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Myth-Busting Concepts About Custom Foot Orthoses

The use of custom foot orthoses to treat foot maladies dates back to as early as 1845 when Queen Victoria’s chiropodist, Lewis Durlacher, developed a molded-leather device to correct for “plantar pressure lesions” and “foot imbalances.”1 During the 175 years since then, the plethora of new types of foot orthoses led to many new ideas about what custom foot orthoses do and what they don’t do. As a result, podiatrists, non-podiatric clinicians and the general public have certain perceptions about custom orthoses that have no basis in fact. With this in mind, let us take a closer look at some common myths about custom foot orthoses. 

First of all, custom foot orthoses do not function by “holding the subtalar joint in neutral position,” “locking the midtarsal joint” or “preventing compensation for rearfoot and forefoot deformities” as I was taught in podiatry school back in the early 1980s. Rather, custom foot orthoses are custom fitted, in-shoe medical devices designed to alter the magnitudes, plantar locations and temporal patterns of the reaction forces acting on the plantar aspect of the foot.2 They do this in order to optimize foot and lower extremity function and decrease specific pathologic loading forces on the structural components of the foot and lower extremity during weightbearing activities.2 

In other words, custom orthoses do not necessarily reposition the foot into different joint positions nor somehow make the foot and lower extremity function perfectly. Rather, custom foot orthoses work with their characteristic three-dimensional morphology, stiffness and cushioning properties to alter the timing patterns, specific locations and magnitudes of ground reaction forces acting on the patient’s plantar foot. Nothing more, nothing less. 

For example, one may design custom foot orthoses to reduce pathologic plantar pressures that may occur in cases involving diabetic neuropathic plantar ulcers and painful plantar calluses. Custom foot orthoses may also reduce the stress on internal tissues of the foot and lower extremity. They may reduce tension stress within the plantar fascia in plantar fasciitis or reduce tension stress within the posterior tibial tendon in posterior tibial tendinitis/dysfunction. 

In addition, by redirecting ground reaction forces to specific areas of the plantar foot, custom foot orthoses may reduce pathological bending moments acting on the long bones of the foot and lower extremity that cause metatarsal stress fractures and medial tibial stress syndrome. These clinical examples are just a few of the pathologies that one can effectively treat with specially modified custom foot orthoses using the concepts of tissue stress theory.3 

Another common myth passed among generations of podiatrists is the idea that there is only one best way to make custom foot orthoses to treat specific pathologies. Considering the nearly infinite permutations in custom foot orthosis design, the limitless possibilities increase the chance of therapeutic success versus pre-made foot orthoses in the trained hands of the skilled podiatric clinician.4 

The most annoying myth about custom foot orthoses is the curious notion, begun by the barefoot running zealots about a decade ago, that custom foot orthoses and even shoes will weaken feet over time. To date, there is no research evidence that supports these odd ideas. In fact, in a recent study using fine-wire electrodes to assess the plantar intrinsic muscles, Kelly and colleagues found that running in shoes resulted in increased activation of the intrinsic foot muscles versus running barefoot.5 Certainly, if foot orthoses somehow weakened feet, patients wearing custom foot orthoses for years, or even decades, would become crippled, rather than electing in many instances to “not leave home without them.” 

It behooves the informed podiatrist to be aware that many persistent myths regarding custom foot orthoses will only vanish when a critical mass of podiatrists become sufficiently educated about custom foot orthosis therapy. Even though I have only touched on a few of the myths about custom foot orthoses, hopefully this refresher will stimulate more interest in this underutilized therapeutic modality for the podiatric specialist.  

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. 

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By Kevin A. Kirby, DPM
References

1. Durlacher L. A Concise Treatise on Corns, Bunions, and the Disorders of Nails with Advice for the General Management of the Feet. London: Simpkin, Marshall and Co.;1845. 

2. Kirby KA. Foot and Lower Extremity Biomechanics II. Precision Intricast Newsletters,1997-2002. Payson, Ariz.: Precision Intricast, Inc.; 2002:8. 

3. 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. Denver: Bipedmed, LLC; 2013:205-264. 

4. Kirby KA, Spooner SK, Scherer PR, Schuberth JM. Foot orthoses. Foot Ankle Spec. 2012;5(5):334-343. 

5. Kelly LA, Lichtwark GA, Farris DJ, Cresswell A. Shoes alter the spring-like function of the human foot during running. J R Soc Interface. 2016;13(119):20160174. 

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