Lateral Osteo-Arthritis Footwear with Energy Reduction
MIE 701-702
Technical Design Report
L.O.A.F.E.R Shoe
Project #F05/F06
Design Review Report
Design Advisor: Prof. Dinos Mavroidis
Design Co-Advisor: Prof. Paul Canavan
Design Team
Lucius Acholonu, Tim Farrell
Steve Mcafee, Niels Van Lohuizen
David Van Tassell
October 23, 2006
Department of Mechanical and Industrial Engineering
College of Engineering, Northeastern University
Boston, MA 02115
L.O.A.F.E.R. Shoe
Design Team
Lucius Acholonu, Tim Farrell
Steve Mcafee, Niels Van Lohuizen
David Van Tassell
Design Advisor
Prof. Dinos Mavroidis
Design Co-Advisor
Prof. Paul Canavan
Abstract
This document reviews the design of an orthopedic shoe for the purpose of reducing
ground reaction forces and internal moment of the knee. The design utilizes a dual
density mid-sole and lateral flare that under heal strike to mid-stance walking positions
generates a lateral wedge of 5 degrees. Studies have concluded that the use of a lateral
wedge insert and a flared heel design, individually, have effectively treated varying
degrees of OA patients. Designs compared include the Dual-Density mid-sole, a Multidensity mid-sole and a Lateral support plate. Numerical analysis using the Evart Motion
Capture system and Biometrics Platform combined with physical testing demonstrated
the reduction of ground reaction forces and internal moment. Benefits include halting
progression of knee OA with out costly medical treatments and doctor visits. Prototype
testing showed a 13.23% decrease in the internal knee moment, along with a 2.67%
decrease in the vertical ground reaction force. This design was deemed a successful way
to combat knee moments, which are linked to the progression of osteoarthritis.
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Table of Contents
i Copyright ....................................................................................................................................................... 4
1 Mission Statement ........................................................................................................................................ 5
2 Introduction .................................................................................................................................................. 6
3 Background ................................................................................................................................................ 10
3.1 Footwear Materials and Manufacture ........................................................................................ 10
3.2 Medical Factors of Osteoarthritis .............................................................................................. 13
3.2.1 Osteoarthritis and Age ............................................................................................. 13
3.2.2 Effects of Repetitive Motion .................................................................................... 14
3.2.3 Weight and Obesity .................................................................................................. 15
3.2.4 Gender’s Effect on Osteoarthritis............................................................................. 16
3.2.5 Effects of Active Lifestyles...................................................................................... 17
3.3 Patent Search ............................................................................................................................. 18
4 Concept Design and Selection .................................................................................................................... 20
4.1 Dual Density Heel ..................................................................................................................... 20
4.2 Multi Density Heel .................................................................................................................... 21
4.3 Varied Angle Midsole ............................................................................................................... 21
4.4 Varus Correcting Lateral Plate .................................................................................................. 22
4.5 Heel Flare Wedge ...................................................................................................................... 23
4.6 Lace Patterns ............................................................................................................................. 24
4.7 Added Cushion in Midsole ........................................................................................................ 24
4.8 Design Selection........................................................................................................................ 24
4.9 Final Concept ............................................................................................................................ 26
4.10 Model Generation and Mold Design ....................................................................................... 27
4.11 Prototype Fabrication and Assembly ...................................................................................... 34
4.12 Corporate Involvement ............................................................................................................ 42
5 Data Collection and Analysis ..................................................................................................................... 44
5.1 Experimental Design ................................................................................................................. 44
5.2 Baseline Test Data..................................................................................................................... 49
5.3 Prototype Test Data ................................................................................................................... 50
5.4 Data Analysis ............................................................................................................................ 54
5.4.1 Baseline Theoretical Biomechanics Analysis .......................................................... 54
5.4.2 Laboratory Data Comparison ................................................................................... 64
5.5 Conclusions ............................................................................................................................... 67
6 Future Recommendations ........................................................................................................................... 69
7 Works Cited ................................................................................................................................................ 70
8 Appendix A – CAD Renderings ................................................................................................................. 72
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Copyright
“We the team members,
Lucius Acholonu
Tim Farrell
Niels Van Lohuizen
David Van Tassell
Steve McAfee
Prof. Dinos Mavroidis
Hereby assign our copyright of this report and of the corresponding Executive Summary
to the Mechanical, and Industrial Engineering (MIE) Department of Northeastern
University.” We also hereby agree that the video of our Oral Presentations ifs the full
property of the MIE Department.
Publication of this report does not constitute approval by Northeastern University, the MIE Department or
its faculty members of the findings or conclusions contained herein. It is published for the exchange and
stimulation of ideas.
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1 Mission Statement
The Lateral Osteo-Arthritis Footwear with Energy Reduction (LOAFER) shoe design group is working in
cooperation with Professor Paul Canavan of the Northeastern University Physical Therapy Department to
develop an athletic shoe to help correct the problems of varus tibial-femoral knee alignment while
alleviating some of the symptoms and slowing the progression of osteoarthritis of the knee.
The goal of the LOAFER Shoe Capstone Design group is to design a shoe that will alleviate the pain
associated with osteoarthritis of the knee while simultaneously reducing the rate of degradation of the joint.
This will be accomplished by producing an athletically based and aesthetically pleasing walking shoe for
the age group ranging from forty to eighty years old at a reasonable cost to the consumer. The shoe itself
will:

Decrease the medial tibial femoral contact stress in a patient with knee varus alignment
(bowlegged)

Soften the impact between the user’s foot and the pavement and subsequently reducing vertical
ground reaction forces.

Control the tibial-femoral angles of the knee joint.

Reduce production costs wherever possible while maintaining a quality product.
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2 Introduction
Osteoarthritis of the knee is a degenerative, painful disease that, left untreated, can have crippling effects on
those afflicted. Unfortunately, nearly every aging person develops knee osteoarthritis to some extent.
Figure 1: Tibial-Femoral Knee Alignments
Knee osteoarthritis is caused by the lateral deflection of tibial-femoral angle, the left to right angle between
the upper and lower leg bones. This outward angle is called a varus tibial-femoral alignment. Figure 1
illustrates the natural, slightly valgus alignment along with more extreme valgus and varus knee
alignments. This causes improper loading of the knee joint and permanent damage to the cartilage. The
progression, from a normal knee to a case of severe knee osteoarthritis is shown in Figure 1. Fortunately,
there are many treatments for the early stages of knee osteoarthritis which commonly do not include
surgery.
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Figure 2: Normal knee vs. fully progressed knee osteoarthritis
Among the methods to alleviate the pain of knee osteoarthritis, the most popular is to begin taking over the
counter painkillers such as aspirin or ibuprofen. This method, while effective at managing pain, does
nothing to eliminate the root cause of the problem. It actually increases the development of osteoarthritis
because it alleviates the pain and the user will walk harder than if they were in pain. In addition, if used as
a long term cure it can have negative effects on the liver.
a.
b.
Figure 3: Common alternatives to knee surgery: (a) orthotic inserts and (b) orthotic footwear
Another option for those with knee osteoarthritis is to purchase orthotic inserts or orthotic walking shoes.
However, both of these methods in their current form have their limitations. Inserts have an extremely
short useful lifespan. Most commercially available models, while useful for increasing comfort, can cause
instability in the shoe which is a major contributor to knee osteoarthritis. Orthotic walking shoes solve the
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problem of skewed tibial-femoral angles, have ideal cushioning, and overall are the best of the non-surgical
solutions for relieving the discomfort of knee osteoarthritis. The largest drawback is a new pair of orthotic
walking shoes can cost several hundred dollars, not including the added costs of doctors’ visits and
evaluations to produce a custom shoe tailored to a patient’s specific needs. Along with their aesthetically
displeasing style, orthotic shoes are not built with the athletic user in mind, offering little to no ventilation
anywhere in the shoe. In this era, there is a clear need for an athletic walking shoe tailored to the user that
will alleviate the painful effects of knee osteoarthritis, and will do so in the style of modern athletic
footwear at a reasonable cost.
Figure 4: Example of a complete knee replacement surgery
The shoe developed by the L.O.A.F.E.R. Shoe design group will fill these criteria. This shoe will absorb
the vertical ground reaction force exerted by the ground on a walker’s skeletal structure in a manner similar
to an orthotic shoe. It will control the tibial-femoral angle of the knee by means of an entirely new method
while maintaining a low cost of production and high level of style.
The market into which this shoe will enter is an untapped source of several billion dollars of revenue
around the globe. There has not been a large amount of research and production within this market in the
past. Many companies have taken smaller approaches to this lucrative opportunity. In searching the web
for competing products, it was found that while there are many patents on file for footwear remedies to
knee osteoarthritis, not many seem to have made the jump into actual production. The large majority of
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products are simply small lateral wedges that can be inserted into any shoe to correct the tibial femoralknee misalignment without any change to the actual shoe. This group’s design is meant to address the
issues of stiffness in the cushioning within the shoe, which these products cannot improve.
The search did not turn up any footwear products that were aimed at helping combat knee osteoarthritis.
The only ailment specific footwear in mass production was for the relief of diabetes symptoms. Many of
these shoes also claimed to help arthritis of the leg and knee, however none of them mentioned any of the
improvements found in the patent search for correcting the knee alignment. In addition, many of these
shoes cost more than $200, which could be out of the price range customers on a fixed budget.
One company that has taken a different approach is Shoes N Feet. Rather than sell shoes designed to
relieve knee osteoarthritis, this company modifies customers’ existing shoes. Services from installing
lateral wedges inside shoes to adding material to the outsole to help stabilize the wearer are claimed to
alleviate the pain from knee osteoarthritis along with a range of other leg and lower back ailments. These
competing methods of alleviating knee osteoarthritis will not be as comprehensive or affordable as this new
design.
Each of these numerous factors have created the need for an athletic shoe that can actively help correct
tibial femoral angles while being resilient, comfortable, and stylish as well. Several designs have been
discussed in brainstorming sessions, all of which should help alleviate the pain and discomfort of
osteoarthritis of the knee.
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3 Background
3.1 Footwear Materials and Manufacture
Athletic shoes are comprised of three distinct sections: the upper, midsole and outsole, as shown in Figure
5. The upper is, as the name implies, the uppermost portion of the shoe. It supports the foot’s lateral and
transverse motion and controls the ankle. The midsole cushions the foot and can, depending on its design,
help control the tibial-femoral angle of the knee. Along with these characteristics, it is the primary
absorber of vertical ground reaction forces. The outsole is the rubber portion of the shoe which makes
direct contact with the walking surface. It provides traction and can, depending on the design of the shoe,
absorb some force in conjunction with the midsole.
Figure 5: Diagram of Athletic Shoe
The design goal of this project deals directly with the material selection and shape of the midsole.
Unfortunately, the materials and the trademark names they are given vary by manufacturer. They are also
proprietary, resulting in very little information being made available to the public. Fortunately, the
generalized types of materials are available to the public and can therefore be discussed, tested and
evaluated for our purposes.
There are four primary midsole material types currently used in athletic shoe production. These materials
are phylon, polyurethane (PU), phylite and EVA (Ethylene Vinyl Acetate) foam. Typically a manufacturer
will use polyurethane formed around their own form of cushioning such as gel or liquid silicon, or different
polyurethane foam. [1]. Polyurethane has proven to be a dense, durable and stable midsole material, [2]
making it an excellent choice for use in the loafer shoe. The midsole is formed by pouring the
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polyurethane into a mold. Once set a polyurethane midsole provides the greatest impact protection, its
level of shock absorption dictated by the material properties. This is why some shoes have softer midsoles
than others, as they are designed for a specific activity. For example, running shoes, while having overall
stiffer polyurethane, have a softer lateral compound and firmer medial compound to help cushion the
runner’s foot during heel strike. Walking shoes tend to be a softer compound to provide the greatest level
of cushioning, while hiking boots are very firm to provide a non-deforming platform on which the hiker
can stand while crossing rugged terrain.
The shoe upper is made from a variety of materials ranging from leather to cloth and many synthetic
alternatives. It is formed by beginning with an unformed sheet of material which is die cut into the shapes
that will form the shoe. These pieces are then stitched or glued together using special epoxies and cements.
The outsole is commonly molded carbon rubber but may, in some cases, be blown rubber. Molded carbon
rubber is stiffer and longer lasting than its counterpart but provides a lower level of traction. It is also
heavier due to its greater density. In many cases, rather than using separate molds, shoe manufacturers will
produce a common mold into which the rubber outsole is formed, the polyurethane being added after the
rubber has set. Otherwise, the midsole and outsole are combined using adhesives. Once the outsole and
midsole are joined, the upper is formed around a foot form called a last. These three basic parts are then
joined by a process called “lasting”, during which they are fused together using adhesives. This adhesive is
a flexible, but permanently adhering cement, epoxy or glue. The basic lasting process is shown in Figure 6
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Figure 6: Lasting a Shoe
Like their midsole counterparts, these adhesives are largely proprietary, but there are publicly available
compounds which meet these standards such as 3M’s 5200 adhesive, shown in Figure 7. This particular
compound bonds permanently to most surfaces but remains flexible after curing. It is also heat and
chemical resistant and entirely waterproof.
Figure 7: 3M 5200 sealant
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3.2 Medical Factors of Osteoarthritis
3.2.1 Osteoarthritis and Age
It has been shown that an increase in the vertical impacts at the foot may be a leading factor in idiopathic
weight bearing joint osteoarthritis. [3] Idiopathic means to have a disease having no known cause and
osteoarthritis is chronic degeneration of the cartilage of the joints, also called degenerative joint disease.
Figure 8 shows how osteoarthritis affects the knee joint by degrading the cartilage that serves to lubricate
the contact areas between the bottom of the femur and the top of the tibia. As this cartilage wears away, the
bone begins to grind, causing swelling and pain.
Figure 8: Effects of Prolonged Osteoarthritis of the Knee
Weight bearing joint osteoarthritis causes a loss of motion in the joint and pain in the joint. This is more
common in late to middle aged individuals. In addition people that have joint osteoarthritis have a higher
mortality rate because they are less active. Some try to use genetics to explain cases were osteoarthritis is
only found in a few joints. There is no data supporting the idea that osteoarthritis is due to a natural aging
process or because of everyday activities. Studies have shown that extended normal use of a joint does not
cause deterioration. In a national health survey relating age to weight bearing joint damage the group aged
33 to 54 only slightly more damage than anyone under the age of 33 but in the age group 55 to 74 damage
to the hip, sacroiliac, and knee joints rose 800%, 360%, and 150%, respectively. This data indicates that
from age 55 on osteoarthritis advances very rapidly. [3]
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Figure 9: Osteoarthritis is much more likely to affect patients over 55 and those with active lifestyles
3.2.2 Effects of Repetitive Motion
By observing skeletal loading it can be ascertained that osteoarthritis develops when load amplitude and
total loading cycle thresholds are passed. The exact process is unclear, but it may be damage to the base of
the cartilage. If one is regularly exposed to hand tool vibrations of moderate amplitude for an extended
period the result will be osteoarthritis of the hands, shoulder, and wrist. Impact from sports usually does
not cause osteoarthritis except in long distance runners who are exposed to high impacts for an extended
period of time. But in the end all current ideas do not explain why osteoarthritis advances rapidly in weight
bearing joints in late to middle aged people. [3]
A study was done with 36 people that met specified criteria according to age group and mobility. None of
them had balance problems and no advanced weight bearing joint osteoarthritis. They all repeatedly
stepped onto a force moment platform to measure impact and they did this with and without shoes. Once
the data was compiled and analyzed obvious correlations were revealed. There was a smaller impact
recorded when the subject was barefoot. Additionally, after the age of 50 there was a large increase in
impact per body weight. From this test it was discovered that an increase in sway, which is a result from an
increase in instability, is positively related to impact when walking. Furthermore, most subjects wore a
soft-soled shoe that impairs stability in all age groups. This may be a reason why one would develop
osteoarthritis around 50 and then have the condition rapidly increase. [3]
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Long distance running puts an increased stress on the subjects’ articular cartilage and subchondral bone by
the repetitive impact load that eventually becomes higher than the physiological limit. In order to be at risk
for osteoarthritis the stresses must exceed a critical level at which the cartilage deforms substantially. After
this threshold the cartilage can take more than 90 minutes to return to its original state. Running loads on
the lower extremities are 4 to 8 times higher than walking. Dynamic muscle action will help absorb some
of this force, especially when muscle fatigue becomes a factor, as it does at the end of every race. [4]
MRI’s have already shown that using fast, short inversion times can accurately show oedema, a build up of
excess fluid, within the bone. This suggests that there has been an increase in bone stresses. With this info
one can use the signs of oedema as a potential marker of increased stress. An MRI was taken of the knees
and hips of marathon runners both before and after a race. Gender, age, and weekly running habits were all
taken into account, along with any prior physical defects that could be found. Each subject that met the
standards was given the same pairs of running shoes two weeks before the race. Then each subject had an
MRI both before and after the race. The most common result was a flat deformity within the knee, with no
subjects retaining a completely normal alignment of the hip. This misalignment is another factor of
abnormal loading to the bones and cartilage. Furthermore, no sign of a comparable difference of marrow
oedema was found between pre and post race. In the end many factors have to be taken into account, from
running style, to the surface used to run on, to the subject’s running shoes. Based on the results of this
study, external impact loading does not create internal stresses on the bone and cartilage that can be seen on
an MRI scan. [4]
3.2.3 Weight and Obesity
Osteoarthritis is the most common type of joint disease and it is the fourth most frequent predictor of health
problems in women and eighth most frequent in men. Osteoarthritis may be caused by mechanical wear,
increased cartilage turnover, incomplete repair, and new bone formation. The knees and hips are the main
joints that are affected by osteoarthritis. Obesity plays a big role its development. When body mass index
is 30 to 35, a person is four times as likely to get osteoarthritis in their knees. In addition, work where
bending at the knees on a regular basis is required increases the risk. There is data that shows a correlation
between osteoarthritis and prior knee and hip injuries. Many other factors are believed to play a role in
developing this disease, including increased vertical impact, declines in balance, and decreased muscular
strength. The goals for managing osteoarthritis are to limit the symptoms and lower the pain, so in some
cases patients undergo hip and knee surgeries up to and including total replacements to help attain that
goal. Wedged insoles have been found to help reduce the pain by acting like shock absorbers along with
certain types of shoes. [5, 16]
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3.2.4 Gender’s Effect on Osteoarthritis
The risk of osteoarthritis increases with age and is twice as common in women as in men. There are a
number of risk factors that have been identified from other studies including obesity, over exercising, knee
joint injuries, and occupational factors. Some experts thought that wearing high heels may be the reason
why women are more prone to developing osteoarthritis but no conclusive evidence has been found. The
life course approach looks to examine the relation between the individuals’ health and the changing social
conditions over time. Women from the ages of 50-70 within 20 miles of an orthopedic hospital, who
reported at least moderate knee pain in the past month, and were scheduled to have a knee operation with
osteoarthritis being the reason for surgery were studied. Their entire life was then examined and recorded
from body weight mass index to smoking to previous cartilage wearing behavior. The only high statistical
evidence was a body mass index of 25 or higher when they were age 36-40. [6]
It has been found that stiletto high-heeled shoes exaggerate knee flexor and varus torques during walking,
which might be relevant to the development or progression of osteoarthritis. This altered strain to the
patella tendon during walking may be important to the development of degenerative joint changes inside
the patellofemoral compartment. An increase in the knee varus torque during the beginning stage of
walking shows that there will be compression forces through the medial aspect of the knee. In animals this
has been shown to lead to degenerative changes in the medial compartment of the knee. Wearing stiletto
shoes for a period of time increases the knee varus torque. In addition, when osteoarthritis occurs in
women it tends to occur bilaterally. Men and women do not have different knee varus and knee flexor
torques so this further suggests that the problem is coming from an outside source. [7]
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Figure 10: Women develop osteoarthritis twice as often as men
3.2.5 Effects of Active Lifestyles
There is every indication that under normal loading conditions a healthy, normal knee joint will continue to
function over a person’s lifespan without any breakdown. [8] When patients do develop osteoarthritis, it
usually only occurs in the medial compartment of the knee. It is believed to be more common in the medial
area because higher loads are seen here in static and dynamic activities. Varus moments and increased
loads within the medial compartment are believed to be responsible for the greater incidence of
osteoarthritis. The varus moment mechanically overloads the compartment, which reduces stability and
leads to abnormal knee kinematics. Laterally wedged insoles have been proven to reduce pain associated
with compartment osteoarthritis by reducing the load and restoring better kinematics, but this is only
helpful in the early stages. Yasuda and Sasaki reported that the insole did not change the femorotibal angle
but it did increase the valgus position at the subtalar joint. They concluded that because of the changed
position the limb was now more upright and this reduced the load in the medial compartment. The insole
helped change the angle of the force through the joint. [8]
When a person is walking or jogging the force that is put on their hip joints is many times higher than their
body weight. The load also depends not only on weight but the speed at which one is traveling as well.
Currently there is no data on the influence of shoes or how the kind of heel strike puts force on the hip
joint. There is some data that indirectly suggests that the kind of footwear may change the forces and
moments acting upon the hip joint. Gait analysis of force over time showed a double peaked curve of the
joint contact force during walking and running, with the first peak coming right after the heel hits and the
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second, stronger peak occurring while pushing off. [9] These peaks will be shown in the data analysis
section of this report.
For the treatment of osteoarthritis, tests have been conducted on manipulating parameters in designing shoe
insoles. Using a wedge insole at varying angles acts as a stimulant to the knee because the ground reaction
forces are inclined, causing the patient to adjust to a new standing/ walking setting. When the patient
attempts to adapt to the new standing environment, changes occur in the balance of standing through
muscle activity, producing a new standing and walking condition. The resulting change in ground reaction
forces alleviates tension in the lateral collateral ligament, the lateral capsule, and the iliotibial tract. An
evaluation of the treatment of osteoarthritic knees using wedge insoles of five degrees showed an increase
in the patients’ walking ability .[10]
Forces and moments acting at the hip joint are influenced by the heal strike. Gait stability plays a role as
well because the longer stride yields higher impact forces on the shoe heel. According to Influence of
Shoes, smooth gait patterns coupled with soft heel strikes were the only experimentally determined method
to reduce joint loading in slow jogging.
3.3 Patent Search
The US Patent and Trademark Office (USPTO) contains a large number of patents that relate either
partially or directly to this project. Many of the patents pertain to the creation of a separate “wedged”
insert or a redesigned insole that may be added to any existing shoe. As this design will incorporate a new
insole, mid-sole, and possibly outsole design as a primary method to correct the gait of the wearer, these
singular methods to correct the problem do not completely cover the project as it is currently outlined.
However, these patents must be taken into consideration as the individual parts of the new shoe will be new
designs, or the relevant patents will be properly referenced.
The next group of patents contains different strategies for redesigning the mid-sole of a shoe for the
purpose of alleviating the symptoms of knee osteoarthritis. These all drive at the heart of this group’s
design, which will be focusing around the redesigned mid-sole. These patents provide valuable
information to assist in the creation of a unique design. Elements of these designs can be incorporated for
their individual merit, while allowing this design to remain separate from those already on file at the
USPTO.
One of the patents in this group is “Shoe Incorporating Improved Shock Absorption and Stabilizing
Elements,” [11] which puts forth a mid-sole design containing “unsymmetrical stabilizing pods disposed
between shock absorbing upper and lower deflectable plates”. This design allows a non-uniform
absorption of impulse over the area of the plates by virtue of shock absorbers of different strengths on the
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inner and outer sides of the sole. The stiffness of each shock absorbing pod can be tailored so the mid-sole
allows the instep to roll inward slightly, maintaining the correct femoral-knee angle to slow the progression
of knee osteoarthritis.
An additional feature that could be incorporated into this design is using different lengths of shock
absorbers on the medial and lateral sides of the mid-sole to create the “wedge” found in many insole
designs. This could allow the shoe to be adaptable to multiple commercial insoles, such as high arch or
odor suppressant insoles.
Additional patents were found that provide methods of treating knee osteoarthritis with external
apparatuses that attach to existing shoes. “Device and Method for Treating Arthritis of Knee” [12]
describes such an item. By attaching a band from the medial side of the ankle to the medial side of the
knee, the design adds additional force to the inner knee area, to help maintain the correct alignment. This
design does not fit well with the desire to create a shoe that is attractive to buyers with minimal extra parts
to differentiate it from any other athletic shoe. Many consumers would be hesitant to purchase a shoe that
has rubber banding extending from it, for both aesthetic and ease of use concerns.
The final patent presented here is one which achieves many of the goals of this group’s project. “Joint
Protective Shoe Construction” [13] details a shoe with a redesigned mid-sole and insole with a taller lateral
side than medial side, creating the wedge needed to correct the knee misalignment. This patent is the most
comparable product to the one this team will create, however it does not provide as comprehensive relief of
tibial-femoral misalignment. In addition, this patent has not been put into production despite the two years
that have passed since it was approved by the USPTO, so it is not competing for any market space.
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4 Concept Design and Selection
Several design concepts were brainstormed, and the best possibilities are included here. The final design
will include several of these designs to capitalize on the benefits of each.
4.1 Dual Density Heel
The dual density heel system is very simple in design, and in fact merely modifies a technique already in
use when constructing footwear. In most running shoes on the market today the lateral or outer side of the
heel is made of a much softer material than the medial or inner side. As this has been shown to increase the
varus misalignment in the knee, the first concept is to invert this pattern. By designing a shoe where the
medial side had a softer or less dense material than the outer side, the foot and ankle would naturally roll
inward slightly. This would help correct the tibial-femoral angle and prevent the progressive damage of
osteoarthritis
Figure 11: Design Concept 1: Dual Density Heel
The ideal design would be one that gradually changes from a material of one density to another. On the
medial side, the sole would be comprised entirely of the softer of the two materials. Moving towards the
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lateral side, the materials would be layered with a gradient, so the overall thickness stays constant while the
percentage of each material changes.
4.2 Multi Density Heel
This design is similar to the Dual Density Heel; however it would involve more than two materials. By
using multiple sections arranged from softest to hardest, the effect could be much more finely tuned. This
would allow for a more sensitive calibration of the adjustment angle. It may also provide for more comfort
because of the less drastic change in hardness from one side of the heel to the other. Unfortunately, it
would also likely be more expensive and difficult to manufacture.
Figure 12: Design Concept 2: Multi Density Heel
4.3 Varied Angle Midsole
The biomechanic effect of placing an angled lateral wedge insole into the shoe effectively adjusts the
subjects gait by pushing the legs inward. [15] The angle of the wedge would be roughly five degrees and
composed of polyurethane. A possible addition to this design would be a cushioned midsole to further
absorb vertical ground reaction forces. This layer would consist of a softer, shock absorbing heel with a
reinforced bridge and toe for stability through the toe swing. This would have the effect of permanently
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installing a lateral wedge within the shoe. It would also allow for this to be a baseline angle, with
additional wedges available for more severe varus misalignments.
Figure 13: Design Concept 3: Varied Angle Midsole
4.4 Varus Correcting Lateral Plate
Slippage between the foot and the insole are a leading cause of shear stresses in the meniscus cartilage.
Both the lateral and medial menisci break down as a result of this abrasive contact. A plastic support plate
installed into the lateral wall of the shoe will both reinforce the outer wall and simultaneously brace the
ankle in place. As the subject applies force onto the heel of the shoe, the tendency is for the leading shoe to
slide outward and forward. This design corrects the side to side motion and reduces likelihood of rolling the
ankle.
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Lateral Support Plate
Figure 14: Design Concept 4: Varus Correcting Lateral Plate
4.5 Heel Flare Wedge
A flat profile of the lateral side of the outsole of a shoe allows the user’s ankle to roll outwards, increasing
a varus alignment. This can be corrected with a slight flare of the lateral sole. By flaring the profile the
shoe’s contact with the ground will force the foot to roll inwards, helping to correct the alignment of the
foot as the ground strike occurs. Studies have shown that a 16 degree angle of flare will have a noticeable
lowering impact on the vertical reaction forces, and will increase the amount of time from the first contact
to the maximum vertical ground reaction force during heel strike. [14]
Flared Profile
Vertical Profile
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Figure 15: Design Concept 5: Heel Flare Wedge
4.6 Lace Patterns
Another angle the group is exploring for the design is how the shoe laces are tied through the sneaker. The
classic method of crossing the laces pinches the shell closing the toe box. This can cause problems as
middle-aged subjects feet tend to swell during activity, and the loosening of their joints allows the toes to
splay out. The smaller toe box can cramp the feet, adding to the discomfort. An alternate method would
allow the foot to expand within the shoe without cutting circulation off above the arch. This would be
achieved by creating a lace pattern that pulls the two halves of the upper directly across towards each other.
The current “criss-cross” design also tends to pull the upper lacing towards the lower, which is the root
cause of the closing of the toe box. This newer method would still hold the shoe securely closed to prevent
slippage, but allow the shoe to expand along with the foot better.
4.7 Added Cushion in Midsole/Outsole
Another additional consideration was to reduce the impulse of the ground strike force. To reduce impulse,
one of two actions must be taken: reduce the amount of force or increase the time the force is dissipated.
As the first option is not applicable, the amount of time it takes for the foot to stop moving must be
increased. This could be done by adding thickness to the midsole or outsole of the shoe, and possibly
making it entirely softer. This way the shoe would have more time to absorb energy before it reaches its
critical compression. This would help reduce the impulse of the ground strike force and limit the damage
done to the knee cartilage when that force is transmitted up along the leg.
4.8 Design Selection
Two of the design ideas were eliminated after further scrutiny. Adding cushion to the midsole or outsole
comes with a distinct risk. Studies have shown that as a person ages, their body’s ability to accurately
judge the distance to the ground deteriorates. This can create a specific problem when a shoe is worn that
has a thicker than average sole. The user subconsciously thinks the ground is going to be at the position it
would be if a shoe of normal thickness is being worn. This leads to a harder step, increasing the ground
reaction force and the contact stresses within the knee. Since this is directly contrary to the aim of this new
shoe, the added cushion design plan was eliminated. The wedged midsole design, while likely to be an
effective means of correcting the varus angle in the knee, is not a very novel design. Multiple patents
already exist for wedged insoles and midsoles for shoes. To ensure that no patent or copyright
infringement occurs, this concept is also being eliminated.
The remaining concepts needed to be compared to find the best option. The designs would be compared on
the basis of comfort, performance, cost, ease of manufacture, availability of parts, durability, and aesthetics.
24
Table 1: Design Concern Comparison Matrix
Goal
Comfort
Performance
Cost
Ease of
manufacturing
Availability
of parts
Durability
Aesthetics
Comfort
—
1/2
1
1
1
1
1
Performance
½
—
1
1
1
1
1
Cost
Ease
manufacturing
Availability of
parts
0
0
—
1
1
1
1
Total
5 1/2
5 1/2
4
0
1
0
—
1
1
1
4
0
1
0
0
—
0
1
Durability
0
1
0
0
½
—
1
Aesthetics
0
1
0
0
0
1/2
—
2
2 1/2
1 1/2
In Table 1, the goals are systematically compared to one another using the following process:

The goal along the row associated with it in the rank-ordering table is given a value of 1 if it is
viewed to be more important than another goal associated with a particular column.

A score of 0 is awarded to a goal if it is deemed to be less important than the column goal.

In any case where there are two goals that deemed to be of equal significant, each is given a score
of ½.
After awarding these values, the goals are listed in the final rank-order according to their total scores (see
the Table 2).
Table 2: Final rank-order of design goals for LOAFER Shoe
1
Comfort; Performance (Tie)
2 Ease manufacturing; Cost (Tie)
3
Durability
4
Availability of parts
5
Aesthetics
Table 2, which contains the relative rank-order of the goals, was used to compile the decision matrix.
Before establishing the decision matrix, a step taken to assign absolute weights of significance to the goals
(Table 3) and also create rating factors (Table 4) for the each alternative concept.
Table 3: Assigning relative weighting factors to goals
Values
Goals
100
Comfort; Performance(Tie)
90
Ease manufacturing; Cost (Tie)
70
Durability
60
Availability of parts
50
Aesthetics
Table 4: Range (1-10) for design rating factor
Values Rating factors
10
Excellent
8
Good
6
Satisfactory
25
4
0
Unacceptable
Failure
Table 5: Calculated Decision Matrix
Design
Alternatives
C1: Dual Density
Midsole
C2: Multi-Density
Midsole
C3: Heel Flare
Wedge
C4: Plastic
Support Plate
C5: Dual Density
Midsole
Heel Flare Wedge
Comfort
Performance
Ease
manufacturing
Cost
Durability
Availability
of parts
Aesthetics
100
100
90
70
60
50
40
Total
5/500
8/800
7/630
6/420
8/480
6/300
8/320
3450
7/700
6/600
6/540
6/420
8/480
6/300
8/320
3360
6/600
7/700
7/630
7/490
7/420
6/300
8/320
3460
6/600
6/600
7/630
6/420
7/420
5/250
8/320
3240
6/600
8/800
7/630
8/560
7/420
6/300
8/320
3630
The decision matrix table is derived by the insertion of the weighting factor for the design goals, together
with rating factors for each alternative concept. Each weighting factor WF is multiplied by the
corresponding rating factor RF for each design, producing what is known as decision factor DF
DF = (WF) x (RF)
4.9 Final Concept
The final concept selected was a combination of several of the initial ideas formulated by the group. As
seen in the decision matrix, combining the dual density midsole and heel flare wedge will create a new
design that is superior to its individual parts. The dual density midsole teams with the heel flare wedge to
create the initial angular correction as the user begins their step profile.
This new shoe was constructed with many parts of an existing shoe, the Converse Southie OX. A pair of
these shoes was deconstructed into its upper, insole, midsole, and outsole. The midsole was scrapped and
replaced by the final concept midsole. This made the design and manufacture of the prototype pair as easy
as possible.
With the help of Converse shoes, along with the previously covered research, this table of relevant design
criteria was developed to drive the creation of a first prototype. Following these parameters will allow for a
midsole design that will work with the remaining parts of the Converse Southie OX shoes, as well as
include the new design ideas developed by this group.
26
4.10 Model Generation and Mold Design
Shoe design is a highly free-form process, into which only rough dimensions are incorporated. These
dimensions are derived from the specific last around which the shoe is formed. Last form was generated
via research in the 1980’s by major footwear companies to generate athletic shoes that best fit a broad
variety of demographics. The resulting forms are still used in industry today. It is from these lasts that all
shoes are generated using various graphics packages including Alias, Rhinoceros and other similar
software. Working with converse and acquiring blueprints of the Southie OX shoe resulted in the
obtainment of overall shoe dimensions which needed to be incorporated into the L.O.A.F.E.R. shoe design.
The required dimensions for this design’s purposes are shown in the specifications table, Table 6, which
lists overall length, toe box and heel width, and overall thickness, in addition to the driving characteristics
of the final design.
Table 6: Prototype Design Specifications
1.)
Length
Size 10.5
280mm
Size 11
292mm
110115mm
2.)
Max. Toe Box Width
110-115mm
3.)
Max. Heel Width
80-82mm
4.)
Heel Curve Start
5.)
6.)
7.)
Toe Curve
Decouple Heel for flex
Dual density heel to split down heel
centerline
80-82mm
30mm from heel of
shoe
Follow Last
Downcurve
8.)
Intended Dual Density Heel Angular
Deflection
5 degrees
9.)
Heel Flare Vertical Angle
16 Degrees
5 degrees
16
Degrees
Before incorporating these dimensions, however, a last had to be created to acquire an accurate model of
the last downcurve, or the lower surface of the last.
27
Figure 16: DAP Plaster used to create shoe last
Last form was generated via research in the 1980’s by major footwear companies to generate athletic shoes
that best fit a broad variety of demographics. The resulting forms are still used in industry today. It is from
these lasts that all shoes are generated using various graphics packages including Alias, Rhinoceros and
other similar software. Working with converse and acquiring blueprints of the Southie OX shoe resulted in
the obtainment of overall shoe dimensions which needed to be incorporated into the L.O.A.F.E.R. shoe
design. Mixing DAP plaster of paris two parts to one with water, pouring it into the shoe and allowing it to
set produced our lasts for both the size 10.5 and 11 shoes. Per the instructions of the plaster, the shoes were
allowed to set undisturbed for two hours. Once the plaster was fully set, the shoes were unlaced and the
lasts removed.
28
a)
b)
Figure 17: a)Forming plaster last inside of shoe and b)finished last next to shoe
The bottom surface of these lasts would then be measured by detailing the length of the last centerline and
taking measurements perpendicular from this line at one inch intervals to the edge of the last. These
measurements generated points in the bottom view upon which a spline could be laid to produce an
accurate curve for the top surface of the midsole. Other measurements included vertical distance from a
level surface to the centerline and edges at the same one inch intervals. Using this three-axis information,
29
the accompanying 3-D form which forms the top of the midsole was accurately duplicated in a 3-D
modeling package.
Initial hopes to have the shoe professionally designed by Converse were dashed by inability to acquire any
size other than men’s size nine and a refusal to work with other measurements due to the complexity
involved. This unfortunately eliminated the ability to have a commercially produced shoe. This led to a
primary attempt at producing a model using Solidworks due to its user friendly interface and extensive
support network within Northeastern University of professors and graduate (and undergraduate) students.
Unfortunately, this package lacked the necessary level of control required to produce an accurate surface
model of the last downcurve. Ultimately, the decision was made to produce the models in PTC’s
ProEngineer modeling package. Solidworks, however, would play a critical role in part generation which
will be discussed later.
a)
30
b)
Figure 18: Progressive creation of a ProEngineer model of midsole
ProEngineer allows for complete form control in all three dimensions and ultimately an excellent surface
model was generated. Major difficulties with this software were resolved by seeking professional
assistance outside Northeastern’s network. Several steps were required to produce the models once the
method was understood. This was accomplished by taking the measurements from the plaster last and
incorporating them into several sketches. First, the top view was produced by generating one inch
construction lines until the required length was attained. For the size 11 shoe, an extra half inch
construction line was added to acquire the necessary length. At the intersection of these points, the
perpendicular, centerline-to-edge information was added, also as construction lines. The lateral and medial
side splines were added next, the ends of which were constrained tangent to one another, thus ensuring
tangency at endpoints and a continuous surface. The next two splines to be created were the sideview of
both the downcurve centerline and downcurve edges. The same process for creating the top view points
was followed to create these accurately. The sideview of the downcurve edge and the top view splines
were then projected onto one another to generate a 3-D spatial curve. This task accomplished, conic arcs
were added between the 3-D downcurve and the 2-D center curve at the same one inch intervals to produce
the required framework for a 3-D surface. Conic arcs were chosen due to ProEngineer’s ability to
accurately surface along them and for their full level of control by choosing the midpoint and approach
angle from the endpoints. Two tangent boundary blends were then mated to produce an accurate surface
model of the last downcurve. The overall contact surface form was generated next, ¾ of an inch below this
curve at its mean height from the theoretical base surface. This was accomplished using a spline offset the
required distance from the downcurve as dictated by the design specifications. This completed, another
31
spline was drawn in the top view (also dictated by design specifications) and the two were projected onto
one another creating a 3-D curve which generated the lower, wireframe edge of the midsole, also called a
surface curve. Individual conic arcs were then drawn between the downcurve and the surface curve to
generate a 3-D wireframe model of the entire midsole. Boundary blends and part fills were then used to
join all the surfaces into a 3-D surface model. This process was repeated for the second shoe size as well.
a)
b)
Figure 19: Finished models of the size a)10.5 and b)11 midsoles
The hard medial heel piece was developed by modifying the existing surface model of the 10.5 and 11 size
shoes. To do so, a sweep was passed through the existing surface from the center point of the heel to an
area approximately three inches forward of the heel. This exit point was chosen for its inherently noncritical location. This sweep was then merged to the lateral heel surface to generate a new part with
identical dimensions to the lateral heel of the midsoles. Again, this process was repeated for both the size
10.5 and 11 shoes.
At this time, the models were fully generated and ready to be exported to Solidworks for mold production.
Solidworks was chosen over the ProEngineer mold function for the same reasons we originally tried to
model using the software. The mold tool in Solidworks allows the user to import a body, form any shape
around it and then remove the body, all in a very user friendly interface. By adding a parting plane, the
solid body is then separated into two halves. These halves were saved as individual part files rather so that
they could be produced on campus. Guide holes with .083” diameters were added to the two halves to
complete the models leaving a fully prepared 3-D part file ready for production.
32
Figure 20: VIPER stereolithography machine used to create molds
These mold files were then sent to a VIPER stereolythography (SLA) machine for production. The VIPER
SLA machine works by hardening layers of liquid polymer. This is accomplished by directing an
ultraviolet laser over the polymer, in a pattern predetermined by a computer model. Each pass made by the
laser will add a very small layer to the piece, stacking up to form the complete part. This machine used
.004” thick layers of resin to produce the molds. Unfortunately, this slow layering process led to a four day
production delay while the molds were created. After ninety-eight hours of mold generation, the VIPER
system completed production.
33
Figure 21: SLA Curing Oven
At this time, while the parts are no longer a liquid, they do not have a hard consistence, and tend to stretch
and deform. To finish the SLA process, the molds were then washed in a solvent and placed in an
ultraviolet oven to complete the curing. The fully prepared molds were then ready to have our various
polyurethane materials added to begin production of the final prototype.
4.11 Prototype Fabrication and Assembly
Before pouring any of the polyurethane epoxies first get access to an air hood. The hood operates much
like a stove hood, sucking any possibly dangerous vapors up away from the user to prevent possible injury.
Inhaling these dangerous gases could lead to respiratory harm and was avoided at all costs. Any materials
within the hood were sealed and set aside or removed completely. The particular polyurethane materials
used in this project had a special caution regarding water and water vapor. Contact with either of these
would cause the chemicals to begin producing carbon dioxide, a dangerous gas that could cause harm to the
user or a pressure burst if the materials were resealed in their containers.
34
Figure 22: Concentrated Ammonium Hydroxide for cleaning polyurethane chemicals
After preparing the work area, a solution was made comprised of .2-.5% liquid detergent and 3-8%
concentrated ammonium hydroxide, shown in Figure 22, in water. This solution was used to render any
spilled chemicals inert, further reducing the risk of injury to this group or any other users of the chemical
hood.
35
Figure 23: Chemical fume safety hood
Several different pieces of safety equipment were used in the manufacturing process due to the volatile
nature of the chemicals being mixed. This included goggles for eye protection and gloves to keep the
material from contacting skin, as any skin contact could lead to permanent chemical burns. The entire
work area and all molds were kept meticulously clean throughout the process of mixing and pouring to
ensure that nothing was contaminated and unused chemicals could not come in contact with any of the
finished products after they had been poured and cured.
36
Figure 24: Safety materials used in manufacturing the prototype
First the harder polyurethane was prepared in the smaller mold. The GSP5550-2 part a and part b, the
molds, mold release agent, paper funnel, small cups for scooping up each material, large cup for mixing, a
stirrer, flat head screwdriver, and a scale were gathered together. Everything was organized in the hood so
that there would be no reaching over materials to get anything or work done over the top of any other
projects. The utmost care was taken to ensure that at no time would the chemicals be tipped or knocked
completely over. The mold halves were first placed face up in the hood and given a liberal coating of Ease
Release 1700 from Mann Release Technologies. This product, shown in Figure 25, was a dimethyl ether
product designed to ease the removal of rigid and flexible urethane foams from molds.
37
Figure 25: Dimethyl Ether mold release agent
The need for this product was discovered after preparing a test mold that was nearly impossible to remove
from the SLA test mold. After discussing the problem with the company, the solution of this product was
suggested. The molds were then reassembled with their respective alignment pins, and a funnel was placed
into the fill holes for the assembled mold. The scale, mixing cups, and stirrer were then collected next to
the assembled mold. Using the scale and small mixing cups, each part of the urethane foam was measured
according to the mixing ratios dictated by the material. These two parts were then were then combined into
a large cylindrical mixing beaker and stirred for several minutes with the glass stirrer. Once it changed to
one uniformed color it fully mixed and the curing process had begun. The curing process proceeded quite
rapidly, so the material was quickly transferred into the funnel. The mixture then had to be pressed through
the funnel and into the mold. The lids were immediately replaced on the material cans and sealed down to
38
prevent any contamination or further vapor release. The decontamination solution was used to clean any
part of the hood or any tool that had been in contact with the mixture or either part. All of the cleaning
materials and tools were then left under the still running hood to make sure that any vapors left over would
not be allowed to leave the hood area.
Figure 26: Molds with release agent and polyurethane material
The urethane used for this project requires at least a 24 hour curing time. Attempting to separate the mold
before this time has elapsed would result in more than one problem with the prototype. The polyurethane
would not have fully cured, and would therefore be very spongy and therefore prone to tearing and
deforming from its intended shape. In addition, one of the requirements for the function of the mold
release function is for the polyurethane foam to be completely cured. If the foam was not cured, the mold
release would not function properly and the foam would adhere to the mold, making it nearly impossible to
separate the mold and remove the prototype intact. After the curing time passed the molds were removed
from the hood and transferred to a workbench area. A razorblade was carefully inserted between the two
mold halves to begin to break the seal between them. The blade was rotated completely around the edges
of the mold to make space to fit a small flathead screwdriver. Using the screwdriver to lightly pry a space
between the two mold halves, the prototype was checked to see if the material is fully cured before
separating the top and bottom of the molds. Once one side of the mold was removed from the cured
polyurethane the prototype was carefully pried from the other side of the mold, making sure that all parts
were removed completely.
39
Figure 27: Filled Molds
After pulling the small heel piece from the mold it was lightly sanded to ensure a good bond with the
second polyurethane material. The process of preparing the molds and materials for the larger piece was
repeated with the GSP4030. The only thing different was that the cured piece of gsp5550-2 was put inside
the mold after it was sprayed. This way the gsp4030 bonded to the cured piece of gsp5550-2. After this
new assembly fully cured the new prototype midsole was completed.
Figure 28: Separated Molds with completed prototype
The next step was to assemble the new prototype midsole into a full shoe. Since the Converse Southie OX
was the shoe being used for the basis of the project, another pair was purchased to leverage parts for the
prototype. The midsole and outsole of the shoe were separated from the insole, slip guard, and upper and
discarded. Initially, it was considered to incorporate the outsole as a part of the new design, but several
disadvantages were found to this approach. From a design perspective, modeling the inner side of this
outsole to allow it to mate with the prototype midsole would be nearly impossible. The midsole outsole
40
were not designed specifically by Converse, but rather bought from a Chinese company and delivered as a
single item. While Converse was willing to share their drawings and design information, obtaining the
same information from this vendor was not possible. Additionally, the design of the lateral flare would
need to allow it to envelop the outsole in order for this flare to be the first thing to contact the ground while
walking. This type of design was not going to be possible with the time and resources allotted, so the
decision was made to make the midsole a dual purpose piece. This has been done before with shoes
designed specifically for indoor use. As this was a prototype meant only for lab testing, this was deemed
an adequate solution.
The final steps in completing the construction of the prototype shoe were to reassemble the leveraged parts
of the shoe, insert the previously formed last, and adhere the prototype midsole to the upper assembly. The
plaster last piece was inserted through the bottom of the shoe, followed by the insole and slip guard. These
were then set aside while the prototype midsole was prepared for final assembly. The midsole was first
cleaned thoroughly to remove any foreign particles that could interfere with the adhesive or testing process.
The midsole was then lightly sanded in the areas that would be adhered to the upper assembly. Then a
coating of 3M 5200 sealant was applied to those areas. Immediately, the midsole was joined to the upper
assembly and set to hold fast. At this time it was discovered that the toe portion of the prototype midsole
would not contact the toe area of the upper assembly, so a clamp was attached to hold them together.
Finally, a bead of 5200 sealant was applied around the seam between the midsole and upper assembly to
seal the contact area closed, ensuring that no foreign objects could become lodged in there. The 5200
sealant was left to cure for 24 hours, the recommended time for a complete cure. At this time the prototype
shoe was complete and ready for testing.
41
Figure 29: Completed Shoe Prototype
4.12 Corporate Involvement
The decision was made to involve a major shoe manufacturer in the design and manufacture process once a
preliminary design had been created. The company brought in was Converse Shoes. This was one of the
chief factors in the selection of the Converse Southie OX as the basis for the shoe construction.
Figure 30: Converse Southie OX
Bringing a shoe company into the project will help in many ways with its completion. A local shoe
company would be able to provide contacts for inexpensive manufacturing, as well as accurate figures for
cost of production analysis. In a single production run of the Converse Southie OX, the manufacturer
produces 43,600 pairs of shoes at a cost of $0.50 per pair. While the custom midsole design increases the
cost per pair of shoes, it will not eliminate the profit in the markup of the shoe’s price.
The most relevant reason to involve an outside company was that an established shoe company would have
infinitely greater experience in the basic design and manufacture of footwear.
42
a)
b)
Figure 31: a)Drawing received from Converse for Southie OX with close-up of b)sectional view
(Converse Proprietary Information, DO NOT DISTRIBUTE)
This experience was used to refine the prototype design, making it more marketable, easily manufactured,
or more effective. With the group’s, and by extension the University’s, claim on the initial idea has been
cemented, there are many compelling reasons to bring outside companies into the project.
43
5 Data Collection and Analysis
5.1 Experimental Design
The data collection in part involves the use of a Biomechanics Platform set supplied by Advanced
Mechanical Technology, Inc. The platforms used in these trials were AMTI models OR6.6 and OR6.7.
The platforms are capable of measuring the force components as well as the moment components along the
X, Y, and Z axes.
Figure 32: Force Platforms from the Physical Therapy Lab in Robinson Hall
These reaction forces are measured through strain gauges which are connected to proprietary load cells near
the corners of each platform. The strain gauges form six Wheatstone bridges; output signals from which
three are proportional to the forces parallel to the three axes and the other three are proportional to the
moments about the three axes. The program NetForce, also from AMTI, compiled this data and outputted
text files with these forces and moments.
44
Figure 33: NetForce program performs data acquisition from Biomechanics Platform
These force platforms were used to obtain several key data sets. They provided the ground reaction forces
on all three axes, taken both while stationary and while walking. For this investigation, emphasis was
placed on the ground reaction force in the z direction, or the vertical ground reaction force. This data
helped to analyze how the new design affected the forces at the ground. The important factor was to ensure
that no increase in vertical ground reaction force, and by extension medial knee moment, was found after
the shoes have been altered.
In addition to the AMTI platforms, motion analysis equipment was used to analyze the gait patterns of
normal subjects against those with the bow-legged stance.
45
Figure 34: Motion Capture test camera setup
Five EVaRT 5.0 video cameras manufactured by Motion Analysis Inc. were set up around the
biomechanics platform apparatus to capture still images in the front and side planes. From this the subject
was modeled in three dimensions which provided a visualization of the gait correction – most notably in the
frontal plane view.
Figure 35: (a) EVaRT Motion Capture Camera and (b) Various Sized Markers
46
The motion capture equipment was used to directly measure the tibial-femoral angle in the knee. This is
the most important variable to decrease the contact stresses in the medial compartment, and must be
accurately measured. The two main components, the motion capture camera and position markers, are
shown in Figure 35.
a)
b)
Figure 36: a)Attaching the reflective markers and b)final marker position ready for testing
The equipment works by bouncing light from led bulbs off the highly reflective markers that are attached to
the subject’s body. Cameras, which contain the leds, then record this light and that information is
47
interpreted by the computer to create a picture of the relative positions of all markers in three dimensional
space.
Figure 37: Motion Analysis program for data acquisition from motion capture cameras
The configuration of the markers on the legs determined the accuracy of the tests. For this reason, the
marker configurations were modeled after previous tests in published studies. The setup used included one
marker on the medial and lateral sides of the ankle and knee. In addition three markers were attached along
the front of the knee, with one resting on the kneecap, and the other two five centimeters above and below
that one. Finally, three more markers were placed on the shoe itself, one over the big toe, one over the
pinky toe, and one on the back of the heel. [14, 15] The program Motion Analysis, shown in Figure 37,
was used to translate the data from these cameras to x and y coordinates, which then were used to
determine the angles between the center of pressure and the center of the angle, then the center of the ankle
and the center of the knee. The importance of these angles will be discussed in the data analysis section.
48
5.2 Baseline Test Data
Baseline data was obtained from a member of the design team. The baseline tests were completed while
wearing an unmodified pair of the Converse Southie OX shoes that were chosen as the basis for the new
footwear design. The data obtained was crucial for determining the specific design parameters of the new
shoe.
Gait Force Analysis Fz vs. Time
200
180
160
Force (lbs)
140
120
100
80
60
40
20
0
0
1
2
Right Leg
3
Left Leg
5
4
6
7
8
9
10
Time (s)
Figure 38: Gait Analysis Platform in Physical Therapy Lab of Robinson Hall
In Figure 38 the force data over time was compiled to show the gait patter of the test subject walking across
the platforms. Note the double peaked curves mentioned earlier, both of which were approximately equal
to the subject’s weight. This curve is the result of the maximum heel strike contact force and the forefoot
push off force. The force data was taken using several different test configurations. Dynamic tests were
taken by walking across the platform, while static tests standing first on both feet, then each individual foot
were performed. Figure 39 shows a static setup, with the subject balancing on his left foot for the duration
of the testing. The minute fluctuations in the force can be attributed to the subject balancing himself on the
platform, with the average reaction force equal to the subject’s approximate weight, 170lbs.
49
Left Leg Static Force Analysis Fz vs. Time
200
180
160
Force (lbs)
140
120
100
80
60
40
20
0
0
2
4
6
8
10
12
Time (s)
Figure 39: Baseline test results of static vertical force vs. time
This weight, along with the maximum force of 180 lbs in Figure 39 will be important in the determination
of the internal forces and moments in the knee. Additionally, the motion capture equipment was used to
determine the alignment of the knee and ankle relative to each other and the ground. This data is discussed
further in the Data Analysis section.
5.3 Prototype Test Data
The prototype was created from a Converse© Southie OX sneaker with the factory midsole removed and
replaced with the dual density midsole. Static analysis tests were run using the Biomechanics Platform and
Motion Analysis Equipment and the ground reaction components and the internal knee moment were
calculated.
50
Prototype Static Force Analysis Fz vs. Time
200
180
160
140
Force (lbs)
120
100
80
60
40
20
0
0
2
4
6
8
10
12
Time (s)
Figure 40: Static stance prototype data
On heal strike the test subject reported to notice the inward push from the uneven compression in the dual
heal as designed. Because of the ground reaction occurring at an angle, as shown by the slight xcomponent in the reaction force at the heel, a slight force in the x-direction was induced in the knee. This
lateral force in effect reduces the compression on the medial side of the knee which lowered the moment in
the meniscus. There was also a definite decrease in the ground reaction force over time. Figure 41 shows
the gait profile of the baseline and prototype shoes from their respective tests.
51
Prototype Shoe Left Leg Gait
200
180
160
140
Fx (lbs)
120
100
80
60
40
20
0
0
1
2
3
4
5
6
7
8
9
Time (s)
Prototype Testing
Baseline Testing
Figure 41: Graph showing the baseline and prototype gait profiles
The gait profiles at first glance appear to be nearly identical, but closer examination reveals some major
differences. Figure 42 overlaps the two gait profiles, showing the two major changes in the gait of the
subject using the prototype shoe.
52
10
200
180
160
140
120
100
Heel Strike
80
60
Increased Gait Time
40
20
0
4.8
4.9
5
5.1
5.2
5.3
Prototype Test
5.4
5.5
5.6
5.7
5.8
Baseline Test
Figure 42: Overlay graph of the baseline and prototype gait profiles
The vertical ground reaction force at heel strike does not reach as high a value in the prototype test as it did
in the baseline testing. Calculated values of the ground reaction force and the internal meniscus moment
for the prototype are 779.29 N and 24.0 N-m, respectively. Additionally, there was a .041 second increase
in the gait period. This value is important because it allows more time for the energy of the impact to be
dissipated.
The measurements reflect the design criteria and the decision matrix used to create a prototype where the
variable densities of the two polyurethanes would clearly compress differently under a given load. The
midsole was prototyped such that the heel flare extended over the outside, harder polyurethane and
integrated a softer polyurethane of narrower width on the inside section. The effect of having a flare over
the harder material is to shift the center of pressure on the heel strike towards the outside of the shoe. The
inside, soft polyurethane of narrower width allowed for compression to occur further away from the center
of pressure which assisted in inducing the desired five degree angle range.
A free body diagram illustrating the described reactions is shown in Figure 43.
53
779.2929N
4.192cm
2
24.00N.m
45cm
779.2929N
8.848N.m
1
8.848N.m
1
779.2929N
7.13cm
1.1118cm
779.2929N
Figure 43: Free Body Diagram of the prototype reactions
5.4 Data Analysis
5.4.1 Baseline Theoretical Biomechanics Analysis
An analysis of the biomechanical theory driving the design was performed independent of the laboratory
prototype testing. This data and analysis was used both to confirm the engineering hypotheses, as well as
to compare with the prototype testing to determine the efficiency of the chosen design. This analysis was
used to model the reactions that would occur between the ground and the subject’s knee. This would
include reactions between the shoe and the ground, the shoe and the subject’s ankle, and the subject’s ankle
and knee.
54
FY2
XKnee
2
Knee Joint
FX2
Segment 2
FX1
1
FY1
Ankle Joint
FY1
FX1
Segment 1
1in
Figure.1a
Figure.1b
Figure 44: a)Anatomical link diagram and b)free body diagram from the ground to the knee
Forces acting on the link-segment model
1.
Gravitational forces: The forces of gravity act downward through COM of each segment and are
equal to the magnitude of the mass multiplied by the acceleration due to gravity (normally
9.8m/s).
2.
Ground Reaction or External Forces: Any external forces must be measured by a force transducer.
Such forces are distributed over an area of the body (such as GRF under the area of the foot). In
order to represent such forces as vectors, they must e considered to act at a point that is usually
called the center of pressure (COP). A force plate was used in this case to calculate the COP.
3.
Muscle and Ligaments Forces: The net force of muscle activity at a joint is calculated in terms of
net muscle moments. If contraction is taking place at a given joint, the analysis yields only the net
effect of both agonist and antagonistic muscles.
Joint Reaction Forces and Bone-on-Bone Forces
The three forces described in the preceding sections constitute all the forces acting on the total body system
itself. However, our analysis examines the segments one at the time and therefore must calculate reaction
between segments. A free body diagram of each segment is required as shown in the figure. Here the
original link-segments model is broken into its segmental parts. For simplicity, we make the break at the
joints and the forces that act across each joint must be shown on the resultant free body diagram. This
procedure now permits us to look at each segment and calculate all unknown joint reaction forces. In
55
accordance with Newton’s third law, there is an equal and opposite forces acting on each hinge joints in our
model.
Segment 1 (ankle joint) Reaction Analysis
In a static situation, a person is standing on one foot on a force plate, the ground reaction force is found to
be 2.6196cm from the ankle joint. Note convention has the ground reaction force
FG always acting
upward.
Segment 1 motion equations
For static analysis sum of the forces in the X and Y direction is equal to zero. Similarly the sum of the
moments about any joint is equal to zero.
 FY  ma y
FG  Fy1  0
Fy1  FG  800.68N
Moment about point 1 is zero
 M  I1 1
M 1  FG X ankel  0
M 1  FG X ankle 
M 1  800.68 N  2.6195cm   2097 N .cm
M 1  20.97 N .m
The negative sign means that the moment is in the clockwise direction.
56
800.68N
20.97N.m
1
7.13cm
2.6196cm
800.68N
Figure 45: Free Body Diagram of Segment One showing reaction forces
Segment 2 (knee joint) Reaction Analysis
Similarly for segment 1 motion equation, all the sum of the forces about the X and Y direction is equal to
zero and the moments about any point is equal to zero.
 FY  ma y
FG  Fy1  0
Fy1  FG  800.68N
Moment about point 2 is equal to zero
 M  I 1 1
M 2  M 1  Fy 2 X knee  0
M 2  M 1  Fy 2 X knee
M 1  FG X ankle 
Fy 2  FG
M 2  FG X ankle   FG X knee
M 2  FG  X knee  X ankle 
M 2  800.68 N 6.0744  2.6196 cm
M 2  2766 N .cm  27.66 N .m
57
800.68N
6.0744cm
2
27.66N.m
45cm
20.97N.m
800.68sin5N
1
800.68N
Figure 46: Free Body Diagram of Segment Two showing reaction forces
Design Analysis
The calculation for the knee joint reactions was based on coronal view data for a normal shoe. In looking at
the loads over the knee joint, the GFR of the body runs from the center of the T10 vertebra to the lateral
aspect of the foot in the coronal plane.
58
Figure 47: Coronal view of the Ground Reaction Force
Opposed to the modified mid-sole design the normal shoe has a uniform density for the mid-sole. In this
case we have the ground force reaction in the upward direction. The dual density for our design introduced
forces in the X and Y component. In the monopetal stance the mid-sole deforms about an angle and the
pressure will be distributed perpendicular to the surface as shown Figure 49. The pressure was converted to
concentrated force at a location 1/3 of the base from point a. 1 inch thick foam was used. The length of the
foam is 4 inches which was the calculated breadth of the foot.
W=200.17Ib/in
1inch
Uniform Density
4iches
2 in
2 in
800.68N
Figure 48: Force Distribution of a uniform density midsole
59
1inch
Back View of
The left foot
W=45Ib.in
1in hard
L=1/3(b) =
1.338in
L
hard
soft
b soft
1in
4in
n
a
800
N
Lateral
side
b = 4/cos5 = 4.01528in
Medial
side
б = 4tan5 = 0.35in
x
L
1in
X = Lcos5 = 1.3329in
s = (1-б)Tan5 = 0.05687in
s
x
a = s + x = 1.4in
a
Larger view
Figure 49: Force Distribution of modified midsole with new center of pressure
60
All the dimensions of the foot and breath were calculated from the standard anthropology of the body
shown in
Figure
50. Where all the segment’s lengths, width and breadth where expressed as a fraction of the
subject’s height (H). In our case, the subject’s height was 6ft. The foot length, breadth and height were
found to be 27.8cm, 10.06cm, and 7.13cm respectively. Furthermore, the leg length was found to be 45cm.
61
Figure 50: Diagram of the anthropology of the human body [17]
The force is decomposed into X and Y component using assume angle of 5 degrees. This moved the
position of the center of pressure 30% towards the ankle joint (medial direction) thereby reducing the
moment arm of the GFR which reduces the moment at the ankle. Based on the calculation, the moment arm
of the ankle (Xa) and Knee (Xk) for the modified mid-sole is 70% of the normal mid-sole. The soft side is
the medial side while the hard side is the lateral side and the mid-sole were assumed to have 0.35 inch
maximum deflection.
Segment 1 (ankle joint) Reaction Analysis
In static situation, the sum of all the forces and moments at the joint is equal to zero. The ankle moment
arm is 0.7Xa, and the GFR is acting at angle of 5 degrees upward. This force was decomposed into X and
Y components, which were found to be approximately 70N and 797.6N. The moment at the ankle joint was
found to be -14.29N.m, the negative sign shows that the moment is acting in the clockwise direction.
Segment 2 (knee joint) Reaction Analysis
62
Similarly, all the forces and moments at the joint are equal to zero. The knee moment arm was assumed to
have moved 30% to the ankle joint. The knee moment arm is 0.7Xk, and the forces in the X and Y
components are equal in magnitude with the force acting in the ankle joint. The moment in the knee joint
was found to be 18.84N, which is about 20% reduction in the abduction moments.
0.7XK
45cm
1in
Lateral side
Hard
Soft
0.7Xa
ground
FG
Figure 51: Diagram of double segments showing GFR, and ankle and knee moment arm, with an angle of
deflection of 5 degrees
This is a coronal view of the two segments showing the impact of the dual density of the mid-sole towards
the ankle and knee. The lateral side is denser than the medial side which is labeled soft in the diagram.
During mid-stance the foam deforms exponential. The soft region deforms more than the hard region
causing the GFR to move towards the ankle. The GFR was broken down in its horizontal and vertical
components. Figure 52 below shows magnitude of all the forces.
63
800.68cos5N
4.252cm
1in
800.68sin5N
18.84N.m
45cm
9.63N.m
800.68cos5N
14.29 N.m
1
800.68sin5N
1
800.68sin5N
800.68cos5N
7.13cm
1.834cm
800.68sin5N
800.68cos5N
Figure 52: Complete free body diagram of the two segments showing all the forces and moment acting on
the ankle and knee joint
The force and moments at the ankle was found from static analysis, and then using joints analysis the knee
reactions were found. The foot link was disjointed and from Newton’s third law of motion which says
action and reaction is equal in magnitude and opposite in direction the forces and moment in the foot
segment was transferred to the leg segment and was used to calculate the forces and moments at the knee
joint.
64
800N
797.6N
27.66
N.m
18.84 N.m
70N
0.7xk Cm
xk Cm
45Cm
45Cm
Xa = Distance from GFR
to ankle Joint.
Xa = 2.6195 Cm
14.29
N.m
20.97 N.m
7.13Cm
7.13Cm
Uniform
70
N
Xa Cm
Soft Hard
Xk = Distance from the
compressive
Force at the knee joint to
the ankle joint.
Xk = 6.0744 Cm
0.7xa Cm
797.6N
800N
a)
b)
Figure 53: Side by side comparison of reactions for a shoe using a a)normal and b)modified midsole
5.4.2 Laboratory Data Comparison
Base line data for the Converse© Southie OX sneaker was conducted using a static analysis. The
equipment used for this acquisition was a pair of Biomechanics Platforms and Motion Analysis Cameras.
Motion analysis was used with markers on the foot, heel, and all sides of the knee in order to observe the
shift in position of the medial side. The motion analysis provided three dimensional coordinates of each of
the test points which allowed for the calculation of the lever arm that is a component of the internal
meniscus moment and the ankle. Base line data for the ankle to knee moment arm and meniscus moment
was calculated to be 6.0744cm and 27.66N-m, respectively. This shift occurred when the test subject went
from standing still on both feet to standing on one leg. Previous studies demonstrate the difficulties a
subject has in balancing on one foot with any measure of knee osteoarthritis. Before testing the prototype
the theoretical calculations were performed to see the lever arm shift and calculate the moment under
normal stress with. The calculated ground reaction force for the test subject was 800.68 N. Additional
reactions were calculated at the ankle to be a lever arm of 2.6196 cm and 20.97N-m.
Theoretical values for the prototype were calculated assuming the test subjects body weight and the
induced heel strike angle to be 180lb. and 5 degrees, respectively. Super-positioning those values onto the
65
free body diagram of the ankle and knee shown yielded a theoretical knee moment/ ankle moment arm to
be 4.252 cm and 1.834 cm. The corresponding theoretical knee/ankle moments induced were 18.84 N-m
and 14.29 N-m.
Prototype data was measured following the exact procedure as the baseline measurements. A minor but
negligible discrepancy between both trials is within the placement of the motion cameras. Though it is
impossible to place and angle the cameras in there exact orientation and location for two different
experiments, the ground reaction platform is fixed to the ground. Calibrating the equipment set the origin
at the center of the first platform, which didn’t change in either trial; therefore the measurements were
controlled in the setup. The same test subject was used for the prototype acquisition.
Static analysis of the L.O.A.F.E.R demonstrated that on shifting to one foot the test subject, while
maintaining balance experienced an inward force. This x-component is the result of the dual density heel
on the ground reaction which had both an ‘x’ and ‘y’ component. Therefore it was demonstrated that the
moment arm was lowered when the shift in stance from one leg to standing only on one foot. The ankle to
knee moment arm for the prototype was calculated to be 4.192 cm, and the center of pressure to ankle
moment arm was found to be 1.1118 cm. These represent a 31% reduction in the ankle to knee moment
arm and a 58% reduction in the center of pressure to ankle moment arm. The corresponding internal
moment was 24.00 N-m, with the ankle moment observed to be 8.848 N-m. The reduction observed in the
meniscus moment was approximately 13.2%. Data for the baseline and prototype measurements, as well as
those calculated theoretically are shown in Table 7
Table 7: Comparison of the Baseline, Theoretical, and Prototype test results
Baseline
Theoretical
Prototype
Theoretical
Reduction
(1) Center of Pressure
2.6196 cm 1.834 cm
1.1118 cm
30%
to Ankle moment arm
(2) Ankle to Knee
6.0744 cm 4.252 cm
4.192 cm
31%
moment arm
(3) Ankle moment
20.97 N.m 14.29 N.m
8.848 N.m
32%
(4) Knee moment
27.66 N.m 18.84 N.m
24.00 N.m
32%
(5) Vertical ground
800.68 N
797.6 N
779.29 N
0.3 %
reaction force
Prototype
Reduction
58%
31%
58%
13.23%
2.67%
The measured prototype data compared against the theoretical values for the prototype revealed that our
hypotheses for a higher moment reduction in the ankle and a lower moment reduction in the knee were
correct but numerically off. The theoretical value for the knee moment was calculated to be 19.29 N-m
however we measured 24.00 N-m. The hypothesis was that the prototype shoe would reduce the moment
in the knee by 31%. Testing the prototype we observed a reduction in the knee moment, however the
measured a reduction of 13.23%. Additionally, the theoretical calculation for the ankle moment was
66
14.63N-m against a measured value of 8.848 N-m which corresponds to a theorized reduction of 31% but
measured reduction of 57.81%.
The prediction was correct as to the trend of the prototype data but the magnitudes of the measured values
were surprising. Observing a lower moment in the ankle than calculated is mainly a result of the heel flare
being unaccounted for in the theoretical calculations. Because the flare offsets the center of pressure, it
creates an additional change on the moment arm for the ankle. The load is of relative higher magnitude
compared against the lever arm so even the slightest increase in that length would greatly offset the
magnitude of the moment at the ankle.
The reduction of the knee moment was successfully lowered by 13.23%, however this value underscores
our prediction to attain a reduction of 30.26%. A large contributor to this source of error was in assumed
material properties and mixing. The polyurethane used was tested with the Ingstrom machine which took
the value to be for a homogenous material. The polyurethane was a two part mixture and after curing
showed visible air bubbles, therefore was not homogeneous. This defect in the material composition would
impact the measured value of the moment. Additional sources of error for this project are discussed in the
conclusion section.
67
Calculation based on testing
800.68
6.0744cm
779.2929N
2
4.192cm
27.66N.m
24.00N.m
45cm
45cm
9.18N.m
800.68N
779.2929N
8.848N.m
1
20.97N.m
2
1
8.848N.m
1
1
800.68N
779.2929N
7.13cm
7.13cm
2.6196cm
1.1118cm
800.68N
779.2929N
Modified
Original
Figure 54: Comparison of baseline and prototype free body diagrams
5.5 Conclusions
This project proved to be quite a success. The design goal set out at the beginning of the project was
reached at the conclusion. The initial intent was to lower the internal moment of the knee. The belief is
that this reduction will directly effect the progression of osteoarthritis of the knee. There was a definite
reduction shown in the knee moment, as well as the ground reaction force by this design. As the testing
showed, there was a 13.23% reduction in the internal knee moments. This affected change was not quite as
great as the theoretical reduction of 31.89%. Additionally, there was a 2.7% reduction in the ground
reaction force, most likely due to the increased gait time allowing for the energy of the step to be absorbed
more easily.
There are many possible sources of error that can account for the shortfall from the theoretical reduction in
knee moments. Most likely to blame is the manufacturing process. This material did not cure as a
68
completely homogeneous solid. There were many air bubbles within the polyurethane foam that could
have changed the characteristics of spring and damping. Additionally, the testing itself was not a precise as
desired, due to restrictions in time, budget, and equipment. Ideally, a blind study would have been
performed with many subjects using duplicate prototypes in a number of test repetitions. This would
ensure that the testing that was done was not an outlier. It is conceivable that with more tests of the current
prototype the theoretical reduction could be approached or reached. The somewhat crude analysis methods
could also be to blame. The analysis was not carried to the greatest amount of complexity possible, as it
was not deemed necessary at the time. The intent was to show that the footwear was a viable alternative to
surgery and costly orthotics, and that hypothesis was proved.
The evidence provided in this report shows that changing the lateral angle of the midsole of a shoe
combined with the addition of a 16 degree lateral flare will result in a reduction of the internal moment of
the knee as well as the vertical ground reaction force.
69
6 Future Recommendations
Following the data acquisition and analysis components of the Lateral Osteoarthritis Footwear with Energy
Reduction Design prototype, a number of advances and efficiencies in the development of this product are
recommended. Foremost is the use of an all encompassing, free form software capable of creating the
midsole, exporting it to be molded using any number of stereo lithography techniques and running finite
element analysis. A limitation we encountered in the project was using Pro-Engineer for the modeling
phase and then imported that data to Solidworks in order to create the mold. From there we would have
then used the Solidworks file in Ansys in order to do the finite element analysis (FEA). For this prototype
we concluded that use of FEA was not necessary because we did a static analysis. Software packages such
as Rhino 3-D are capable of modeling and FEA analysis all in one, but require the technical skill and
integral knowledge of the program to fully utilize it. We did not have this skill at our disposal, else would
have opted to compile all of the described steps.
Another advancement of this project would be to run the motion analysis on both the base line and
prototype shoes. The motion analysis would provide a real time comparison of changes in gait pattern.
Though the static analysis used the biomechanics hardware/software and the motion sensing equipment, we
ran the experiment in order to extract the ground reaction forces and the lever arm shift within the knee.
Having the markers on the test subject in the static analysis allowed us to measure the lever arm which is
necessary to calculate the moment about the meniscus within the knee. To reiterate; dynamic analysis
would provide a deeper glimpse into the effects of the L.O.A.F.E.R shoe on gait.
Additional test subjects would be ideal for a number of reasons. Foremost is being able to average a larger
pool of data for comparison between baseline measurements and prototype measurements. But one area
that we did not explore in great detail was user comfort. The tests were conducted on one of the group
members, and were tried by the others: from the cumulative five were all satisfied with comfort and
aesthetics, but a proper marketing survey of the product is essential for any large scale production.
The densities of the two materials we used satisfied the design criteria in limiting the ground reaction forces
and internal moment, however the compression of the material on the heel strike will vary with body
weight, thereby manipulating the angle induced in the midsole. A way to compensate for this discrepancy
would to prototype another shoe with different materials that have proportionately scaled moduli of
elasticity. Therefore, a person whom weighed 280lb. could purchase a pair of shoes that would have, on
heel strike, the same angle (around five degrees) that a person of 180lb. experiences.
70
6 Works Cited
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[4] Hohmann, Erik., Wortler, Klaus., and Imhoff, Andreas. “MR Imaging of the Hip and Knee Before and
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[7] Kerrigan, Karvosky, Lelas, Riley. “Men’s Shoe and Knee Joint Relevant to the Development and
Progression of Knee Osteoarthritis.” The journal of Rheumatology 30.3 (2003): 529-533.
[8] Crenshaw, Stephanie J., Pollo, Fabian E., and Calton, Ericka F. “Effects of Lateral-Wedged Insoles on
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[11] Turner, Jerome A. “Shoe Incorporating Improved Shock Absorption and Stabilizing Elements.” US
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[12] Toda, Yoshitaka. “Device and Method for Treating Arthritis of Knee.” US Patent 6585674. 1 Jul.
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[13] Kerrigan, D. Casey. “Joint Protective Shoe Design.” US Patent Number 6725578. 2004
[14] Benno, M. Nigg, and Morlock, M. “The Influence of Lateral Heel Flare of Running Shoes on
Pronation and Impact Forces.” Medicine and Science in Sports and Exercise. Vol 19, No 1 (1986):
294-302
[15] Kakihana, Akai, Nakazawa, Takashima, Naito, and Torii. “Effects of Laterally Wedged Insoles on
Knee and Subtalar Joint Movements.” Arch Phys Med Rehabil. Vol 86 (2005): 1465-1471.
[16] Bobbert, Maarten. Calculation of Verticle Ground Reaction Force Estimates During running from
Positional Data. J.Biomechanices Vol. 24, pg 1095-1105. London
[17] Winter, David A. Biomechanics and Motor Control of Human Movement. John Wiley & Sons, Inc.
2005.
“Knee OA Progression” Ferring Pharmaceuticals. © 2005-2006. 13 September 2006.
http://www.euflexxa.com/about.oa/progression.aspx.
“Total Knee Replacement” Ortho-MD.com. April 14, 2006. 13 September 2006. http://www.orthomd.com/totalknee.com.
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8 Appendix A – CAD Renderings Size 11
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74
75