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Cushioning to Reduce Ulcers

Cushioning to Reduce Ulceration Risk in Diabetic Patients

Cushioning is a critical component of orthotic therapy when prescribing orthoses for patients with diabetes.

In most people, the heel and forefoot fat pads provide adequate cushioning to reduce pressure by compressing and splaying to redistribute force. In the presence of diabetes, the fat pad under the heel and forefoot can become thinner and less effective in reducing pressure. Effects of diabetes on the fat pad include:

  1. Atrophy of the fat pad due to peripheral vascular disease.
  2. Glycosylation in poorly controlled diabetics can lead to decreased integrity of the fat pad.15,16
  3. Anterior displacement of the forefoot fat pad secondary to digital contraction.17 

 Abouaesha and colleagues looked at the relationship between the thickness of the fat pads and plantar foot pressure and found a strong inverse relationship between thickness of the plantar fat pad and pressure under the metatarsal heads in diabetic patients.18 

Cushioning Materials

Given the propensity for decreased natural cushioning in diabetics and the strong relationship between decreased fat pad and increased pressure, it is beneficial to include soft tissue supplements in the form of cushioning materials when prescribing orthoses for diabetic patients. These soft tissue supplements should be included as part of a topcover on an orthotic device. There are many materials available including foams, rubbers and viscoelastic materials. Although there is limited data indicating which of the cushioning materials are the best replacement for the natural cushioning provided by the fat pads, there is some evidence to help us determine the materials that are likely to be most effective.

Paton et al. investigated the physical properties of materials used to fabricate orthoses designed for the prevention of neuropathic diabetic foot ulcers. They found that the most clinically desirable dampening materials was Poron19  Campbell et al. found Poron to have a significantly longer effective life when compared to other soft tissue supplement materials such as soft Plastazote® and Sorbathane®.20  Tong and Ng investigated the amount of pressure reduction for different padding and insole materials. They found significant reduction in minimum and mean pressure with a combination of Poron and firm Plastazote when compared to barefoot and better pressure reduction when compared to Slow Recovery Poron® or Poron plus soft Plastazote.21    

Orthotic Prescription Recommendation:

  • Topcover: A topcover with a soft tissue supplement should be included on all orthoses for diabetic patients. Although the study by Tong and Ng showed the greatest reduction in plantar pressure with the use of Poron and firm Plastazote, firm Plastazote is a difficult material to conform to an orthosis when producing a topcover and insufficient for functional control as an orthotic shell. Poron has a tendency to tear in response to shear forces unless it is covered by a material that is not prone to tearing. The current topcover recommendation is for 3mm or 4.5mm Poron glued to a top layer of leather or 1.5mm soft EVA, either of which will prevent tearing of the Poron.
  •  Forefoot Extension: For patients with significant forefoot fat pad atrophy it is also recommended to prescribe a forefoot extension consisting of another 1.5mm – 3mm thick  Poron. This extension should extend from the distal edge of the orthosis to the sulcus, since a full length extension (to the toes) causes crowding in the toebox of the shoe. Finally, we recommend that the cover be glued only on the posterior half of the orthosis. This allows addition or modification of metatarsal pads and other forefoot accommodations.
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