Are Root Biomechanics Dying?

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Author(s): 
Kevin A. Kirby, DPM

   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

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Anonymoussays: February 2, 2010 at 5:24 pm

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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