Emerging Concepts In Orthoses For Patients With Diabetes
Dr. Wrobel concurs in regard to understanding the impact of varying activity levels. He recently co-authored an abstract that highlighted the variability in activity quality in a small study of patients with DPN.4 The study found that patient steps per day ranged from 4,013 to 17,856 and combined standing and walking activity ranged from 12 to 34 percent of total activity over two days.
Similarly, Professor Nester notes that the real “wear out date” is a combination of steps taken, loads applied and time passed. “However, the costs of recording this are probably greater than the costs of simply giving a new pair out every three months,” he says.
In addition, Dr. Feit says materials are a factor in changing insoles. Most foot specialists prescribe diabetic orthotics made of Plastazote®, NickelPlast™ and Poron®, according to Dr. Feit. He says these materials are soft and will not maintain their shape for more than three to four months in an active patient.
Why does the Center for Medicare and Medicaid Services (CMS) insist on 3/16 inch as an important thickness for insoles?
Professor Nester says pressure relief will occur with most compliant materials at a depth of 3/16 inch. However, he says it is unknown whether this depth is optimum for all patients. Professor Nester also notes that the depth of the insole is important only if one knows the “space” available in the shoe. Otherwise, he says even a shallow insole can increase plantar pressures in a shoe with insufficient depth or space.
Dr. Wrobel speculates that the CMS probably did not have much data available when it recommended an insole depth and had to rely on expert opinion and bench studies. As he points out, the data suggests that a fully arch contoured inner sole in addition to compliant material reduces plantar pressures more effectively than compliant material alone.5,6
“I believe that (CMS is) trying to prevent doctors and prosthetists from dispensing diabetic orthotics which are inadequate or ineffective,” says Dr. Feit. He notes the difficulty of designing a quality orthotic for an adult that is thinner than 3/16 inch in thickness unless one is using graphite, which is expensive.
What is the future of computer aided design/computer aided manufacturing (CAD/ CAM) for orthoses in people with diabetes?
Dr. Feit says CAD/CAM technology has helped DPMs prescribe orthotics that better conform to the patient’s foot and theoretically may be better in helping to reduce shear forces. He notes the use of experimental portable scanners can enable one to take a three-dimensional scan of the foot without the use of plaster and send the image directly to the lab. Dr. Feit says this reduces the lab time to create the device and helps return the orthotic more quickly to the DPM and patient.
“I think we will move beyond our obsession with static shape of the foot in due course,” says Professor Nester.
He advocates that CAD/CAM will need to combine information on foot dynamics to make any advance in the design and performance of orthoses. Professor Nester notes that his group is currently working on this via the Europe-wide project Special Shoes Movement (SSHOES), which is available at www.sshoes.eu.
While Dr. Wrobel sees some value for CAD approaches, he notes that CAM approaches usually involve the direct milling of one material. He suggests looking at differing materials by region. If one is moving shear from the skin and soft tissues into a layered device, he advocates measuring changes in spatial temporal gait. Dr. Wrobel says patients might compensate by slowing their gait speed and increasing their double support time, changes that physicians might miss if they are only looking to reduce shear.
Dr. Feit is a Fellow of the American College of Foot and Ankle Surgeons, and is in private practice in San Pedro and Torrance, Calif. He is the Past President of the Los Angeles chapter of the American Diabetes Association.