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Nov 29

Written by: Larry Huppin, DPM
11/29/2012 1:02 PM

I just saw a prescription come into ProLab from a new client. The doctor noted on the prescription form that the patient had plantar fasciitis and weighed 280 pounds. Her prescription was for a Featherweight orthosis (a functional orthosis made from medium density EVA). She also ordered a standard cast fill and a standard width.

This prescription had me concerned for several reasons. First, with the patient weighing 280 pounds, this orthosis was not likely to provide much support. This is a fairly flexible device and it will collapse rather quickly under the weight of this patient. Given that, the device would not last very long.

In addition, the prescription was for a standard cast fill. A standard fill is not going to conform close enough to the arch to provide a significant decrease in tension on the plantar fascia. Studies on how orthotics decrease tension on the plantar fascia indicate that those devices that conformed close to the arch do a much better job in decreasing plantar fascial tension.1 You can read a summary of the study by Kogler and colleagues here.

Finally, this doctor prescribed the device with standard width. This would result in a device that is slightly narrower than the foot. When a patient weighs this much, there is so much force on the orthosis that they are unlikely to be comfortable in anything but a full-width orthotic.

I called the doctor and we discussed my concerns. She was worried because the patient previously had a pair of polypropylene orthoses that were uncomfortable. I explained that it was not the polypropylene that made him uncomfortable, but it was much more likely the prescription of the orthotic. Although I have not seen them, my guess is that the orthotics were simply too narrow for the patient’s foot. So the patient was feeling the medial edge of the orthosis. This is a common problem we see in obese patients.

I highly recommend that podiatrists use only full-width orthotics for patients who are overweight. They should explain to these patient that their weight makes it almost impossible for them to get adequate support without a full-width device. However, once their feet feel better and they can exercise, they can hopefully lose weight and once that has occurred, they may be able to get a somewhat narrower orthosis.

Reference
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

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