Are Root Biomechanics Dying?

Kevin A. Kirby, DPM

Yes. While Dr. Root made a number of substantial contributions to the profession, this author says emerging research has exposed flaws with the subtalar joint neutral theory and the curriculum at podiatry schools has shifted toward alternate theories of foot function.

   Forty-three years ago, Merton L. Root, DPM, established and became director of the first Department of Orthopedics at the California College of Chiropody. This college later became the California College of Podiatric Medicine and is now the California School of Podiatric Medicine at Samuel Merritt University. The Department of Orthopedics was soon renamed the Department of Biomechanics in order to reflect the relatively new field of foot and lower extremity biomechanics, a scientific discipline that had become of great interest to researchers in the post-World War II era in their efforts to design better and more functional lower extremity prostheses.

   Dr. Root taught and developed many of his concepts within the Department of Biomechanics with his colleagues, including John Weed, DPM, William Orien, DPM, Christopher Smith, DPM and Tom Sgarlato, DPM. These colleagues collaborated with him to help develop new and exciting ideas on foot and lower extremity function, including the publication of four textbooks on podiatric biomechanics.1-4

   Dr. Root was responsible for many important accomplishments. These accomplishments included:

   • establishing the concept of a neutral position for the subtalar joint;
   • developing a classification scheme for many foot and lower extremity deformities;
   • defining eight biophysical criteria for normalcy as a model of ideal foot and lower extremity structure; and
   • creating and developing the modern thermoplastic foot orthosis and its casting and manufacturing techniques.5-7

   In addition, the Department of Biomechanics, which Dr. Root founded, established the Biomechanics Fellowship program at the California College of Podiatric Medicine. Up until 1998, this program provided post-graduate training in podiatric biomechanics and foot orthosis therapy to many nationally and internationally recognized podiatric biomechanics educators.

   I had the great fortune of being able to attend many lectures given by Dr. Root during my years as a student, my Biomechanics Fellowship and early practice years. During these lectures, I was always impressed by the passion that Dr. Root had for the subjects of foot and lower extremity function, and foot orthosis therapy. He was not only a walking repository of valuable information but was a dynamic speaker who greatly inspired me as a young podiatrist.

   During his lectures, Dr. Root would say he did not want podiatrists to take his word as gospel and that he had more respect for those individuals who challenged his ideas than those who agreed with everything he said. Dr. Root encouraged scientific research that he hoped would lead to better treatments of the painful maladies that podiatrists saw on a daily basis in their busy practices. Dr. Root often stated during his lectures that he fully expected that the information in his textbooks would become outdated within a decade of their publication due to the influx of new scientific data that would lead to a different and more complete understanding of foot function.

Noting The Emergence Of Alternative Theories Of Foot Function In The Curriculum

   Today, over 30 years after the publication of Root, Orien and Weed’s most influential textbook, Normal and Abnormal Function of the Foot, there is now sufficient scientific evidence to conclude that many of Dr. Root’s ideas and theories need to be either modified or discarded in order to more accurately reflect recent research findings and newer theories of foot and lower extremity biomechanics.3

   Even though many podiatrists within the United States have little knowledge of this fact, many podiatry schools in other countries such as the United Kingdom, Canada, Australia and Spain have already started to move away from teaching Dr. Root’s subtalar joint neutral position theory. These schools have moved toward teaching alternative theories of foot function such as subtalar joint axis location/rotational equilibrium theory, tissue stress theory, preferred movement pathway theory and sagittal plane facilitation theory.11-19

   At the California School of Podiatric Medicine, Dr. Root’s subtalar neutral theory is now being taught along with other theories of foot function and foot orthosis therapy that broaden, balance and strengthen the overall biomechanics curriculum for the podiatry students.

A Closer Look At The Flaws With Subtalar Joint Neutral Theory

   The gradual move toward developing and teaching other theories of foot function is at least partially due to the many problems with Dr. Root’s subtalar joint neutral theory that have been noted throughout the years.20,21

   First of all, the neutral position itself is a rotational position of the subtalar joint that has never been adequately defined. A precise anatomical definition of the subtalar joint neutral position is necessary for researchers to determine whether Dr. Root’s theories are reliable and accurate. Unfortunately, the definition for subtalar joint neutral position used by Root and co-workers is “that position of the subtalar joint in which the foot is neither pronated or supinated.”3

   This tautological definition of the subtalar joint neutral position, “neither pronated or supinated,” creates great difficulty for scientific study since it lacks a description of the exact anatomical rotational alignment of the calcaneus relative to the talus that could more precisely define the neutral position.

   In addition, many podiatric biomechanics educators, including myself, have commonly found inter-examiner errors of 5 degrees or more in drawing the calcaneal bisection and determining the subtalar neutral position. One must ensure accuracy for both in order to determine the degree of rearfoot varus/valgus deformity, the degree of forefoot varus/valgus deformity, the neutral calcaneal stance position (NCSP) and relaxed calcaneal stance position (RCSP), all of which are important examination findings in Dr. Root’s subtalar joint neutral theory.

   As a result of these inter-examiner errors, it has been my experience in teaching hundreds of podiatrists and podiatry students that not only does the rotational position of the subtalar joint vary widely when one clinician determines a foot’s neutral position compared to another, but the forefoot to rearfoot relationship, NCSP and RCSP also may vary widely from one clinician to another.

   The result of these differences in interpretation between one clinician and another is that different clinicians may make significantly different orthoses for the same patient, even though the clinicians all think that they are precisely following the teachings of the subtalar joint neutral theory advocated by Dr. Root and his colleagues.

   In fact, in a study by Australian podiatric researchers on the variation in neutral position negative casting of a single foot by multiple experienced and inexperienced clinicians, researchers found that the forefoot to rearfoot relationship of the negative casts ranged from a 10-degree forefoot valgus to a 6.5-degree forefoot varus, or a difference of 16.5 degrees in the forefoot to rearfoot deformity determination on the same foot.22

   If large errors such as these commonly exist, then the measurement of such “deformities” becomes practically useless when it comes to communicating parameters of foot and lower structure between clinicians. These errors would also prevent the precise design of custom foot orthoses for patients with mechanically-based pathologies of the foot and lower extremity.

   Many researchers further doubt that the subtalar joint neutral position is indeed the ideal position of function for the subtalar joint as Dr. Root and colleagues have suggested.3 In walking gait studies of young, healthy patients, researchers have shown the subtalar joint is pronated relative to the subtalar joint neutral position throughout most of the stance phase of gait. These authors also noted that the more pronated RCSP was more representative of the average subtalar joint rotational position than the NCSP.23,24

   This experimental data is in direct disagreement with Root and co-workers, who suggested that the normal foot is more supinated throughout stance phase, pronating past the subtalar neutral position in early stance phase and then supinating past the neutral position in the latter half of the midstance phase of walking gait.3

   Much of this disagreement and confusion may come from Dr. Root’s definition of “normal” foot and lower extremity morphology. Root’s definition is more of a structural ideal for the human foot and lower extremity as opposed to being an average morphology that is present in a group of asymptomatic, young healthy patients who other researchers define as being “normal.”2,3,23,24

   Another problem with the subtalar joint neutral theory is that there is no scientific evidence that supports the hypothesis that one may predict gait function or foot and lower extremity pathology via the determination of subtalar joint neutral position, rearfoot deformity, the forefoot to rearfoot relationship, tibial position or by the first ray range of motion, all of which are measurements that Dr. Root advocated.2 In addition, recent research shows that the idea that two separate midtarsal joint axes, the longitudinal and oblique, coexist together simultaneously is an erroneous assumption.13,25-28

   Furthermore, the idea that the midtarsal joint actually “locks” or has a “locking position” is not mechanically consistent with the known spring-like function of the longitudinal arch of the human foot.29-30 Other problems with Root’s biomechanics theories have been discussed and published previously, and they are still being debated within the international podiatric biomechanics community.31

Recognizing The Pioneering Work Of Root And Colleagues With Foot Orthoses

   The theories of Dr. Root and colleagues attempted to correlate structure to function. While these theories have not been supported by the research to date, this does not mean that we should abandon research that does search for a correlation between structure and function in the human foot and lower extremity.

   With more accurate gait analysis techniques being developed every year, it is quite possible that future research may still support some of the hypotheses of the subtalar joint neutral theory. Additionally, just because the subtalar joint neutral theory may need modification or replacement, this certainly does not indicate that prescription orthoses made with the neutral position casting technique, which Dr. Root and colleagues helped create and develop, do not work extremely well in treating a multitude of mechanically-based pathologies of the foot and lower extremities.4

   In fact, recent scientific research has shown that the foot orthoses that are based largely on the pioneering work of Dr. Root and colleagues produce a significant therapeutic effect for patients with foot and ankle osteoarthritis (OA), knee OA, juvenile rheumatoid arthritis, rheumatoid arthritis, hemophilia, patellofemoral syndrome, plantar fasciitis, diabetic neuropathic plantar ulcers and metatarsalgia.33-48 These orthoses also reportedly help prevent metatarsal and femoral stress fractures, and may increase the mental health of individuals.49-51

   Researchers have also shown that foot orthoses have significant positive effects on the kinematics and kinetics of the rearfoot, tibia and knee, and on plantar pressures during both walking and running gait.52-68 In addition, the foot orthoses that Dr. Root helped develop improve balance and change the electromyographic patterns of the lower extremity during weightbearing activities.69-74

Final Notes

   In view of all of these facts and in consideration of my role as a podiatric biomechanics educator for the past quarter century, would I say that Root biomechanics are dying? The answer is a definite yes.

   We know for certain that that many of the hypotheses that Dr. Root and his colleagues proposed over the years have not been supported by research evidence and some of these concepts do not adhere to Newtonian mechanics.

   However, and more importantly, should we have any less regard for the accomplishments of Dr. Root just because, as he so often predicted and expected, that his theories from 30 to 40 years ago are now being found to be inaccurate, and may need modification and replacement? The answer to this question is a definite no.

   Without the trailblazing efforts of individuals such as Dr. Root during our early years as a medical discipline, podiatric medicine would simply not be the respected profession that it is today. We owe a great deal to pioneering individuals such as Dr. Root since, even though many of his ideas are rightfully being replaced by more robust scientific theory, his wealth of important contributions to our profession will continue to live on for generations to come.

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


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Dear Dr. Kirby,
Excellent article. I'm currently working with a different model of foot and ankle function with good success. This article confirms to me that what I've been seeing actually could be valid.
Are you aware of studies comparing foot deformities such as bunions, plantar fasciities, hammer toes, etc in developing countries versus our own? I'd appreciate any help pointing me in the right direction.
Thank you,
Rick Olderman

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