A compromise exercise in insoles

Diabetic feet require support and stability, as well as protection from microtrauma. The diabetic insole is the perfect compromise between shoe and sock. It should provide the best of both worlds: structure, shock absorption and cushioning.

Rothenberg, an attending podiatrist who is also the director of residency training at Miami VA Healthcare System, stated that insoles are more important than shoes. “The insole is the point of contact between the foot, the rest of the body, and the outside world. I am usually comfortable with an off-the shelf shoe that can accommodate the insole I have prescribed.

It is obvious that most patients would prefer a contact point that is as comfortable and soft as possible. For diabetics and neuropathy patients, however, an insole must offer all the benefits: structure, shock absorption and cushioning diabetic custom foot orthotics

Materials and configuration

Roy H. Lidtke, DPM, CPed and FACFAOM, an associate professor of podiatric surgery at Des Moines University, Iowa, and director of St. Luke’s Hospital’s Center for Clinical Biomechanics in Cedar Rapids (IA), explains that insole materials should have similar properties to human skin for optimal compression and density.

“A plastazote that has a Shore A20 compression factor is very similar to skin. The soft material will compress very quickly. Multidensity layering is what you need to make sure the insole lasts longer.

Combining a range of materials with different functions to get the best of both worlds is what we call the “best of both”. (see table).

Bill Meanwell, CPed founder, CEO and director of Broken Arrow’s International School of Pedorthics, OK, believes that all insoles worth their salt will contain at least three materials.

1. Top cover for Plastazote Pcell

Plastazote, and P-cell are self pressure mapping products that are intended to alleviate pressure points during normal wear. Because areas with high peak plantar pressures are more susceptible to ulceration, it is important to have even distribution of pressures in diabetic feet. Pressure gradients (steep pressure increases over a small area) can increase friction and lead to calluses and ulcers. These topcover materials are resistant to bacteria. Patients with diabetes are more susceptible to infection than those in healthy people. This can make it difficult to get an ulcer or worsen cellulitis.

2. Polyurethane foam

A layer of polyurethane provides incredible shock absorption. This can reduce peak pressure in the areas mentioned and compensate for limited motion, especially ankle dorsiflexion, which is common among diabetic patients. This limited motion can affect a diabetic patient’s ability to seamlessly transition between the phases of gait. It also reduces the ability to absorb shock at impact points. The foot is protected from unnecessary stress by the polyurethane foam, which absorbs shock.

3. EVA (ethylene vinyl acetate)

Rothenberg stated that a bottom layer of 35–45 durometer would provide some “guts” for the entire thing. Sole stability reduces plantar pressures, shear forces and protects the foot from lesions like calluses or ulcers. Stability can also improve postural control. This is especially important for patients with diabetes or neuropathy. Patients at risk of falling due to poor postural control.

The insole development process of Rothenberg begins with a thorough exam. This includes a neurological exam, dermatological exam and a neurovascular exam.

He said that the musculoskeletal section of the exam is crucial for choosing which type of insoles to use. So if the patient has a callus, a healed ulcer due to a hammertoe, or a plantar-flexed metatarsal we might choose to pocket the insert or offload it based on the history. Deformity is the main determinant of which type of insole I choose.

Off the shelf vs. Custom

Orthotic devices will be required for patients with foot deformities or significant changes in foot architecture, caused by motor neuropathic changes, autonomic, or motor neuropathic. Experts say that this is only a small percentage of diabetic patients.

Meanwell stated that “The A5513 is necessary occasionally”, referring to the Healthcare Common Procedure Coding System, (HCPCS), used to get Medicare reimbursement for custom-made insoles. The problem in our industry is that custom devices are often more expensive than OTS (off-the-shelf). Your wallet is your only guide, not your head.

Marybeth Crane MS, DPM. FACFAS, CWS is the managing partner at Foot and Ankle Associates in North Texas in Grapevine. She also stresses that a heat moldable OTS can be used for most patients. She stated that a properly fitting shoe should have a moldable sole.

She stated that there are strict guidelines that insoles must meet to be reimbursed. They must be comfortable, soft and fit the patient’s feet. An OTS device can quickly make minor adjustments such as adding a metatarsal pad or a heel lift.

These accommodations can be used to address many issues related to diabetic feet, including excessive plantar pressure and forefoot valgus. The ultimate goal of these accommodations is to reduce foot loading, relieve pain, and minimize the risk of soft tissue injury.

Rothenberg said that custom shoes are rarely needed for patients with Charcot arthropathy and partial foot amputations. Rothenberg said that he can often get these patients into OTS shoes paired with a heat-moldable OTS insole.

He said that if they brought in a decent shoe they bought at WalMart or Kmart, I could at least get them an insole.

Neuropathy

Because elevated plantar pressure can lead to foot ulcers in the neurotic foot, insoles are frequently prescribed. According to a systematic review by the University of Plymouth, the UK, published in the 2011 Journal of Diabetes & Its Complications, there is not much data available on insoles’ effectiveness in preventing ulceration.

Joanne Paton, PhD, is a lecturer at the university, and her colleagues culled 342 papers about the topic. They then narrowed it down to five papers that met their inclusion criteria. See Table 2. The studies could have been randomised or controlled in a non-randomized manner. Two studies examined plastazote-based cast insoles. One assessed ulcer relapse rates (Ucciloi), while the other measured peak pressure (Mohamed). One study examined the impact of EVA and polyethylene foam on peak pressure (Lobmann), while another looked at the effectiveness of magnetic insoles for reducing neuropathic discomfort (Weintraub). Albert’s last study examined the impact of a TL-2100 graphite-casted insole on peak and contact pressure (Albert).

Based on all five studies, Paton’s team concluded that insoles were effective in preventing neuropathic diabetes foot ulcers by reducing the peak pressure below the first metatarsal head area by 20–30%. As other researchers have pointed out, it is easier to find evidence from diabetic foot care literature that shows plantar pressure reduction using footwear and insoles, than it is to prove that these effects actually reduce ulceration rates. Only one University of Plymouth study, Uccioli, used ulcer relapse to conclude its review. The rate of relapse in patients who had an insole and a therapeutic shoe was 27.7%, compared to the rate in the control group (those who had non-therapeutic shoes but had insoles) which was 58.3%.

Paton’s team also pointed out that only four of the studies had poor methodology (Weintraub being the exception). These weaknesses included insufficient generalizability, bias potential due to patients not being blinded to the interventions, and poor randomization. They urged the diabetes healthcare community to conduct more thorough studies.

She stated that insoles may be effective in reducing plantar pressure under diabetic neuropathy foot. Insoles can be beneficial in areas where the goal is to reduce pressure on the plantar area. However, it isn’t clear if they are effective in reducing the rate of ulceration. We don’t recommend that insoles should be used as an isolated treatment but as part of a comprehensive strategy to prevent future ulcerations.

This recommendation is supported by a study from the Netherlands. A 2004 paper published in Clinical Biomechanics by researchers at the University of Amsterdam found that custom-made, rather than flat, insoles performed better in offloading the first metatarsal head area. However, this offloading was different for each patient.

Insole education

Paton’s study found that insoles need to be replaced and reviewed regularly. LER spoke to experts who recommended that insoles should be replaced at least three times per year. This is the maximum number allowed under Medicare’s Therapeutic Shoe Bill. Some patients might prefer to purchase all three pairs at once, and then switch them out regularly. Some prefer to have one pair.

Ribotsky keeps the expiration date on his insole to remind him of the thrice-yearly exchanges he has with his patients who are eligible under the TSB program.

He said, “I also send out automated e-mails reminding people to change their insoles.”

Rothenberg is the chair of the foot specialty practice group of the American Association of Diabetes Educators. He said that his group sees high-risk patients quarterly, which gives them the opportunity to change their insoles. Rothenberg said that some patients prefer to purchase all three pairs of insoles upfront, so they can rotate them throughout each year.

According to another study by Paton’s University of Plymouth group, patients with diabetes that are not covered under the TSB may be able go longer between insoles replacements without significantly affecting their plantar pressure attenuation. The insole durability study was presented at the International Foot & Ankle Biomechanics conference in September. It found that while insoles compress during the first six months, peak plantar pressures do not change for six additional months.

Insole materials

Construction using open-cell technology

• Latex and polyurethane foam
• Microcellular rubber
• Polyvinyl chloride (PVC)

Construction in closed cells

• Polyethylene foam (plastazote)
• Neoprene

Ethylene vinyl acetate (EVA)

• Ortho felt
• Leather
• Charcoal
• Bamboo