Skip to main content
Letters

Emphasizing An Awareness Of Study Methodology When Assessing Results From Studies On Orthotics

I would like to commend Doug Richie Jr., DPM, FACFAS, for an excellent review of the literature in regard to whether orthotics are effective in alle­viating the pain of plantar fasciitis (see “Orthoses For Plantar Fasciitis: What The Evidence Reveals” in the November 2015 issue).

The author brought out quite well that the argument of custom versus prefab­ricated orthoses continues with various results. It is true that every clinician is looking for literature to support his or her own opinion and practice algorithms, and there is literature that can support every opinion that exists. Therefore, I believe that in the future, reviewers of the litera­ture need to pay much more detail to the methodologies utilized that produced the successes or failures of orthotics. I will use three examples from the references listed by Dr. Richie to show the importance of paying attention to detail and not mak­ing leaps of faith in trying to interpret the results.

An excellent research paper by Kogler and colleagues looked at how much vari­ous types of orthotics alleviated the ten­sion in the plantar fascia.1 Using a cadaver foot and leg, the authors assessed orthotics made with various materials and various casting techniques. Researchers placed the orthotic on the foot and placed a verti­cal load on the tibia, measuring the ten­sion in the plantar fascia by a strain gauge embedded in the plantar fascia. The result was that the Root type of orthotic made from a non-weightbearing cast was to­tally ineffective in alleviating the tension whereas three other non-Root orthotics made from semi-weightbearing casts were effective in decreasing tension.

The first reaction to this research would be to advocate that clinicians should reject the Root technique in favor of the semi-weightbearing techniques when treating plantar fasciitis.1 However, a closer look at the methodology shows that there may be other factors at play.

First, the Root orthotic in this study was made from TL-61® carbon fiber/ acrylic laminate.1 The study does not note the thickness of the material. I had very early experience with this material when it was introduced. I found out that it is anisotropic so while it feels rigid to the touch and even resists bending in the direction that the fibers are oriented, it is much less resistant to torsion. Due to this lower resistance to torsion, the forefoot can invert against the rearfoot easier than with a homogenous acrylic and the me­dial band of the plantar fascia may have increased tension. The study would have been much more valid if the researchers had used a isotropic material with better resitance to torsion. If one looks at two of the orthotics that did alleviate tension, the “semi-rigid” orthotics were very thick under the medial arch, which could give them more rigidity than the Root device. Many researchers confuse the reader with durometer properties but the durometer is only a reading of the softness of the top 1/8-inch and does not really reflect how well the orthotic bends or resists bending when one stands on it. ­

Besides the two “soft” orthotics that were effective, the other orthotic that re­sisted tension was the University of Cali­fornia Biomechanics Laboratory (UCBL) device, which was made from an un­known “rigid” material.1 This orthotic has much greater complexity of curvature so it would provide much greater resis­tance to bending than the “Root” device. Unfortunately, the authors provided us absolutely no information on how much the various orthotics deflected from their original shape when they were loaded with the force of the foot pushing down on them.

So did the authors prove that the Root orthotic was inferior to the non-Root custom device? Certainly, their “Root” device was inferior in the study but this does not mean that all “Root” devices are inferior. We have no idea how much the arch on the positive Root cast was filled with plaster. Certainly, the effective or­thotics had no filler so they hugged the medial arch of the original cast very tight­ly but the Root device did not.

Second, we have no idea what the dif­ference was in the cast shape between the semi-weightbearing and the non-weightbearing casts.1 We have no idea how a cast of a cadaver foot compares with the cast of an in-vivo foot. If there is little motion in the midfoot joints, then we would expect only minor differences in a semi-weightbearing cast and a non-weightbearing cast. This would mean that a semi-weightbearing cast with a tight fit to the medial edge of the foot and stiff­ness due to thickness may be more effec­tive than the “Root” device.

Raising Questions Over Definitions Of ‘Semi-Rigid’ And ‘Sham’ Orthotics

In the second example, let us consider the study by Landorf and colleagues, for whom I have only the greatest respect.2 However, the methodology section states:

“The sham foot orthosis was fabri­cated by molding 6-mm, soft (120 kg/ m3) ethyl vinyl acetate foam over an un­modified cast of the foot. This device was designed to provide minimal structural support for the foot. .... The customized foot orthosis was fabricated at a com­mercial orthotic laboratory [I withheld the name] using principles described by Hice. A plaster cast was posted to the neutral calcaneal stance position, and a hard plas­tic shell was vacuum molded over the cast. The shell was made from semirigid polypropylene, and a firm foam heel post was applied inferior to the heel. This de­vice is relatively rigid and is designed to provide significant support for the foot and influence the position of the foot relative to the leg.”2

In this study, the final outcome was that the prefabricated and custom orthotic had about the same positive effect in the short run. However, in the long run, they both were no more effective than the sham or­thotics.2 This would make one immedi­ately conclude that it would be a waste of money to use customized orthotics because prefabricated orthotics would be just as effective. I do not object to using prefabricated orthoses as an initial therapy as they do work many times. However, there are some problems with this meth­odology that could lead to the erroneous conclusion that custom-made orthotics are never indicated.

Let us look a little bit closer at the methodology in this study. The research­ers gave us no idea what thickness of polypropylene was used or their defini­tion of “semi-rigid.”2 Since the stiffness of the orthotic is proportional to the cube of the thickness of the material, we know that a 3/16-inch polypropylene is 3.4 times stiffer than 1/8-inch polypropylene and 1/4-inch polypropylene is 2.4 times stiffer than 3/16-inch polypropyelene. So what constitutes semi-rigid? Without any indication of thickness, we have no idea as to the stiffness of the orthotic in the study. We also had no idea what the dif­ferences in the curvature of the prefab­ricated orthotics were from the custom-made orthotics. If the shapes were very close, wouldn’t it be logical that the results would be about the same?

Note that researchers made the “sham” orthotic over the same mold as the cus­tom-made, semi-rigid orthotic. Is this really a sham orthotic? Does such an or­thotic have zero supportive effect? Also at one year, what were the changes in the shape and flexibility properties of the pre­fabricated orthotics? Did they support the foot to the same degree at 12 months as they did at the beginning of the proj­ect? How do we know that there were no changes in the shape of the foot after wearing the orthotics?

A Closer Look At A Recent Study Comparing Custom And Prefabricated Orthoses

The study by Wrobel and colleagues listed by Dr. Richie serves as a much better ex­ample of comparing custom and prefabri­cated orthotics.3 In this particular case, the authors concluded that the custom-made orthotics were superior to the prefabri­cated orthotics and the “sham” orthotics. The methodology section states:

“A senior experienced biomechan­ics instructor with more than 20 years of teaching and practice experience per­formed all of the biomechanical exami­nations, neutral suspension castings, and CFO prescriptions. All of the patients in the CFO group received a standard pre­scription for functional CFOs posted with the forefoot balanced to the rearfoot de­formity (neutral calcaneal stance position) with the following exceptions: 1) valgus rearfoot (neutral calcaneal stance position) received a flat rearfoot post and 2) rearfoot varus of greater than 6° ­was posted to a maximum of 6° varus. Medium arch fill was used for patients who could not dorsiflex past 0° and for those who were obese (0.30% over ideal body weight); minimum arch fill was used for all of the other patients. Additional accommodations to the prescription process were made depending on body stature, foot type, first ray function, and ankle func­tion … The sham device consisted of a full foot–length, Shore A, 35-durometer, 3-mm thick base layer of ethyl vinyl ace­tate, covered by the standard neoprene top cover. The sham devices were heated for 2 min in a convection oven at 177°­C and then were vacuum pressed onto a positive mold of the respective patients’ feet. Thus, the sham devices had the shaped appearance of a customized device but lacked the structural integrity and support of an actual orthotic device. All sham ortho­ses were fabricated by the same certified ­pedorthist.”3

There are several points of care that researchers took in this study.3 The per­son who took the cast actually did an examination and wrote a prescription that was specific for each individual. Also, the medial arch of most of the orthotics was closer to the contour of the original cast than in the study per­formed Kogler and colleagues.1 Note that the sham orthotic built by this team was half as thick as the sham orthotic built by Landorf and colleagues.2 This means that the Landorf sham orthotic was eight times stiffer than the Wrobel sham orthotic, which again lends cre­dence to the idea that the Landorf sham orthotic may not have been a totally sham orthotic.

Unfortunately, there is still some valu­able information missing in the method­ology section of this article. For example, we have no information about what ma­terial or what thickness of material the study researchers used for the custom or­thotic. Also we know nothing about how closely the prefabricated orthotic shape matched the shape of the neutral foot cast foot shape.

Final Notes

In summary, I trust that the podiatry community appreciates that there are wide variations in the custom-made or­thotic industry. Some practitioners and researchers take great care in their exam­ination and prescription process whereas others treat the custom-made orthotic prescription process with little more care than using it as an expensive prefabri­cated device.

There is certainly much more that we need to learn about the specific details of an orthotic that lead to success or failure to alleviate heel pain, whether the device is custom-molded or is a prefabricated device. I have had many years of clinical success in using custom-made devices yet I recognize that many times, prefabricated devices can be very effective for some people. Much more research remains to be done in regard to the pathomechan­ics of plantar fasciitis and the properties of the orthotics necessary to truly alleviate the pain.  

— Robert D. Phillips, DPM

Orlando Veterans Administration Medical Center, Orlando, Fla.

Professor of Podiatric Medicine, College of Medicine, University of Central Florida

References

  1. Kogler GF, Solomonidis SE, Paul JP. Biome­chanics of longitudinal arch support mecha­nisms in foot orthoses and their effect on plantar aponeurosis strain. Clin Biomech. 1996; 11(5):243-252:
  2. Landorf KB, Keenan AM, Herbert RD. Ef­fectiveness of foot orthoses to treat plantar fasciitis: a randomized trial. Arch Intern Med. 2006; 166(12):1305–1310.
  3. Wrobel JS, Fleischer AE, Crews RT, Jarrett B, Najafi B. A randomized controlled trial of custom foot orthoses for the treatment of plantar heel pain. J Am Podiatr Med Assoc. 2015; 105(4):281-94.

Dr. Richie Responds

I appreciate the comments from Dr. Phil­lips, who is an esteemed colleague and noted contributor to our knowledge of podiatric biomechanics and foot orthotic therapy.

He makes a valid point about the lack of consistency in the description of the method of fabrication or the material composition of the custom foot orthoses tested for their efficacy in treating plan­tar heel pain. We have to assume that the foot will respond differently to various physical properties of foot orthoses and this should have an effect on loading of the plantar fascia during standing and walking.

On the other hand, one has to be im­pressed with the consistency of the results of many studies comparing custom versus prefabricated orthoses in the treatment of plantar heel pain.1-3 Despite a wide range of orthotic materials and design, the find­ings almost always show no difference in the superiority of custom devices in com­parison to prefabricated devices. I know this is likely contrary to the personal clini­cal experience of Dr. Phillips. It certainly is contrary to my own.

For the reasons discussed in the con­clusion of my article, we must continue to learn which patients will benefit from custom foot orthotic therapy and which patients will best respond to prefabricated devices.

— Doug Richie Jr., DPM, FACFAS

Adjunct Associate Professor, Department of Applied Biomechanics, California School of Podiatric Medicine at Samuel Merritt Univer­sity, Oakland, Calif.

Private practice, Seal Beach, Calif.

Letters
10
14
Back to Top