Offloading Device for the Reduction of Foot Complications in Patients with Diabetes

1. Offloading Device for the Reduction of Foot Complications in Patients with Diabetes Rod Aliabadi1, Patrick Gonzales1, Michael Osborne1, Colin Smith2 Advisors: Dr. William Dougherty3, Dr. Paul King1, Dr. Kevin Robinson4, Richard Brown, C.O., C. Ped.5 Department of Biomedical Engineering1, Department of Mechanical Engineering2, Department of Plastic Surgery3, Vanderbilt University, Nashville, TN, Department of Physical Therapy4, Belmont University, Nashville, TN, Nashville Orthotic and Prosthetic Services5, Nashville, TN DesignDescription MaterialSelection Problem Statement Four custom inserts were made with the help of a certified pedorthist, a foot device specialist. The left insert was made for a normal foot, and the right was made to compensate for a loaded first metatarsal head. Using the FSM, we tested the custom and New Balance inserts to determine which materials provided optimal offloading. Two nickels were placed under the left first metatarsal head to simulate loading. It was verified in the top figure that the Tri-lam inserts that are advocated in literature provide the lowest maximum pressure. The base materials did not vary much. Thermo-cork was chosen because it would be easiest to perforate and would provide the most structure. A second test explored different perforation schemes in tri-lam with static testing. Based on the results seen in the bottom graph, a general scheme was chosen for the base with a specific scheme for the second layer. Self-customizable Perforated Orthotic for Patients with Diabetes Material Offloading of First Metatarsal Head The physiological effects of diabetes can lead to excessive vertical plantar pressure during normal gait. This pressure can result in ulcerations in the feet of patients and may lead to amputation. Devices to reduce this pressure and prevent ulceration are often very expensive and have limited versatility. Among non-customized products on the market designed to reduce the occurrence of foot ulcerations in diabetic patients, none are a viable alternative to labor-intensive customized inserts. This project seeks to develop such an alternative. The device is composed of four heat-moldable material layers. Using innovative perforation-based customizable features each patient will be able to adjust the insert to meet the specific needs of his or her unique feet without intensive labor costs. After preliminary testing it was decided to use a quad-lam (four layer) design consisting of Thermo-cork (uniformly perforated with diamonds 9/16” per side), Multi-cell Puff (specifically perforated with circles in areas of high pressure), PORON, and pink Plastazote in order from the bottom up. The top three layers are the three materials that compose the diabetic tri-lam that is used in existing products for offloading and heat forming ability. The cork provides unique offloading that is not available on the market without customization. Perforation Shape Determination: Static Test Diabetes and Foot Complications Diabetes affects nearly 20.8 million Americans and is characterized by insufficient insulin production (Type I) or insufficient insulin action at the cellular level (Type II). There is no known cure for the progressive disease, but patients can be treated by insulin therapy to suppress many of the symptoms. As the disease progresses, patients may experience neuropathy, or degeneration of the peripheral nervous system. The resultant loss of sensation is most severe in the peripheral limbs, signifying the loss of muscular innervation and a loss of flexion in muscles of the feet. This results in deformation of the skeletal system, or a loss of skeletal structure, that can lead to areas of high plantar pressure and ulceration. Ulcers can also form as a result of ischemia, a reduced level of oxygen in the blood, becauseof the reduced capacity for healing that results from decreased circulation. Thus, a small injury or infection due to trauma can rapidly progress into a dangerous ulcer without any patient awareness. Preventative devices typically consist of customized insoles that conform perfectly to maintain total contact with a patients foot and incorporate recesses in areas of deformation to redistribute the pressure and prevent the development of ulcerations. Cost to Manufacture In order to accurately calculate the manufacturing cost of our proposed product, the group assessed the costs of producing 2400 pairs of inserts. Expenses from materials, labor, and perforating the Thermo-cork and the Multi-cell Puff are exhibited in the table below and analyzed to determine an estimate for the market price. a) b) Figure 3 shows the basic design of the prototype and the reasoning behind it. On the left is our final design shown from the bottom and the top views. The perforations on the bottom allow the customization demonstrated on the heel in the photos at the top right while maintaining total contact with the foot. The bottom left shows a flow chart that describes the current process of insole customization by a certified professional and highlights the steps that can be made more efficient in order to reduce costs. Evaluation of Inserts-Vertical Plantar Pressure vs. Time This cost is about 13% of the cost for custom inserts and only $10 more per pair than the less robust QuikFit inserts. The insert was designed to be 3/8” at the toes and was shaped to fit in any standard extra-depth shoe of a specified size. The Thermo-cork layer was ground to about 1/16”. The Multi-cell Puff was 1/16”. The other layers were 1/8”. The materials that were used are known to have a useful life of at least four months in custom models. Using a general perforation scheme in the cork allows offloading at any site, and specific perforation of the Puff compensates in areas of typical high pressure. In areas of typical high pressure, like across the metatarsal heads, the diamonds can be split into equilateral triangles to provide more specific offloading. c) d) Market In the United States alone, approximately 1.25 million diabetic patients can be expected to develop peripheral ulcerations related to their disease and spend approximately $30,000 a year on treatment, leading to a multi-billion dollar domestic market to prevent such maladies. The device would also comply with current Medicare legislation to supply customized footwear to all needy patients that suffer from diabetes and its complications. Ideal Design Safety Issues This device is a Class I Device according to the FDA, making approval likely. Concerns include the length of useful life, which could be tested, and improper modification, which could be minimized by warnings and professional training. The ideal design should have minimal thickness (<1/2”) to fit in any standard extra-depth shoe. It should be as durable (4 month useful life)and as effective at offloading as current custom inserts, but it should be customizable at a cost of less than $100 per pair. The insert must be able to be changed over time to compensate for morphological change and be available in all sizes. Social Impact These inserts utilize materials typically used in customized inserts to address neuropathy, calluses, pre-ulcerative conditions, and ulcers. According to Richard Brown, C.O., C. Ped, “The inserts balance and correct joint alignment to optimize gait and act as a critical first line of defense to prevent conditions that occur with patients that suffer the devastating complications of diabetes. The layers with perforations allow clinicians to easily modify the inserts to offload specific areas of the foot without the need for an extensive lab.” This design has immense application in rural and international markets with limited access to the professionals and facilities needed to make custom insoles, and the reduced cost makes effective inserts available to more low-income patients than existing technology. Our Design Process The group consulted experts and literature to learn about the effects of diabetes and the market for a device to reduce plantar pressure. The second phase involved brainstorming and using Innovation Workbench. After preliminary material testing, a prototype was designed and tested before being modified for final testing and comparison to existing devices. Safety and costs were considered. The figure assesses the performance of the prototype, a custom insert of the same materials, and a generic insert during free selected gait. This data is from a region of interest beneath the first metatarsal head that had been loaded to simulate a diabetic foot. The prototype with removed cork (green) reduced vertical plantar pressure as effectively as the custom insert (blue) but seemed to worsen without Puff (red). Perforations present an alternative to customization for pressure reduction. Advantages, Disadvantages, and Costs of Example Competitor Products • Acor QuikFit Pro • Total contact, ideal materials for diabetics per literature • Require sizing and modification; do not provide offloading; not durable; extra cost to modify • $25/pair for 3-4 month use • Acor QuikFormables • Total contact; customizable, choice of materials • Labor intensive construction; requires sizing • Varied prices for 4 month use F-Scan Vertical Plantar Pressure Testing Conclusion The F-Scan Mobile (FSM) system by Tekscan, Inc., shown to the left, allowed the wireless measurement of vertical plantar pressure during free selected gait. The FSM used a 0.15 mm thick resistive transducer to obtain pressures between the foot and insert with a spatial resolution of 0.25 cm2. The data acquired was loaded into Matlab and analyzed using a program created to determine areas of peak pressure in the pressure map, shown bottom left, and allow the analysis of regions of interest over the time of the gait. The FSM data was used to determine the ideal material, ideal perforation design, and the efficacy of the final prototype. Our group has met its goal of designing an inexpensive, versatile device for reducing vertical plantar pressure and the incidence of peripheral ulcerations. This product has great potential to provide an alternative to customization for needy patients without proper health care access. We have tested the design using an F-Scan system and have planned a manufacturing process. From this work, the device could potentially be manufactured and marketed; however, the project could be continued to design a “smart” insert that can monitor vertical pressure during its use. • Gel or Air Filled Insoles • Conforms to foot morphology • Short useful life; no offloading; not total contact; foot can move in shoe; puncture risk, little aid • $15/pair for 1 month use • Custom Insert • Maintains total contact and offloads areas of high pressure, advocated by research. • Intensive professional labor • $260+/pair for 4 month use Acknowledgements Nashville Orthotic & Prosthetic Services Department of Physical Therapy Dr. Naji Abumrad, Michele Frisbie, Dr. Horace Watson