Key Prescription Pearls For Diabetic Orthotics

Author(s): 
By Eric M. Feit, DPM, FACFAS and Alona Kashanian, DPM

Why do orthotics work in the diabetic population? Several studies have demonstrated that they decrease plantar pressures, reduce shear forces and shock, redistribute force and limit abnormal pronation. In a study by Albert and Rinoie, they determined that you could reduce the plantar pressure under the first metatarsal head and medial heel by 30 to 40 percent with a custom made orthotic. Using an F-scan system, researchers also found the total contact area of the foot had increased, thus redistributing force.2
What Type Of Foot Are You Treating?
Prescribing a diabetic foot orthotic also depends on the type of foot you are treating. We prefer to categorize diabetic feet into two general categories: The rigid foot type and the flexible foot type. As with all orthotic prescription writing, you need to consider the diabetic patient’s weight, which influences the durability and longevity of the device.
The rigid diabetic foot type would include patients who are s/p Charcot neuroarthopathy and pes cavus deformities. Ideally, you want to use softer orthotic materials for these patients. It is our preference to use an EVA shell or 1/4-inch Pelite with a Nickleplast forefoot extension. The EVA comes in different densities. We prefer to use a medium density material. The nickleplast is more durable than the traditional pink plastazote or ppt. We then utilize a leather top cover, which conforms to the foot well, and an aperture/release at the ulcer site.
The rigid foot type prescription should also include a wide width, deep heel cup and minimum cast fill. If the patient has pre-ulcerative lesions or healed ulcers in the midfoot area, you can incorporate an intrinsic “sweet spot” into the orthotic shell. This will allow for off weightbearing of any osseous prominence. You can fill this intrinsic “sweet spot” with poron (ptt) to allow additional cushioning for the healed ulcer.
The flexible diabetic foot type would include patients who have abnormal pronation and a flexible flatfoot. Ideally, you want to use firmer materials with more support. We often prefer a black plastazote shell or a flexible polypropylene. We recommend using a nickleplast forefoot extension, leather top cover and aperture/release at the site of the ulceration.
For the flexible foot type, your orthotic prescription should include a normal width, deep heel cup, minimum cast fill and an aperture for any forefoot lesion.
We recommend using more of a “slot” accommodation of the lesion rather than the “punch” out accommodation. It appears the slot accommodation allows for more effective re-distribution of pressure. When forefoot accommodation is required, nickelplast and medium density EVA appear to be most effective.
Emphasizing Control Of The Diabetic Foot
In recent years, the biomechanical podiatric community has become more aggressive in controlling the diabetic foot rather than simply supporting and accommodating lesions. For the diabetic flexible flatfoot, you should consider using the medial skive technique as well as a small amount of inversion to minimize medial pressure secondary to excessive pronation of the subtalar joint. To control this flexible flatfoot, you need to cast the diabetic patient in the traditional non-weightbearing neutral suspension cast or a semi-weightbearing cast.
The materials we choose for the diabetic patient will often help prevent new ulcerations and recurrent ulcerations. Durability is an important factor in prevention. Orthotics should be checked every three months for signs of deterioration. Once an orthotic has thinned out, it will no longer provide the original pressure reduction. It is common that diabetic patients will go through three to four pairs of orthotics in a year, particularly those who have the rigid foot type.
Shoes are an important aspect of prescription writing for any patient. When dealing with the diabetic patient, it becomes crucial to control the flexible foot as well as support the rigid foot type. Initially, you should consider the ready-made extra-depth shoes, such as Rockport’s Prowalker, SAS’s Freetime or Timeout.

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