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Diabetic Pressure Control with Orthoses

Using Orthoses to Prevent and Treat Diabetic Foot Ulcers by Decreasing Pressure

Decreasing pressure in areas at risk for ulceration is one of the two critical functions in ulcer prevention. The other is decreasing friction.

Pressure is the amount of force acting per unit area (e.g. pounds per square inch). When prescribing orthoses that are designed to decrease pressure, it is critical to understand that the larger the surface area over which force can be distributed on the plantar foot, the less pressure on any one area of the foot. In addition, pressure that would be considered normal and non-pathologic in the non-diabetic population may lead to ulcers in the diabetic patient.4,5

To most effectively reduce peak pressure on the plantar foot, an orthosis should act to distribute force over the largest possible surface area. The wider the orthosis, the better it will distribute force since it provides a larger surface area. The orthosis should also conform very closely to the arch of the foot. Mueller and colleagues showed a reduction in peak plantar pressure of 16-24% using a total contact insert which acted to increase contact surface area by 27%.6

Rigidity of the device is also critical. Traditionally softer orthoses have been prescribed for patients with diabetes and with a history of ulceration. However, softer orthoses simply deform under body weight and do not distribute pressure as effectively as a more rigid orthoses. 7,8

Orthotic Prescription Recommendation: To distribute pressure over the largest possible surface area, the orthosis should conform close to the arch of the foot, be at least as wide as the foot and rigid enough to resist deformation.

    • Cast: For an orthosis to conform closely to the arch of the foot, use a nonweightbearing neutral suspension cast of the foot with the subtalar joint in neutral postion, the midtarsal joint locked and the 1st ray plantarflexed. Casting in a semiweightbearing position often leads to ground reactive forces causing a flattening of the arch (dorsiflexion of the 1st ray) during casting. The resultant orthosis will have an arch lower than the actual arch height and will not provide full contact with the arch for optimal pressure redistribution. 9,10
    • Cast fill: Prescribe  minimum cast fill. Minimum fill means that less fill is added to the medial arch of the positive cast, resulting in an orthosis that conforms closely to the arch of foot.
    • Width: Prescribe a wide orthosis and/or incorporate a medial flange in order to distribute force over as large of a surface area as is possible.
    • Material: Use an orthotic  shell material that is not prone to excessive deformation under body weight, for example a semirigid polypropylene

Other orthotic modifications that will help decrease pressure include:

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