clinical Biomechanics Corporation, Los Angeles, 1971.
  7.     Root ML, Weed JH, Orien WP. Neutral Position Casting Techniques. Clinical Biomechanics Corp., Los Angeles, 1971.
  8.     Root ML, Orien WP, Weed JH. Normal and Abnormal Function of the Foot. Clinical Biomechanics Corp., Los Angeles, CA, 1977.
  9.     Kirby KA. Foot and Lower Extremity Biomechanics: A Ten Year Collection of Precision Intricast Newsletters. Precision Intricast, Inc, Payson, AZ, 1997, pp. 267-268.
  10.     McPoil TG, Hunt GC. Evaluation and management of foot and ankle disorders: Present problems and future directions. JOSPT. 1995; 21(6):381-388.
  11.     Fuller EA. Center of pressure and its theoretical relationship to foot pathology. J Am Podiatr Med Assoc. 1999; 89(6):278-291.
  12.     Fuller EA. Reinventing biomechanics. Podiatry Today. 2000; 13(7):30-36.
  13.     Kirby KA. Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002, pp. 11-18.
  14.     Kirby KA. Subtalar joint axis location and rotational equilibrium theory of foot function. J Am Podiatr Med Assoc. 2001; 91(9):465-488.
  15.     Fuller EA, Kirby KA. Subtalar joint equilibrium and tissue stress approach to biomechanical therapy of the foot and lower extremity. In Albert SF, Curran SA (eds): Biomechanics of the Lower Extremity: Theory and Practice, Volume 1.  Bipedmed, LLC, Denver, 2013, pp. 205-264.
  16.     Whiting WC, Zernicke RF. Biomechanics of Musculoskeletal Injury, Second Edition. Human Kinetics, Champaign, IL, 2008, p. 81.
  17.     Whiting WC, Zernicke RF. Biomechanics of Musculoskeletal Injury, Second Edition. Human Kinetics, Champaign, IL, 2008, pp. 90-91.
  18.     Whiting WC, Zernicke RF. Biomechanics of Musculoskeletal Injury, Second Edition. Human Kinetics, Champaign, IL, 2008, pp. 83-84.
  19.     Kirby KA. Foot and Lower Extremity Biomechanics III: Precision Intricast Newsletters, 2002-2008. Precision Intricast, Inc., Payson, AZ, 2009, pp. 17-20.
  20.     Kirby KA. Foot and Lower Extremity Biomechanics IV: Precision Intricast Newsletters, 2009-2013. Precision Intricast, Inc., Payson, AZ, 2014, pp. 7-8.
  21.     Kirby KA. Methods for determination of positional variations in the subtalar joint axis. J Am Podiatr Med Assoc. 1987; 77(5):228-234.
  22.     Kirby KA. Rotational equilibrium across the subtalar joint axis. J Am Podiatr Med Assoc. 1989; 79(1):1-14.
  23.     Kirby KA. Biomechanics of the normal and abnormal foot. J Am Podiatr Med Assoc. 2000; 90(1):30-34.
  24.     Kirby KA. Conservative treatment of posterior tibial dysfunction. Podiatry Management. 2000; 19:73-82.
  25.     Kirby KA. The medial heel skive technique: improving pronation control in foot orthoses. J Am Podiatr Med Assoc. 1992; 82(4):177-188.

 

Comments

It appears that instead of making an orthosis based on Root theory and adding accommodations based on pathology, the author is taking a cast using Root principles and adding accommodations based on pathology and saying it is due to forces.
The author states, "In other words, one must design the foot orthosis to cause a supination moment across the subtalar joint axis. Using modifications such as a medial heel skive, a well formed arch, a stiff orthosis plate and a rigid rearfoot post, the foot orthosis will cause a subtalar joint supination moment". Nowhere does he state that how he can make the orthosis vary the forces with this modification. However, he does state using a rearfoot post, which begs the question, how many degrees is this post and how does he determine it?

Thank you for the comments and questions regarding my article. Tissue Stress Theory does use some components of the teachings of Dr. Root and colleagues. As for myself, I was very strongly influenced by the teachings of Dr. Root and his colleagues and do feel that I have benefited from their influence on my thinking and on how Tissue Stress Theory is currently being taught. I actually taught Root Theory when I was a Biomechanics Fellow at CCPM from 1984-1985 and still use many of the concepts taught to me by Dr. Root and his colleagues in my podiatric practice.

The main difference between Root Theory and Tissue Stress Theory when it comes to designing and prescribing custom foot orthoses for patients that have mechanically-based foot and/or lower extremity pathologies is that Root Theory orthoses are nearly always prescribed with the heel balanced vertical and are designed with the goal to make the foot function toward the subtalar joint neutral position whereas Tissue Stress Theory orthoses are designed with the specific goal of reducing the pathological stress on the injured tissue without causing injury elsewhere.

That being said, Root Theory and Tissue Stress Theory do share common features in many instances. In some patients, foot orthoses made using each theory may be nearly identical in structure. However, there are other instances where Root Theory and Tissue Stress Theory produce very different foot orthoses since the goals of the two theories are quite different from each other.

As to the specific design variables such as the medial heel skive (Kirby KA: The medial heel skive technique: improving pronation control in foot orthoses. JAPMA, 82: 177-188, 1992.), stiff orthosis plate, rigid rearfoot posts and rearfoot post variables, this was beyond the scope of my article on Tissue Stress Theory in Podiatry Today Magazine. I have, however, lectured and written extensively on the specifics of foot orthosis design for the many foot and lower extremity pathologies seen commonly by podiatrists, including in-detail discussions of the biomechanics of these specific orthosis designs within the pages of my four published books. These books should provide the reader a better perspective as to why specific orthosis modifications are ordered for each foot and lower extremity mechanically-based pathology using Tissue Stress Theory, and in much greater detail then I possibly can here.

Kirby KA: Foot and Lower Extremity Biomechanics: A Ten Year Collection of Precision Intricast Newsletters. Precision Intricast, Inc., Payson, Arizona, 1997.

Kirby KA: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002.

Kirby KA: Foot and Lower Extremity Biomechanics III: Precision Intricast Newsletters, 2002-2008. Precision Intricast, Inc., Payson, AZ, 2009.

Kirby KA: Foot and Lower Extremity Biomechanics IV: Precision Intricast Newsletters, 2009-2013. Precision Intricast, Inc., Payson, AZ, 2014.

It would appear that the author is stating the symptoms dictate whether or not the prescriber should use a particular type of accommodation or orthotic modification in creating the dispensed orthotic. I thought that was why Dr. Root developed the Root principles approach to designing his orthotics. He tried to envision what pathology was introducing the forces that were inducing the patients complaints. Thus his symptomatic approach to orthotic design to minimize the forces causing the patient's complaints based upon the individual foot design.

If Tissue Stress Theory has supplanted Root-ian Biomechanics, it is fair to say that we as a profession have failed to discover how the foot actually works as a whole along with its individual components. Tissue Stress Theory takes us back to the old 'bag of tricks' method. If we return to the old approach, I am having trouble understanding how this unifies the profession and keeps us at the leading edge of foot care. Tissue Stress Theory is having to be shouted and touted as the best there has ever been by its creator, and not the profession in general, almost thirteen years after having been introduced. It has yet to become any sort of standard after indoctrination of class after graduating class, at the collegiate level.
What does that say about the theory? It says just that. Still a theory without proof nor consistency in results.

Thank you for your comments regarding my article, Dr. Jones. Yes, you are correct that tissue stress theory is based on the fact that in order to optimize the therapeutic effect of custom foot orthoses, the orthosis must be designed to decrease the pathologic loading forces on the injured structural component of the foot and/or lower extremity, whether that tissue is bone, cartilage, ligament, muscle, tendon, fascia or skin. This is opposed to the principles that Dr. Root taught for many years at the California College of Podiatric Medicine (CCPM) where foot orthoses were not designed to treat specific pathologies, but were rather designed to “prevent compensation for foot deformities”, “hold the subtalar joint closer to neutral position”, and “lock the midtarsal joint”.

Not only did I attend many of Dr. Root’s lectures as a Biomechanics Fellow at CCPM and in my early years of podiatric practice in the 1980s, I was also chosen by Dr. Root to be one of the handful of podiatrists who were to help him edit his next book. In addition, I spent a summer writing a workbook for John Weed, DPM, between my second and third years as a podiatry student at CCPM along with Kirk Koepsel, DPM, a classmate of mine. I also taught Root biomechanics as the Biomechanics Fellow at CCPM to third- and fourth-year podiatry students from 1984-1985.  So, Dr. Jones, I really don’t know where you are getting your information from regarding how Root theory was taught during the 1970s and 1980s, but it certainly wasn’t being taught as a “symptomatic approach to orthotic design” as you claim. 

Rather, it is a fact, the orthosis prescription protocol taught as Root theory focused on treating “foot deformities”, not on treating the patient’s symptomatic complaints. Therefore, regardless of whether the patient suffered from plantar fasciitis, posterior tibial tendinitis, peroneal tendonitis, sesamoiditis, pes anserinus bursitis, medial tibial stress syndrome, patello-femoral syndrome, iliotibial band syndrome, or 2nd metatarsophalangeal capsulitis, to name a few pathologies, the Root theory orthosis prescription protocol  revolved largely on the line drawn on the posterior surface of the calcaneus and whether that line, the “calcaneal bisection,” could come to vertical (i.e. “fully compensate to vertical”) or not. From what I learned as a student, a Biomechanics Fellow, and attending Dr. Root’s lectures, Root theory did not alter orthosis prescription protocol for a different anatomical location of symptoms but rather would alter orthosis prescription based on “foot deformities” and would nearly always recommend balancing the calcaneus vertical to make the orthosis.

In addition, Root theory did not advocate the fact that foot orthoses should often have forefoot extensions which are commonly used now and were fairly commonplace on the East Coast under the influence of the teachings of Richard Schuster, DPM. Root theory rather taught that the vast majority of foot orthoses should be made with vertically balanced heel, have a 4 degree/4 degree rearfoot post, have an intrinsic forefoot correction and have no forefoot extensions. Therefore, Dr. Jones, unless you or anyone else can produce evidence to the contrary, your claim that Dr. Root’s approach was a “symptomatic approach to orthotic design”, demonstrates to me that you are misinformed as to what Dr. Root actually taught during his seminars and during his tenure as a Biomechanics Professor and Chairman at CCPM.

Also, Dr. Jones, I have no clue what you mean by saying that “tissue stress theory takes us back to the old 'bag of tricks' method”. Rather, Dr. Jones, contrary to your unusual and unsupported statement, tissue stress theory uses the modern biomechanics principles of tissue stress, external and internal loading forces and moments, viscoelasticity, modelling and free-body diagram analysis to ascertain how best to modify custom or pre-made foot orthoses in order to accomplish the orthosis goals of 1) decreasing the pathologic forces acting on the injured structural components of the foot and lower extremity, 2) optimizing gait function and 3) preventing other pathologies from occurring. I would suggest, Dr. Jones,  that you should read the recent 60-page book chapter I coauthored along with Eric Fuller, DPM, which may help clear some of your misunderstandings about tissue stress theory (Fuller EA, Kirby KA:  Subtalar joint equilibrium and tissue stress approach to biomechanical therapy of the foot and lower extremity.  In Albert SF, Curran SA (eds): Biomechanics of the Lower Extremity:  Theory and Practice, Volume 1.  Bipedmed, LLC, Denver, 2013, pp. 205-264). 

Finally, Dr. Jones, I also find it odd that you go on to state “tissue stress theory is having to be shouted and touted as the best there has ever been by its creator, and not the profession in general, almost thirteen years after having been introduced. It has yet to become any sort of standard after indoctrination of class after graduating class, at the collegiate level.”  Certainly, Dr. Jones, I know that you also recently introduced a theory called “Wring Theory” on your website https://wringtheory.wordpress.com/2012/10/06/wring-theory-old-biomechanics-with-a-new-twist/  and that you know that your theory, even though introduced years ago, has also not become any sort of standard within the podiatric profession. I suggest rather than us publicly criticizing the author of a theory, we instead let the podiatric profession as a whole decide which of our theories is best and let history decide which of our theories will stand the test of time and gain wide acceptance within the worldwide podiatric profession.

Kevin A. Kirby, DPM

Adjunct Associate Professor

Department of Applied Biomechanics

California School of Podiatric Medicine

I have read Dr. Kirby’s article, Dr. Jones' comments and Dr. Kirby’s reply. I have known both of these fine doctors for many years. I am disappointed that overt and subtle personal attacks are made in this exchange, which really should focus only on the subject matter.

Dr. Kirby graduated only a handful of years after me, having most of the same professors that I had at CCPM. I had the opportunity to teach Dr. Jones as a student at Des Moines University and have had occasional contact with him since. I think that Dr. Jones is questioning the newness of tissue stress because he will find in my lecture notes from when he was a student in the early 1990s, a lot of information about tissue stress principles and their applications. Since many consider me a Root disciple, they may believe that most of my lecture notes are purely Root’s lectures.

Dr. Kirby falls back on personal experience to present himself as the foremost authority of what constitutes Root theory. After my graduation from CCPM in 1979, in the first few years I had only occasional contacts with Dr. Root, but as the years went on, I had more and more contact with him. Unfortunately, I quickly found, after graduation, that my training in biomechanics did not give me adequate resources to read the Journal of Biomechanics. As a result, I found myself studying many other books of biomechanics and mathematics. The principles of tissue mechanics is a mainstay of most college textbooks of biomechanics. A book that markedly influenced me was “Tendinitis: Its Etiology and Treatment” by Curwin and Stanish, ©1984. There is nothing in this book about joint kinesiology or kinematics. It bases its analysis and treatment in understanding the viscoelastic properties of tendons.

Dr. Kirby presents himself as teaching Root principles at CCPM in the early 1980s, and he would have us believe that those principles were the only and final Root principles. At the same time he was doing this teaching, I was also communicating with Dr. Root on work I was doing and he was kind enough to review papers that I published in 1983 and in 1985 on the forefoot to rearfoot relationship and also on better determining the subtalar joint axis orientation. So at the time of Dr. Kirby’s teaching, Dr. Root continued to encourage others to carry forward with new principles, and learned new things himself. Therefore, I do not believe that Root can be thought of as a dogmatic static individual who was not open to change and develop new ideas.

When Dr. Jones refers to “an old bag of tricks,” I have to be somewhat in agreement, though I would not have used that phrase. I do see that those advocating that only “tissue stress is necessary” have taken a step backward in that they only are interested in treating symptoms after they occur. There certainly has been much criticism of “Root Principles” in the literature, from reliability of measurement to subtalar joint neutral to casting and to whether “Root Custom Orthotics” are better than over-the-counter devices. Despite these controversies, I still find in Root more of a vision that it is possible to prevent problems. I do agree with the tissue advocates that it is important to diagnose whether symptoms are being produced by abnormal tension, compression or shear, and that all shoe inserts need to be customized to counter those abnormal forces. I believe that Paul Scherer, DPM, tried to better explain this in his latest book. However I would contend that this is something new. As a 1979 graduate of CCPM, I seemed to have learned this concept somewhere in my education, though I can’t say exactly where or how. Certainly, taking a standard history taking and performing a physical examination is not something new. Why is trying to analyze the abnormal forces somethings new? It certainly seemed to be taught in the 1970s. I believe that somehow there were individuals who in making the student syllabus of seemed to focus on certain Root teachings that then were used to make their syllabus of biomechanics teachings, that made them think that they were teaching everything Root believed. And certainly when Root publicly taught, he may have focused on the principles that he thought were not commonly not understood or accepted.

As I expressed above, I believe that the biggest contribution of Root was his vision of what could be — that we could not only understand the forces that were causing pathology, but also understand the abnormal motions (or failure of motions) to understand the creation of those abnormal forces, and then take it further and understand the etiology of the abnormal motions and/or the reason why normal motions did not occur. What I find lacking in any of the discussion of stress theory is much discussion of why abnormal motions (or failure of motions) occur. The only discussion of etiology of abnormal motions seems to be the projection of the subtalar joint axis onto the plantar surface of the foot. This writer will not underestimate the importance of the subtalar joint axis location but nowhere do I see discussion of the forefoot to rearfoot relationship, nor discussion of forefoot compensation for abnormal rearfoot motion. What I find lacking in the new tissue stress advocacy are principles that can better predict pathology. Clinical methods being advocated are directed to non-quantitative assessments, which I believe is a step backward from the vision of Root of clinical quantitative assessments. Of course, very high-priced biomechanical laboratories can crank out quantitative moments, but these are not clinical tools readily available to the average practitioner.

This writer is grateful that Dr. Kirby has taken it upon himself to further educate the profession on time-proven principles of material mechanics and their application to the podiatric profession. This is not a new theory, only a new focus. The principles he discusses, while in the textbooks for many years in their basic forms, are little thought of by most podiatric physicians, and this needs to change if podiatry is to continue to be at the forefront of treating mechanical disorders of the foot. Failure to understand these principles will only result in further deterioration of our claim as the true experts in foot mechanics. I see a great problem with the idea that we don’t need a neutral subtalar joint position, or that we don’t need to measure a forefoot to rearfoot relationship if we have tissue stress principles. I find that utilizing all biomechanical principles in concert, tissue stress principles, twisted plate principles, functional hallux limitus principles, subtalar neutral principles, etc., can help us be the best clinicians, and also further the research and development of mechanical foot theory and treatment.

Sincerely,
Robert D. Phillips, DPM
Orlando VAMC

Disclaimer: The opinions of the writer are his alone, and do not portend to represent the opinions of the U.S. Department of Veterans Affairs, nor any other agency or individual of the United States government.

Thank you, Dr. Phillips. I believe you covered the issue at hand very well. I know many fellow clinicians that share similar insights. Thank you for taking the time to address this so well.
Paul Jones, DPM

Thanks to Dr. Phillips for his comments on my article.  Dr. Phillips and I have known each other and lectured with other for the past three decades. However, it is important that some of his statements are discussed further to add more clarity and accuracy to these issues.

First of all, Dr. Phillips states that I had somehow presented myself “as the foremost authority of what constitutes Root theory”. Nowhere in my article published in the April 2015 issue of Podiatry Today or in my comments following the article did I make such a claim. Since Dr. Phillips opened up his comments by stating that he was “disappointed that overt and subtle personal attacks are made in this exchange, which really should focus only on the subject matter”, then I find it surprising that Dr. Phillips himself opens up his comments by misstating and exaggerating what I actually wrote instead of “focusing on the subject matter”, as he admonished me to do.

As I stated in an earlier comment, I was taught Root biomechanics at CCPM from 1979-1983 as a podiatry student, and taught Root biomechanics as a Biomechanics Fellow from 1984-1985. In addition, I attended many Root seminars where Dr. Root, Dr. Weed and Dr. Orien lectured. I also worked very closely with Dr. Weed on class projects and spoke with him weekly during my Biomechanics Fellowship.  In other words, I was also, like Dr. Phillips, a Root disciple during my Biomechanics Fellowship since I taught Root Theory to podiatry students and used Root orthosis prescription techniques in nearly all of the orthoses I made for my own patients.

However, during my CCPM Biomechanics Fellowship, I started to note a distinct set of problems with the Root Theory that was being taught at CCPM. First of all, the determination of calcaneal bisections by clinicians and students was highly variable, being +/- 5 degrees among the CCPM Biomechanics Professors and being +/- 10 degrees among graduating senior podiatry students. Secondly, I also noted during my Biomechanics Fellowship that the determination of subtalar joint neutral and of the forefoot to rearfoot relationship was variable from one clinician to another and especially from one graduating senior podiatry student to another. Third, I noticed that the Root-inspired measurements we performed had a poor predictive value of either gait function or of the patient’s pathology. These observations I made over three decades ago as a Biomechanics Fellow have since been confirmed as being accurate within the scientific research literature.

Since these Root measurements, which were used as the sole determinants of how foot orthoses should be balanced and constructed according to Root Theory, had so much inter-observer error, my clinical observations left me with more questions than answers in trying to rectify Root Theory to reality. In other words, in my search for theoretically coherent biomechanical answers as to how foot orthoses functioned and how foot orthoses should best be ordered, Root Theory did not make sense. It seemed obvious to me at the time that if the CCPM Biomechanics professors couldn’t all agree on how to bisect a calcaneus, then how could we expect a senior podiatry student with only three months of biomechanics training to use Root-inspired evaluation techniques to accurately prescribe foot orthoses? The answer was we couldn’t.

Dr. Phillips goes on to state in his commetns that “I do not believe that Root can be thought of as a dogmatic static individual who was not open to change and develop new ideas.”  While I agree that Dr. Root’s teachings did change slightly over the 10+ years that I heard him lecture, I will disagree that Dr. Root was open to change or to new ideas, at least from me.

One such instance comes to mind that is still as vivid today as when it happened 30 years ago. In a lecture I attended given by Dr. Root when I was at the end of my Biomechanics Fellowship, I asked Dr. Root, during the lecture, how he could be so sure that there were not inherent inaccuracies in the calcaneal bisection technique he advocated where I had found the range of error in calcaneal bisections by the CCPM Biomechanics Professors to be +/- 5 degrees.

In the ensuing and lively next five minutes, Dr. Root told me and the rest of the audience, in an ever increasingly raised voice that “even a monkey could be trained to draw a calcaneal bisection accurately."  Dr. Root further stated that since he had left CCPM as a faculty and professor that he had no control over what was taught at CCPM. As I sank further and further into my seat in the back of the meeting room during Dr. Root’s scolding [I thought I asked a perfectly valid scientific question], it certainly wasn’t my impression that Dr. Root was open to change, especially any questions that challenged his dogma coming from a 28 year-old Biomechanics Fellow who was 35 years his junior.

That being said, I still consider that Drs. Merton Root, John Weed, Ronald Valmassy and the rest of  my Biomechanics Professors at CCPM to be my most valuable teachers while I was a student and Biomechanics Fellow at CCPM. I learned an immense amount of information from all of these fine individuals. In fact, I still teach much of what I learned from them, even now, 30 years later.

However, unlike many others during that time, I have also not felt any obligation to simply parrot back theories of foot function and/or orthosis prescription to the students, residents and clinicians I have taught because I greatly admired the originator of those theories. Rather, I felt it was my obligation to attempt to elevate the foundation of knowledge that Dr. Root and his coworkers laid down for me, and for my podiatric colleagues, in their quest to improve the lives of patients who suffered from mechanically-based foot and lower extremity pathologies.

Thank you, Dr. Root, for doing all of what you did for me, and for the podiatry profession.

Kevin A. Kirby, DPM

Adjunct Associate Professor

Department of Applied Biomechanics

California School of Podiatric Medicine

Private Practice, Sacramento, California

As an unlikely contributor to this forum, it seems appropriate that I begin by presenting why I am uniquely qualified to opine here, on this particular topic, and especially since there’s a certain amount of orthotic utilization history already presented and commented on in this thread. I have been a peripheral student of podiatric biomechanics since 1980, not by way of formal enrollment at any professional school, but by way of experience in fabricating and supplying custom foot orthoses to the profession for over thirty years.

My informal training began with my employment at Langer Biomechanics (known then as Langer Orthotic Laboratory) under the personal tutelage of Drs. Justin Wernick, Sheldon Langer and Glenn Ocker. But, it was the region in California where I worked for them that facilitated my direct encounters with Drs. Root, Weed, Sgarlato, Subotnic, Hlavac, Valmassy, Blake, Kosai, Morris, Scherer, Berenter and initially as a biomechanics resident at CCPM, Dr. Kevin Kirby. For those of you readers in the western states who ever inquired about the EDG, we either met or at the very least had a conversation at some point.

I make my observation here because I submit that the Tissue Stress Theory de facto supplanted the Root Foot Morphology theory many years ago, only because many fabricators of foot orthoses realized the impracticality of “balancing the foot/cast” to achieve a vertical calcaneus in each and every case. My first realization came when confronted with an actual bilateral twenty degree forefoot varus. The process of adding a plaster posting platform to achieve a vertical calcaneus resulted in a drop of over an inch behind the 1st met head. If you were to stick to conventional Root cast preparation technique, there would be no break-in period long enough before a patient could tolerate wearing those devices, especially since Rohadur was the preferred material for modules back then. So laboratories turned to deliberating over how much correction could the patient tolerate and still achieve effective treatment? In other words, how much supinatory influence (moment arm force) could be applied to produce less stress on the injured tissue?

A second realization that what we were applying was Ground Reactive Force to specific components of the foot to control resultant motions and not filling in under a “deformity” to establish a vertical calcaneus on a plaster cast, whether it be rearfoot or forefoot. This was when a cogent description of forefoot supinatus developed. If the inverted forefoot malalignment was being held in place by plastic deformation of ligaments, then what imbalance of forces caused the rearfoot to repetitively evert and the forefoot to invert? And then, which component of the orthosis should be employed to control for that imbalance? This was the point where Drs. Wernick and Langer had implemented their method for remodeling positive casts by filing away from the lateral side, instead of posting up the medial side, to illicit a pronatory moment around the LMJA by relative dorsiflexion of the lateral column, in what Dr. Jones now attempts to describe as “wringing” the foot with a twisted plate.

Over the years, I have read all of Dr. Kirby’s volumes on Lower Extremity Biomechanics, all his articles, journal or otherwise, that I could locate and Drs. Phillips’, Anthony’s and Valmassy’s, amongst others, bound text on foot function and applying custom formed orthotic devices. Too many times, the rote formulas for modifying positive foot models and “posting” orthotic modules didn’t produce the intended outcome. So, either you continue doing the same thing over again and again, or you modify your approach to produce a beneficial product. It wasn’t until Dr. Kirby proposed his Balance Equilibrium Theory that what we knew was effective had a rationale for its usefulness. It was at that point we became aware of how implementing this method of redirecting of GRF had a theoretical name to it.

And about this same time, articles in refereed journals were showing a lack of statistical correlation to Root’s foot classifications and accurate prediction of dysfunction. We were again reassured by the method we had previously adopted. It’s not that the foot morphology theory had been entirely discredited. It was that there were reasons for what happened when it didn’t work out as expected. We had operated by using it with enough success to develop thriving enterprises throughout the country. So there was merit in its application.

My assessment of foot shape/deformity relative to functional anomalies in gait is: your shape is a set congenital alignment. How you adapt, or to use Dr. Root’s vernacular, “compensate”, to your shape in order to achieve over ground locomotion is not predictable based exclusively on shape. The deformities are there. How you react to them is an individual endeavor that involves mechanical linkages regulated by sensory motor integration of muscular activity. And if we were all able to produce the same level of kinesthetic interaction, I could have given Michael Jordan a run for his money.

It was Dr. Kirby’s demonstration of how achieving balance equilibrium of forces around joint axes, albeit mostly focused on the STJ, will relieve excessive forces that lead to repetitive stress/strain reactions in the foot. Applying the Tissue Stress Theory means identifying which foot movements are excessive or inadequate to maintain healthy forces on not only the foot, but the entire kinetic chain. That there is not a checklist of biomechanical tests, with or without the use of sophisticated instrumentation, proven reliable for determining how much force or where to apply GRF specifically does not mean there are not worthy observations in each individual case that will help predict the benefit of utilizing a foot orthosis to manipulate segmental movements.

It’s not necessary to achieve equilibrium in every case. Moving a segment away from an excessive force imbalance may be all that is required to allow the patient to develop an alternate gait pattern that is less destructive to the involved structure(s), allowing for healing. Dr. Kirby has described several tests in his various texts, assessing for a deviated STJ axis being one of them, supination resistance test being another. There are also other authors with tests to reliably determine the effectiveness of certain orthotic components for midtarsal joint and first ray stability as well, maybe not using Tissue Stress Theory by name but evoking the same principle. And a rose by any other name is still the same.

If you are still relying only on the Foot Morphology model for making orthotic prescriptions, I would recommend integrating the Tissue Stress Theory incrementally, first by adding Dr. Kirby’s STJ axis location assessment technique. I would also encourage some simple weightbearing tests to challenge the linkage system at specific segments, such as lunges for rearfoot to midfoot linkage integrity, heel raises for first ray stability assessment, single and double limb half squats for rearfoot motion confirmation, limb rotation and trunk rotation for knee to rearfoot and hip to rearfoot linkage integration. And, if you are not watching your patients walk barefoot, you are doing yourself and them a disservice. Just because it looks like it would function one way in an off weightbearing examination doesn’t mean that is how it will be exhibited in gait. Patients have a way of adapting to biomechanical challenges in unpredictable ways.

Using stress challenge tests to accentuate destructive movement patterns will illicit discomfort, or at least expose poor sensory motor integration, directing you to those segments or linkages in the foot that are not stable, mobile or are functionally ineffective under increased load. Having that knowledge can direct you to orthotic components to control for those destructive joint moments. By applying an appropriate orthotic module with specific components to address force imbalances, you will likely make not only the foot more functionally efficient, but the entire human locomotor linkage system more efficient in the process as well.

Respectfully submitted,

Greg Wolfe, C.Ped., BOCPD
President, Biomechanical Services Inc.

What is Root Theory? Merton L. Root, DPM had many theories. Much of Root’s work was made possible due to his theory of the neutral position of the subtalar joint. Root recognized that if the foot could become supinated and pronated at the subtalar joint, then there must be a transitional point at which the foot was neither supinated nor pronated. He called this the neutral position of the subtalar joint. He utilized this neutral position as a standard position in which to compare feet. He also placed the midtarsal joint in a fully pronated position when comparing feet.

Root developed a very specific technique for bisecting the posterior surface of the calcaneus (rearfoot) which he described in his book Biomechanical Examination of the Foot. He developed a number of techniques for examining the foot and lower extremity that he also described in this book. Using all of these concepts, he was able to classify over twenty osseous conditions of the foot, including forefoot varus, forefoot valgus, rearfoot varus and rearfoot valgus. He also described single ray conditions such as a plantar flexed 1st ray and metatarsus primus elevatus based on his standard position of anatomical evaluation. Positional changes at the major and minor joints of the foot alter the relative position or relationship of the osseous segments of the foot. As a result of Root’s system of morphological classification of the foot, clinicians are able to discuss structure and structural variations in a much more meaningful manner.

Root also developed theories of foot function. He theorized how individual osseous conditions might influence function of the foot during static stance and during locomotion. He described how muscles and ligaments might be affected by certain osseous conditions or positions of the foot. For example, he theorized how a plantarflexed 1st ray might respond to ground reaction force. Root’s theories of compensation were described in detail in his third and final book Normal and Abnormal Function of the Foot by Root, Weed and Orien.

Root also developed the neutral position casting technique and a pronated version for certain pathology. Through trial and error, he determined that placing the midtarsal joint in a fully pronated position during casing produced even better outcomes. He also developed and named the Functional Orthotic, which later became known as the Root Type Functional Orthotic as more and more orthotic variations became available. Root’s suspension casting technique, positive cast modification technique and functional orthosis are in common use today, and are the foundation of the modern day foot orthotic.

It is only logical that time has enabled enhancements of Root’s original design, such as functional orthoses with medial heel skives or more highly inverted devices such as the Blake Functional Orthosis. In addition, new methods of examination and diagnosis have been developed and refined such as the Hubscher maneuver or Kirby’s subtalar joint axis location technique. In the introduction to Normal and Abnormal Function of the Foot, Root wrote “The practitioner must have the best possible basis on which to make treatment decisions. He cannot wait until sufficient research has been conducted to conclusively prove how the foot functions.” I would contend that those basing treatment decisions on proof alone will have a very limited scope of practice and will be missing out on the opportunity to help many in spite of insufficient evidence.

Supplant means to take the place of or substitute for. Has Tissue Stress Theory supplanted Root’s work? Obviously not, especially since those that profess to practice tissue stress theory also employ a number of Root-based theories, concepts and techniques. It would be more accurate to say that Tissue Stress Theory augments “Root Theory”. Unfortunately labels like Root Theory and Tissue Stress Theory may act to impede progress in lower extremity biomechanics and custom foot orthotic therapy because they are gross generalizations of some of the fundamental biomechanical principles of these supposed individual theories. In reality, there is significant overlap here. Can a traditional Root type Functional Orthosis alter tissue stress? Absolutely. And can an orthosis made with the Tissue Stress approach alter osseous position or influence compensation? Absolutely.

Where do we go from here? We need better and more clearly defined biomechanical examination techniques and treatment practices. We need biomechanical models that apply to surgical and non-surgical treatment of pathology. We need commonly accepted and clearly defined terminology to describe motion, position, structure and deformity. What we don’t need is ambiguous labels like Root Theory and Tissue Stress Theory that divide groups into firmly entrenched camps and as a result, impede progress. As Daryl Phillips, DPM, so eloquently put it in a recent lecture slide, there is no such thing as Root Theory or Tissue Stress Theory, there is only biomechanics!

Jeff Root
President, Root Laboratory

Thanks to Jeff Root for commenting on my article "Prescribing Orthoses: Has Tissue Stress Theory Supplanted Root Theory?" Jeff brought to light the many accomplishments that his father, Merton Root, DPM, made for the podiatry profession. While it is true that the term "Root Theory" may mean different things to different people, in regard to my article, the Root Theory that I was discussing was Dr. Root's very specific method of prescribing foot orthoses based on "foot deformities".

As many of those who were trained at the California College of Podiatric Medicine (CCPM) by the biomechanics faculty at CCPM, all of who had been students of Dr. Root, foot orthosis prescription protocol was not taught at all like we currently teach using Tissue Stress Theory. Using Dr. Root's orthosis prescription protocol that was being taught at CCPM during the 1970s and 1980s, if a patient had a rearfoot varus deformity and pronated to the heel vertical position in relaxed calcaneal stance position (RCSP), then he or she would receive a Rohadur orthosis, balanced with the heel vertical, without a topcover, without a forefoot extension and with or without a 4 degree/4 degree rearfoot post. This orthosis prescription would be used for all patients with this "fully compensated rearfoot varus deformity" under the Root orthosis prescription protocol regardless of whether the patient had plantar fasciitis, patellofemoral syndrome, medial tibial stress syndrome, sesamoiditis, Morton's neuroma, peroneal tendinopathy, posterior tibial tendinitis, or any other injury to their foot and lower extremity. In other words, the Root orthosis prescription protocol was based on calcaneal bisections and whether this calcaneal bisection could come to vertical or not in RCSP.  

Even though Dr. Root never specifically published his protocol, I was fully aware of Dr. Root's foot orthosis prescription protocol since I was the only Biomechanics Fellow at CCPM from 1984-1985 and had attended many of Dr. Root's seminars, and was in very close communication with John Weed, DPM, about this orthosis prescription protocol on a weekly basis during my biomechanics fellowship. Probably the best published description of the Root foot orthosis prescription protocol was written by UK podiatrist Raymond J. Anthony in his book, The Manufacture and Use of the Functional Foot Orthosis, published in 1991 by Karger.

Even there may be some similarities of the foot orthosis prescribed using the Root Functional Foot Orthosis protocol (that myself and thousands of other podiatrists were taught as students at CCPM during the 1970s and 1980s) and the tissue stress approach, the main difference between the two approaches is that in the tissue stress approach, the prime focus is the anatomical location of pathology that the patient presents to the podiatrist with, not their "foot deformity" and not where their heel bisection is during RCSP as emphasized by Dr. Root in his orthosis prescription protocol.  

In other words, if there were two patients, both with a "3 degree rearfoot varus deformity that pronated to heel vertical in RCSP", but one had posterior tibial tendinitis/tendinopathy and the other one had a peroneal tendinitis/tendinopathy, Dr. Root taught that the orthoses for these two patients with very different anatomical locations for injuries should have identical orthoses made for them. However, in tissue stress theory, the "3 degree rearfoot varus deformity that pronated to heel vertical in RCSP" is ignored and the orthosis, instead of being designed to "prevent compensation for the rearfoot varus deformity" as advocated and taught by Dr. Root and his colleagues, is rather designed to reduce the pathological forces causing either the posterior tibial or peroneal tendinitis/tendinopathy, namely excessive subtalar joint (STJ) pronation moments in the former patient and excessive STJ supination moments in the latter patient.

Yes, both the Root orthosis prescription protocol and tissue stress theory use different types of biomechanical concepts to explain how foot orthosis should be designed and how they work. However, judging by the lecture content presented at the 35 international podiatric biomechanics seminars that I have been invited to lecture at over the past 24 years, the Root orthosis prescription protocol is becoming more rarely discussed while tissue stress theory is becoming increasingly more discussed. In fact, at the upcoming Biomechanics Summer School in Manchester, UK that I will be lecturing at next month on June 19-20, 2015, the whole seminar is devoted to tissue stress theory, with the seminar title being The Tissue Stress Theory and Its Clinical Relevance.

http://biorthotics.com.au/biomechanics-summer-school/Summer_School_2015_...

Certainly, Dr. Root's name and his accomplishments will be mentioned for their historical significance during some of the lectures at this seminar, as it rightly should.  However, the international podiatric biomechanics community is increasingly realizing that tissue stress theory is the future for our profession as a more effective orthosis prescription protocol for our patients and which also is a more theoretically coherent theory of foot orthosis prescription that uses the modern physics and engineering concepts of the International Biomechanics Community.

Kevin A. Kirby, DPM

Adjunct Associate Professor, Department of Applied Biomechanics, California School of Podiatric Medicine

Private Practice, Sacramento, California

Aloha,

Theories are only theories until they are proven fact.

To claim that "the tissue stress theory is currently the best method by which to design prescription foot orthoses" without significant evidence seems hopeful.

Very little evidence has been brought forward in this article to prove that the "Tissue Stress Theory" is more effective than the "No Dah Theory".

Claiming to reduce the tension or compression of certain body parts/tissues is great but how do you measure it? Where is the evidence that adding a 1/8 inch soft top cover will help reduce ground reactive forces (GFRs) more than the hunk of wedged foam it is sitting on? And will that 1/8 of extra top cover be enough to mitigate the very large impacts our very large patients produce? Are they placing probes in the tendons and fascia of walking people and measuring the effectiveness of their prescriptions vs Root-based or other newer gait systems?

If we really want to develop a new system for orthotic prescriptions, perhaps we should look closer at how we make orthotics and the shoes (midsoles and soles) that support them. Are we just rehashing the same plastic orthotic-insert on the same bed of deforming foam with a new slick pitch? More solid science is needed before making the big claims of uber superiority.

Mahalo,
Steve

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