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
Design Description
Problem Statement
Material Selection
Self-customizable Perforated Orthotic for Diabetics
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.
Static Coin
Test
Left foot
The device is composed of four individual, heat-moldable material layers. Using
innovative perforated customizable features each patient will be able to adjust their insert
to meet the specific needs of his or her unique feet. Using a quad-lam (four layer) design
consisting of Thermo-cork (uniformly perforated), Multi-cell Puff (specifically
perforated), Poron, and pink Plastizote (from the bottom up) optimal performance data
was achieved.
15
10
5
0
100
70
200
300
400
500
Left foot coins
600
700
800
600
700
800
Offloading of First Metatarsal Head
Legend – Inserts
60
– New Balance insert
– Tri-lam/
– Tri-lam/ Plastizote base
– Tri-lam/ cork base
– Plasitzote/ Spenco
50
40
20
10
0
0
100
200
300
400
500
Four custom inserts were manufactured with
the help of a certified pedorthist, a foot
device specialist Using the FSM we tested
five inserts (four custom and one factory
insert) to determine which materials
provided optimal offloading. Two coins
were placed under the first metatarsal head
of the foot (for simulated loading). It was
verified that the tri-lam inserts (typically
used for diabetic inserts) provided the best
offloading. Different base layer materials
did not vary a great deal, so Thermo-cork
was chosen because it would be most easily
perforated. A second test explored the
effectiveness of a variety of perforation
schemes. Based on the results, a general
scheme was chosen for the base with a
specific scheme for the second layer.
Cost to Manufacture
In order to accurately calculate the manufacturing cost of our proposed product, the group assessed the costs
of mass production. The materials used in the prototype and the cost of labor for perforating the Thermocork and the multi-cell puff are quantified and exhibited in the table below.
Estimate for 2400 Pairs
Figure 1 shows the typical areas of high pressure
that result in ulceration in the diabetic foot.
a)
b)
d)
c
) diabetic foot deformations and
Figure 2 shows typical
ulcerations. a) a severe ulcer on the first metatarsal
head b) foot drop, which prevents patients from
being able to hold their feet up c) hammer toe, which
increases pressure on a toe after it curls towards the
foot d) Charcot foot, which results in the loss of arch
and increased pressure in the center of the foot.
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.
Design Process
The group met with experts and researched the effects of diabetes and the market for a device to reduce
vertical plantar pressure in patients’ feet. The second phase involved brainstorming and preliminary
testing of materials. A prototype was designed and tested before being modified for final testing and
comparison to existing devices. Safety and cost were considered.
Example Existing Products, Advantages, Disadvantages, and Cost
• Total contact
• Require sizing and modification;
do not provide offloading; not
durable; extra cost to modify
• $20/pair for four month use
Custom Insert
• Maintains total contact and
offloads areas of high pressure.
• Requires intensive labor by a
professional
• $260/pair for four month use
0
30
Ideal Design
Acor QuikFit Pro
Legend - Shapes
- Diamond
- Circles
- Diamonds and circles
20
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, because of 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.
static coins
25
Acor QuikFormables
• Total contact; customizable
• Labor intensive construction;
requires sizing
• Varied prices for four month
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
•$15/pair for one month use
Part
Qty
Price Each ($)
Total ($)
Thermo-cork sheets (Acor)
100
156
15600
Dual laminate sheets (Acor)
100
120
12000
Multi-cell puff sheets (Acor)
100
48
4800
Glue (Rubber Cement)
25
2.50
67.50
Perforations (H and K perforations)
200
25
5000
Labor costs (at 6 pairs/hr)
40
15/hr
600
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. 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.
Cost per Pair
Estimated Cost of Device
Social Impact
The insert was designed to be 3/8” in thickness
and shaped to fit in any standard extra depth shoe.
The Thermo-cork layer was ground to
approximately 1/16”. The Multi-cell Puff was
also 1/16”. The remainder of the thickness came
from the other layers, which were 1/8” each. The
materials that were used are known to have a
useful life of at least four months in current
models, so this application should be similarly
useful. A general perforation scheme in the cork
will allow offloading at any site, and the specific
perforation of the Puff compensates in areas of
typical high pressure. The devices can be quickly
ground to any size during fabrication.
Test 1L Max
30
20
$15.86
$30
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.
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.
Conclusion
50
40
38067.50
Market
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.
F-Scan Vertical Plantar Pressure Testing
A maximum pressure map of the left foot produced
using data obtained from the F-Scan Mobile (FSM)
system is exhibited to the right. The FSM uses a 0.15
10
mm thick resistive transducer to obtain vertical
plantar pressures of the foot during its natural gait
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2
cycle with a spatial resolution of 0.25 cm . This data
was then loaded into Matlab and analyzed using a
30
program created to determine areas of peak pressure
to view regions of interest over the period of the gait. 40
A graphic showing the FSM apparatus is displayed
on the left. This free-moving device measured and 50
relayed plantar pressures between the foot and
60
insert. The FSM data was also used to determine the
efficacy of the final prototype.
Sum
Our group has met its goal of designing an inexpensive and versatile device effective in
reducing vertical plantar pressure by means of customization. We have tested the design using
an F-Scan sensor and have planned a manufacturing process. From the work we have
completed, the device could potentially be manufactured and marketed; however, the project
could be continued in order to develop a “smart” insert to plan and monitor pressure offloading
throughout a patient’s use.
Acknowledgements
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Richard Brown
Nashville Orthotic & Prosthetic Services
Dr. Kevin Robinson
Department of Physical Therapy
Dr. William Dougherty, Dr. Naji Abumrad,
Michele Frisbie, Dr. Horace Watson