Insoles: a compromise exercise

 

Diabetic feet need support and stability as well as protection against microtrauma. The diabetic insole offers the best compromise of shoe and socks. It is designed to provide cushioning, shock absorption, and structure.

Rothenberg is an attending podiatrist and also the director for residency training at Miami VA Healthcare System. He stated that insoles are far more important than shoes. The insole is the interface between the foot and the outside world. I'm usually happy with any shoe on the market that can fit the insole I have recommended.

Most patients prefer to have a contact point that's as soft and comfortable as possible. An insole should offer all of the following benefits for diabetics and patients with neuropathy: structure, shock absorption, and cushioning diabetic foot orthotics

Materials and configuration

Roy H. Lidtke (DPM, CPed, and FACFAOM), is an associate professor of podiatric surgical at Des Moines University in Iowa and the director of St. Luke's Hospital's Center for Clinical Biomechanics, Cedar Rapids (IA). He explains that insoles should have the same properties as human skin for optimal compression.

A plastazote with a Shore A20 compressibility factor is very similar in appearance to skin. The soft material will quickly compress. To ensure that your insole lasts longer, you will need multidensity layering.

The "best of both" is a combination of different materials and functions. (see table).

Bill Meanwell, CPed founder and CEO, is the director of Broken Arrow's International School of Pedorthics. He believes insoles that contain at least three materials.

1. Plastazote Pcell top cover

Plastazote and P-cell, self-pressure mapping products, are designed to relieve pressure points during normal wear. High peak pressure areas are more susceptible to bruising, so it is important that diabetic feet have an even pressure distribution. Pressure gradients (high pressure increases in a narrow area) can cause friction, which can lead to calluses or ulcers. These topcover materials are resistant against bacteria. Diabetes patients are more likely to get infected than people who are healthy. This can make it more difficult to get an infection or worsen cellulitis.

2. Polyurethane foam

The layer of polyurethane offers incredible shock absorption. This can lower the peak pressure and compensate for ankle dorsiflexion which is common in diabetic patients. The ability of a diabetic patient to seamlessly change between phases of gait can be affected by this limited motion. It also decreases the ability of the foot to absorb shock at impact points. Polyurethane foam absorbs shock and protects the foot from any unnecessary stress.

3. EVA (ethylene vinyl acetate)

Rothenberg said that a layer of 35-45 durometer on the bottom would give some "guts" to the whole thing. Sole stability helps reduce plantar pressures and shear forces, as well as protecting the foot against lesions such calluses and ulcers. Postural control can be improved by stability. Patients with neuropathy or diabetes will find this especially important. Poor postural control can lead to patients at high risk of falling.

A thorough examination is the first step in Rothenberg's insole development process. This includes a neurovascular exam, dermatological exam, and neurological exam.

The musculoskeletal section is critical for deciding which insoles to use, he said. We might decide to either pocket or toss the insert based on the history. The main determinant of the type of insole that I choose is whether or not there are any deformities.

Off-the-shelf vs. Custom

Patients with foot deformities, significant changes in foot architecture or motor neuropathy, will require orthotic devices. Experts believe that this only represents a small proportion of diabetic custom foot orthotics patients.

Meanwell stated that "The A5513 was necessary occasionally", referring specifically to the Healthcare Common Procedure Coding System (HCPCS) used to receive Medicare reimbursement for custom insoles. Custom devices are more costly than OTS (off the shelf) in our industry. Your wallet is your only guide, and not your head.

Marybeth Crane MS, DPM. FACFAS, CWS manages Foot and Ankle Associates in Grapevine, North Texas. A heat moldable OTS is also available for most patients. A moldable sole is essential for a shoe that fits properly.

Insoles must be in compliance with strict guidelines to be eligible for reimbursement. They should be soft, comfortable and fit the patient's foot. OTS devices can make minor adjustments quickly, such as adding a metatarsal pads or a heel lift.

These accommodations can be used for many problems related to diabetic feet such as excessive plantar pressure or forefoot vagus. These accommodations are designed to reduce foot load, alleviate pain, and minimize the chance of soft tissue injury.

Rothenberg stated that custom shoes are not necessary for patients with Charcot arthritis and partial foot paralysis. Rothenberg stated that OTS shoes can be paired with OTS insoles, which can be heat moldable.

He suggested that they bring in a shoe from WalMart or Kmart to get an insole.

 

 

 

 

Neuropathy

Insoles are often prescribed because of the risk of foot ulcers from neurotic feet. A systematic review done by the University of Plymouth in the UK and published in the 2011 Journal of Diabetes & Its Complications found that insoles are not effective in preventing ulceration.

Joanne Paton (Doctor of Philosophy) is a university lecturer. She and her colleagues culled 342 papers on the topic. The group then selected five papers that met the inclusion criteria. See Table 2. Table 2. Two studies looked at cast insoles made of plastazote. One study measured ulcer relapse rates (Ucciloi), while another measured peak pressure (Mohamed). One study looked at the impact of EVA foam and polyethylene foam (Lobmann), while another examined the effectiveness of magnetic insoles to reduce neuropathic discomfort. (Weintraub). Albert's last study looked at the impact of a TL-2100 graphite cast insole on peak pressure and contact pressure (Albert).

Paton's research team found that insoles could prevent neuropathic diabetic foot ulcers. They reduced the peak pressure below the first and second metatarsals by between 20 and 30%. Other researchers have noted that it is much easier to find evidence in diabetic foot care literature to show a reduction in plantar pressure using footwear and inserts than to prove that this reduces ulceration rates. Uccioli, a University of Plymouth study that examined ulcer relapse, was the only one to close its review. Patients who had an insole or a therapeutic shoe had a 27.7% rate of relapse, compared with the rate for patients who had non-therapeutic footwear but had insoles which was 58.3%.

Paton's team also noted that only four studies had poor methodology (Weintraub was the exception). These weaknesses include insufficient generalizability, bias due to patients not being blinded, poor randomization, and inadequate generalizability. They called on the diabetes healthcare community for more detailed studies.

Insoles could be beneficial in reducing the plantar pressure in diabetic neuropathy foot, she said. Insoles may be useful in areas that aim to lower pressure on the plantar region. It is not clear whether they can reduce the rate of ulceration. Insoles shouldn't be used alone, but as part a strategy to prevent future ulcerations.

A study in the Netherlands supports this recommendation. Insoles made from flat material were found to be more effective in loading the first metatarsal head. This was according to a 2004 paper published by researchers at the University of Amsterdam in Clinical Biology. This offloading process was however different for each patient.

Insole education

Paton's study revealed that insoles should be regularly replaced and re-evaluated. LER interviewed experts to recommend that insoles be replaced at minimum three times per year. This is the maximum amount allowed by Medicare's Therapeutic Shoe Bill. Some patients may prefer to buy all three pairs at one time and then swap them out frequently. Some people prefer one pair.

Ribotsky keeps his insole's expiration date to remind himself of the three-year exchanges he has every year with patients who are eligible under TSB.

He stated, "I also send automated e-mails reminding folks to change their insoles."

Rothenberg is the chair of American Association of Diabetes Educators' foot specialty practice group. Rothenberg said that the group sees high risk patients every quarter, giving them the chance to change their insoles. Rothenberg stated that many patients prefer to buy all three pairs of insoles at once, so they can rotate them throughout the year.

Another study from Paton's University of Plymouth group found that patients with diabetes who are not covered by the TSB may be able to go longer between insole replacements without significantly affecting plantar pressure attenuation. Insole durability was presented at September's International Foot & Ankle Biomechanics conference. The study found that insoles can compress for the first six months but peak plantar pressures don't change for six more months.

Insole materials

Construction with 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