Raising Awareness Of The Challenges With Foot Orthosis Research

In this era of evidence-based medicine, the number of published papers on foot orthoses has been increasing every year so podiatrists now have a body of high-quality studies that clearly show foot orthoses are effective at producing positive therapeutic effects for our patients.¹ However, there are inherent difficulties with attempting to perform high-quality foot orthosis research that every podiatrist should keep in mind.

One of the problems with attempting to study orthoses is that many researchers do not fully comprehend the potential biomechanical differences between prefabricated and custom foot orthoses. For example, many studies that claim to have used “foot orthoses” in their research have utilized prefabricated orthoses instead of the custom foot orthoses that podiatrists widely use. Many researchers may believe that prefabricated foot orthoses are preferable for their research since prefabricated orthoses require no orthosis laboratory fabrication time or expense.

Unfortunately, prefabricated orthoses, using a “one-size fits all” principle, do not account for the complex, three-dimensional geometry of the plantar aspect of each individual foot. As a result, prefabricated orthoses do not provide the close contact and congruity to the plantar foot that are often necessary to optimize the alteration of loading forces on the plantar foot and allow the foot orthosis to be therapeutic and comfortable for the patient on a long-term basis.² Researchers have even used insoles with medial arch pads or other generic types of in-shoe pads in their “foot orthosis research,” which may have decreased the kinetic and kinematic effects that would have been evident if physicians had used custom foot orthoses, which were properly made and adjusted, in their research.

In addition, well-trained podiatrists don’t dispense the same custom orthoses to every patient and then do absolutely no adjustments on their patients’ orthoses in subsequent follow-up visits. In nearly all orthosis research studies, researchers do not modify the original orthoses that they dispense to patients in order to optimize the comfort and therapeutic function of the orthosis. It is likely that this lack of orthosis optimization during follow-up visits in nearly all research studies on foot orthoses significantly decreases the apparent therapeutic benefit of custom foot orthoses perceived by the research and medical communities.

Another aspect of orthosis research that has become increasingly problematic over the past 15 years has been caused by researchers assuming that soft, flexible insoles or orthoses have no significant kinetic or kinematic effect, and thereby are “sham” insoles or orthoses. In a 2006 study on plantar fasciitis, researchers used a 6 mm thick soft ethylene vinyl acetate (EVA) orthosis, molded to a cast of the patient’s foot, as a “sham” foot orthosis.³ Not only did the soft EVA orthosis in this study provide a cushioning effect to the foot, the custom molding of this “sham” orthosis should have prevented the authors from considering this custom-molded orthosis as a “placebo” or “sham” orthosis with no kinetic or kinematic effect.

Other biomechanics researchers have recently questioned what constitutes a “sham” or “placebo” orthosis. In 2015, two researchers from the University of Calgary School of Biomedical Engineering made the point that even a flat, cushioned insole produced kinetic and/or kinematic changes that should have prevented researchers from considering that insole as either a “sham” or “placebo” insole.⁴

Therefore, it is no easy task to design foot orthosis research that is clinically meaningful with a high level of evidence and takes into account the wide variation in orthosis prescribing habits of podiatrists. Can a research patient wear a shoe insole as a “sham” or “placebo” that truly has no kinetic or kinematic effect? Can researchers duplicate the therapeutic effectiveness of custom foot orthoses that podiatrists dispense and modify in their offices, sometimes over multiple visits?

These questions and many more will complicate our understanding of the valuable role that custom foot orthoses have in treating our patients for years to come. It is important that the podiatrists of today become aware of these inherent problems in custom foot orthosis research so they may develop a better understanding of these research issues for the benefit of their patients.

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.     Kirby KA. Evolution of foot orthoses in sports. In: Werd MB, Knight EL, Langer PR (eds): Athletic Footwear and Orthoses in Sports Medicine. Second Edition. Springer, New York, 2017, pp. 19–40.
2.     Kirby KA, Spooner SK, Scherer PR, Schuberth JM. Foot orthoses. Foot Ankle Specialist. 2012; 5(5):334-343.
3.     Landorf KB, Keenan AM, Herbert RD. Effectiveness of foot orthoses to treat plantar fasciitis. A randomized trial. Arch Intern Med. 2016; 166(12):1305-1310.
4.     Lewinson RT, Stefanyshyn DJ. Losing control over control conditions in knee osteoarthritis orthotic research. Contemporary Clin Trials. 2015; 42:258-259.