Emerging Concepts In Orthoses For Patients With Diabetes
Our expert panelists discuss whether reducing shear in patients with diabetes is comparable to reducing plantar pressure, when to change insoles and the optimum insole depth, and the future of computer-aided design for orthoses.
What is the role of “shear” in orthoses for patients with diabetes? Is “shear reduction” the new plantar pressure reduction?
As custom orthotics have evolved, Eric Feit, DPM, notes that DPMs have traditionally emphasized designing diabetic orthoses to reduce plantar pressures. However, he says shear forces may be the most important factor in preventing ulcerations. Shear or frictional forces cause the skin to stretch or bunch up at the plantar aspect of the forefoot, which is most common at the plantar aspect of the first and fifth metatarsals, according to Dr. Feit. In an elderly patient with thin skin or a patient whose skin is thin from a prior ulceration, Dr. Feit says shear forces may create a break in the skin very easily.
James Wrobel, DPM, notes that peak shear and peak pressure are not necessarily the same. Citing a study by Yavuz and colleagues in patients with diabetic peripheral neuropathy (DPN), he says the authors found that peak shear and peak pressure only correlated about 20 percent of the time in patients with DPN and did not correlate at all in control patients.1 Dr. Wrobel adds that Yavuz and colleagues also reported peak shear at the hallux whereas peak pressure occurred underneath the second metatarsal head in the patients with DPN.
From a clinical perspective, Dr. Wrobel believes this makes sense.
“How many times have you seen an initial presentation of an untreated hallux ulcer, which was heavily macerated with subdermal bleeding compared with those ulcers presenting in other regions of the foot?” asks Dr. Wrobel.
Dr. Wrobel also cites studies that did not find a correlation between the location of pain and peak pressure in patients with pes cavus.2,3
Both Dr. Wrobel and Christopher Nester, BSc(Hons), PhD, are cautious about the potential impact of shear reduction.
“For sure, reducing shear is a laudable aim but achieving it is complex,” says Professor Nester.
With too little friction, Professor Nester says there would be a risk of the foot colliding with the sides of the shoes and this could lead to further problems. He also cites the importance of shoe fit in the equation.
“A great deal depends upon the fit of the shoe rather than the insole. A foot can be held very firmly by a shoe, so much so that any insole technology aimed at shear reduction can be negated,” explains Professor Nester.
Dr. Wrobel notes shear and vertical forces are important but different. In the gait lab, he notes the shear components of the ground reactive force represent about 5 to 20 percent of body weight compared to the vertical component representing up to 120 percent of body weight.
Why do we need to change insoles every three months? How do we know when to change them?
All panelists note the importance of careful observation rather than a strict timeline in determining when to change insoles. Dr. Wrobel says the decision to change insoles should be based on individual patients.
“One size simply doesn’t fit all in this case. I think we have to stay ‘old school’ and look and feel for wear patterns,” maintains Dr. Wrobel.
Dr. Feit concurs, saying he will change the insole when the device looks thinner in the forefoot or if the patient’s skin shows any signs of pre-ulceration or increased callus formation since the last office visit.
Although Medicare covers three pairs of orthotics every year for patients with diabetic neuropathy, Dr. Feit notes all orthotics do not wear out that fast. He says the orthotic wear depends on the stability of the foot, the weight of the patient and the activity level of the patient.