Key Prescription Pearls For Diabetic Orthotics

It is typically easier to heal a diabetic foot ulcer than it is to prevent recurrence. Once you’ve healed the ulcer, the next challenge is to minimize pressure at the site of the old ulceration or the site of a boney prominence. If the patient has never had an ulcer but has a high risk for ulceration, then employing pressure off devices is essential for prevention.
Obviously, the large majority of diabetic foot ulcerations are preventable. There are several keys to prevention, which include organized treatment protocols, early detection, aggressive wound care, orthotics and appropriate shoes. For this column, let’s take a closer look at orthotic management and materials.
Initial diabetic patients should be screened for the risk of ulceration. This includes evaluating their circulation (i.e. pedal pulses, subpapillary venous plexus filling time, and ankle brachial indices if the vascular status is questionable) and their protective threshold via a 5.07 Semmes Weinstein monofilament test. In addition, be sure to check for boney prominences or sites of old ulceration.
Based on this exam, you should be able to classify the patient into a foot risk category, which will help you choose an appropriate orthotic (See Table 1 on page 16). The pre-fab orthotic can be purchased OTC or through a lab. The most common materials are Spenco with an EVA shell and ppt in the forefoot extension. Some labs have a trilaminate of plastazote (two different densities) and one layer of ppt.
Using proper orthotics and shoes will save many feet from unneccesary amputation and infection. You can employ these devices for initial treatment, but it is vital to recognize when these devices are inadequate and when there is a need for surgical intervention in the diabetic patient. It is often necessary to perform surgery first and then utilize orthotics and special shoes for long term foot/limb salvage.
The biomechanics of the foot often increase plantar pressures in the diabetic foot, more so than in the rest of the population.1 This is primarily due to peripheral neuropathy which may result in the diabetic patient being unable to feel abnormal pressure points during gait. This leads to increased motion of the affected joints and subsequently increased shear forces. In a patient with abnormal pronation, there are often higher pressures under the first metatarsal head and medial aspect of the heel, which may lead to ulceration.
The Benefits Of Custom Orthotics
There are several goals of using custom-made orthotics for the diabetic patient. When a high risk patient comes in for his or her initial office evaluation, it is vital to recommend a custom device to help prevent ulceration. Orthotics will help improve ambulation by controlling pronation and minimizing stress on the muscles of the foot and leg. The more a diabetic patient can stay active with walking and exercise, there is less chance for the possibility of other diabetic complications such as heart disease, stroke, kidney disease and eye disease. This is a direct result of improved blood glucose control.
You may also use custom orthotics to treat foot ulcers. Although it is ideal to heal the ulcer first, it may not always be the best thing for the patient. Some patients must stay active and continue to walk in shoes, depending upon their job or general health conditions. We typically recommend waiting until an ulcer is less than 1cm before using an orthotic. If you use an orthotic with an open ulcer, you can place it inside a below knee cam walker for maximal benefit. When it’s absolutely necessary, you may place the orthotic in the shoe.
In our experience, once diabetic patients stop walking, their general health and mental health quickly deteriorate. Having a foot ulceration for several months or years has a tremendous effect on their quality of life and morale. Therefore, prior to utilizing an orthotic for an open ulcer, we typically employ a total contact cast or felt to foam dressing with an aperture to offload the ulcer. Once the ulcer is healed or less than 1 cm, then we dispense the orthotic.
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.
If you see a need for further control of forefoot lesions, consider adding an extrinsic metatarsal bar to the ready-made shoe. This addition will allow you to provide easier propulsion and off weightbearing of the forefoot. You can also prescribe a rocker-bottom shoe for the diabetic patient, who appears to have an apropulsive gait. Any good shoemaker in the community is able to incorporate either a metatarsal bar and/or a rocker-bottom addition.
Most prosthetists will dispense pre-fab plastazote type orthotics for extra depth or custom made shoes. These are often in layers of pink and white plastazote with occasional poron or ppt. These devices do not control the foot well and typically wear out in one to two months, depending upon the activity level of the patient.
Final Notes
Emphasize to your patients that the biomechanics of their feet affect their risk for ulceration, and that a custom-made device will provide better protection. Indeed, it is our role to protect the diabetic foot from ulceration, and to explain to our patients that what they can’t feel can hurt them. n
Dr. Feit is a Diplomate of the American Board of Podiatric Surgery and is the Director of Research at the San Pedro Peninsula Hospital Residency Program. He is also in private practice in San Pedro and Torrance, Calif.
Dr. Kashanian is a Diplomate of the American Board of Primary Medicine and Podiatric Orthopaedics, and is a consultant for ProLab Educational Institute. She is also in private practice in Northridge, Calif.
Dr. Steinberg is an Assistant Professor in the Department of Orthopaedics/ Podiatry Service at the University of Texas Health Science Center.

References:

References

1. Boulton, A.J.M., Hardistry, C.A., Betts, R.P., et al. Dynamic Foot Pressure and other studies as Diagnostic and Management aids in Diabetic Neuropathy. Diabetes Care 6:26-33, 1983.

2. Albert, S., Rinouie, C.Effect of Custom Orthotics on Pressure Distribution in the Pronated Diabetic Foot. J. Foot Ankle Surg., 33: 598-604, 1994.