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StretchPRO: A Leg Separation Apparatus
Senior Project - 4013
Department of Biomedical Engineering
Lawrence Technological University
Team members: Kevin Ritchey (LTU), Norah Hammad (LTU), Brendan O’Neil (UDM),
Arafat Abdulmalek (UDM), David Duron (UDM), Ashley Gwiazdon
(UDM), Austin Carlisle (UDM)
Advisor:Dr. Eric Meyer
Table of Contents
Abstract…………………………………………………………………………....2
Introduction………………………………………………………………….........2
Disease State Fundamentals……………………………………………………...3
Market Analysis and Stakeholders………………………………………………4
Details of Design Concept………………………………………………………...5
Methods……………………………………………………………………………8
Project Relevance and Broader Impact………………………………………...10
Timeline…………………………………………………………………………..11
Budget…………………………………………………………………………….11
References/Images……………………………………………………………….13
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Abstract
StretchPRO is a leg separation device designed by Lawrence Technological University
biomedical engineering students in collaboration with University of Detroit Mercy mechanical
engineering and nursing students for our senior design project. The goal of the project is to affect
the life of our client by designing a device that will solve one or more of his needs. Due to severe
spasticity in his legs and groin, our client is unable to separate his legs without the assistance of
two people and sometimes wakes up with his legs crossed. Therefore, there is a need for patients
who suffer from spasticity in their legs and groin need to be able to stretch and separate their legs
without assistance, in a safe and effective manner. The StretchPRO achieves separation of the
legs by way of a scissor jack that would normally be used to change one’s tire. Two locking leg
stabilizers attach to the separator by way of lift off hinges. Once both legs are locked and hooked
into the separator, the user begins to slowly turn the crank in order to open the jack, thus
separating the legs to his or her comfort level.
Introduction
Our client is a 46 year-old male suffering from various complications of Brown-Sequard
Syndrome, a very rare spinal cord affecting only one side of the spinal cord. The client’s Brown-
Sequard Syndrome first presented as a result of a partial spinal cord injury sustained in an
accident in which his motorcycle was struck by a drunk driver. The spinal cord injury caused
various secondary conditions, namely severe spasticity in his groin and legs. Spasticity is a
condition in which certain muscles are continuously contracted and is caused by traumatic brain
injury, spinal cord injury, cerebral palsy, muscular sclerosis, and many other conditions.
Our first meeting with the client took place on September 21st, 2016. Immediately, we
were summoned to help the client out of his car and toward a seated area near University of
Detroit Mercy’s engineering building. At this time, we learned that the client uses a cane to walk
shorter distances or a wheelchair or heavy, powered scooter to travel longer distances. Once we
reached our destination and got acquainted, we began to ask the client about his conditions and
how they came about. He informed us that he was hit by a drunk driver while riding a
motorcycle 23 years ago (1993). In the accident, he sustained a T10 spinal fracture and a partial
spinal cord injury (cord was not fully severed), leading to his diagnosis with Brown-Sequard
Syndrome. After the accident, the client underwent a variety of surgeries on many parts of his
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body including his back, legs, abdomen, and right arm. Being an extremely active athlete, our
client found it very difficult to adhere to the recovery instructions of his doctor and likely
induced improper healing due to overactivity.
Although the client suffers from a large variety of issues, including foot drop, hernia, and
ulnar pain, we feel as though his most pressing issue is his inability to separate his legs without
assistance. At the current time, the client requires two people to grab each of his legs and
physically pull them apart as a result of his spasticity. The client often wakes up with his legs
crossed or locked in the fetal position. To combat this and other problems, he currently attends
physical therapy three times per week and receives therapeutic massage three times per week. He
has also been prescribed muscle relaxants but they were ineffective.
The most common method of treatment for spasticity is the use of muscle relaxants.
These drugs, such as Baclofen, Tizanidine, and Dantrolene, can be very expensive, ranging in
cost from $120 to $4800 annually - and, as previously stated, the client had no success with these
treatments. Other possible options for this condition include leg stretch machines (Fig. 1) and leg
separator pillows (Fig. 2) . Leg stretch machines, more commonly used in flexibility training for
gymnasts and martial artists, can be quite heavy (50-75 lbs.), expensive ($175-$450), and cannot
be used by our client because of how close together his legs are in their initial position. Leg
pillows, while cheap and lightweight, are also much too wide to fit between our client’s legs.
Figure 1 - Leg Stretch Machine by Valor Athletics Figure 2 - Cushion Knee Spacer - Nova Medical
Disease State Fundamentals
The patient’s presenting clinical issue was Brown Sequard’s Syndrome; a rare disease
which entails a partial spinal cord injury on only one side of the cord. Spasticity occurs often in
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conditions where the brain and/or spinal cord are damaged or fail to develop, such as cerebral
palsy, multiple sclerosis, spinal cord injury, and stroke. Essentially, spasticity results from the
loss of inhibition of motor neurons. This change in input to bodily structures tends to favor
excitation and therefore increase nerve excitability. CNS damage also causes nerve cell
membranes to rest in a more depolarized state. The combination of decreased inhibition and an
increased depolarized state of cell membranes, decreases action potential threshold for nerve
signal conduction, and thus increases activity of structures innervated by the affected nerves
(spasticity). The progression of spasticity depends heavily on the underlying disease it results
from. Most patients will see improvement with the use of physical therapy or medications.
Brown-Sequard Syndrome actually has a good prognosis for regaining of motor control, but most
of this improvement is seen within the first two years after the injury.
Market Analysis and Stakeholders
Spasticity affects more than an estimated 12 million people worldwide. Two of the most
common causes of spasticity are cerebral palsy and muscular sclerosis. In fact, about 80%
(400,00) of the approximately 500,000 cerebral palsy patients in the United States suffer from
some form of spasticity, as do about 80% (320,000) of the 400,000 country’s M.S. patients. If
even half of these 720,000 people (360,000) required some sort of device to separate their legs
(at an average cost of $312 per machine), this would amount to approximately $112,500,000 in
total.
The primary stakeholders for this device are the patients who cannot separate their legs
without assistance. They have a vested interest in being able to accomplish this very basic task
and would likely be purchasing the device for themselves unless it became classified as a
medical device. In this case, insurance companies would become major stakeholders. These
companies are going to want to put their money up for products that will be effective and reliable
so as not to require multiple purchases. Caregivers also hold a stake in this situation, as the
StretchPRO will eliminate one or more of their tasks by creating independence and mobility for
the patient.
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Details of Design Concept
We began our design process by coming up with different ways to separate the legs based
on existing products and methods. It was essential to us that our product provide independence,
is lightweight and/or portable, effectively separates the legs, fits between our patient’s legs, is
ergonomic, is relatively easy to manufacture, and accomplishes the desired task safely. In
addition, a later interview with the client revealed his desire to sleep in locking leg braces in
order to treat his condition while he sleeps. With that in mind, we came up with three initial
design concepts whose working titles were “the crank”, “the airbag”, and “the cords”.
The crank design (Figure 3) is based on existing leg stretch machines wherein the user
turns a crank-wheel which, in turn, separates the legs. This design differed from its inspiration by
its lack of a seat and heavy leg rests (for portability) and different separation mechanism
(although undetermined at the time). Our second design (Figure 4) was a pair of cords that the
patient would strap to his ankles and use to pull manually his legs apart. We considered this
design because of its extreme level of portability and its ability to provide independence, but
quickly determined that this design would be difficult to make ergonomic and would depend
heavily on the client’s strength level. The airbag concept (Figure 5) consists of two leg braces
attached to a centrally located air bladder that could be inflated with a standard mattress pump.
This design’s ability to minimize its width would allow it to be placed between the client’s legs
with little to no difficulty. Although the design would be very lightweight and portable and
provide independence, we were concerned that the patient would lack control of the separation
unless we made alterations to the pump, and making the leg braces detachable would be very
challenging.
5
Figure 3 - The crank Figure 4 - The cords
Figure 5 - The airbag
After many discussions among the group and with the client, we decided to move
forward with an improved version of the crank design; the StretchPRO (Figures 6, 7, and 8). The
StretchPRO consists of three main components; the separator and two leg stabilizers. The
separator is made up of a scissor jack (for changing tires) and two steel plates, each with the
female leaf of a lift-off hinge welded on. We decided that the jack should be situated above the
patient’s legs as opposed to between them in order to insure that the device fit comfortably
between the legs, hence the use of the tapering plates. Although aluminum was briefly
considered for the plate material, we eventually decided that steel would be the better choice due
its strength as well as the complexity of welding aluminum to steel (which the jack’s frame is
made out of).
6
Figure 6 Figure 7 Figure 8
The leg stabilizers, which were chosen for their ability to comfortably lock the leg in
place, attach and detach from the separator via the lift-off hinges, the male ends of which are
mounted on the stabilizers. The option to detach the the leg stabilizers was built in at the request
of the patient, and also allows for easier use of the device, as he can strap each leg individually,
avoiding awkward maneuvering of the fully assembled product. The patient straps both padded
leg stabilizers on, then attaches them to the stabilizer using the hinges. Aside from providing a
means of attachment and detachment, the hinges also serve to provide a second axis of motion
for each leg (Figures 9 and 10).
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Figure 9 Figure 10
Once the patient’s legs are strapped in and the immobilizers are attached to the separator,
the patient can begin to slowly turn the crank wheel to his desired level of comfort and
separation. The crank mechanism essentially elongates the jack’s existing screw and translates
the rotational motion of the crank 90 degrees in order to separate the jack using bevel gears
(Figure 11).
Figure 11
Methods:
Our first test will be a measurement of the force required to separate the patient’s legs via
force transducer luggage scales (Figure 12). To perform this test, we will attach the luggage
scales to each of the patient’s ankles and physically separate them as he normally does. We will
also do a static analysis of the system, taking into account the force the jack is exerting on the
legs due to the torque applied by the crank, as well as how much force the client will have to
apply to the crank in order to open the jack. By altering the length of the crank arm and the gear
ratio, we can presumably end up with safe, effective, and user-friendly device. In addition to the
aforementioned tests, we will also conduct basic user tests with the client to see how effective
the device is in separating the legs and to obtain feedback on issues such as comfort, weight, and
8
aesthetics. Of course, in order to perform these tests, we will need to get approval from
Lawrence Tech’s Institutional Review Board (IRB). Our team is currently working on our
application and finalizing our informed consent to be signed by our subject. We hope to be
approved by early January 2017.
Figure 12
Because we are going to be using a mix of custom fabricated and off-the-shelf
components for this device, we will be needing a variety of different pieces of equipment for its
production. The steel plates we will be ordering will not be the size or shape that they need to be
for our product, so we will need to cut them with either a metal-cutting band saw or a jigsaw. In
order to achieve the tapered shape that we need, we will need to outsource the fabrication of a
form made to our specifications. The form will be placed under the metal plate and a hydraulic
press will exert downward force onto the plate, bending it into the desired shape, as shown in
Figure 13.
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Figure 13
The metal plates will be welded to the jack, creating a steel on steel interface. The female
leaves of the lift-off hinges will be joined to the plates by brazing, a form of welding that, instead
of melting the base materials together, uses a melted filler metal to make the bond. This process
is better suited for thin components (the hinge plates are less than 1/10 of an inch thick) as it uses
much lower temperatures than welding, minimizing the risk of warping or burn-through.The
male ends of the lift-off hinges will be attached to the cloth leg stabilizers by way of simple
button fasteners. All welding will be outsourced.
Moving forward, we intend to address some of our current concerns including a potential
pinch hazard from the scissor jack as well as manufacturing and prototyping costs. To mitigate
the chances of a pinch occurring, we intend to design some sort of case or guard to block the
patient’s skin from any area on the separator that may cause an issue. As far as the
manufacturing costs, we are currently exploring our options with local welding shops to find the
best pricing in addition to looking for a manufacturer for the form we will need to bend our
plates. We will likely use 3D printed plastic plates in our first prototype which we are able to
print on campus.
Project Relevance and Broader Impact
The StretchPRO device will allow our client to do something that most of us take for
granted on a daily basis: separate his legs independently. Because his stance is so narrow, our
client has difficulty walking in his current state and often does not have people to help him
stretch his legs. This is especially detrimental to his ability to participate in many activities with
his young daughter, as well as his ability to enjoy the athletic activities that he once loved, such
as golf, tennis, and basketball. Being 46 years old now, the client has spent the last half of his life
living with the issues associated with his accident. Can you imagine spending half of your life
unable to do the things you love?
Looking at the bigger picture, this device could potentially help so many more people
than the single person that inspired it. The leg stretching machines that are currently on the
market are being used by gymnasts and martial artists to increase their flexibility, so there’s no
10
reason why our device could not be used in the same manner. Our device, however, would be
much more portable and usable for a wider range of customers. Also, other sufferers of leg and
groin spasticity would likely be able to benefit from this machine, especially if they are
encountering some of the same issues as our client (initial space between legs is too narrow to fit
existing products, muscle relaxants not working). For these reasons, we will be investigating the
steps the necessary to secure our intellectual property along with our UDM legal consultant.
Timeline
Budget
Based on the $1000 afforded to us by University of Detroit Mercy, we have assembled a basic
budget for the components which is as follows: (Note: We are still in the process of determining
the appropriate gears and crank arm length for the device so we have not priced these parts out
yet. We do estimate the bevel gear set to cost about $15. As far as the fabrication elements of the
budget, our research leads us to believe that the welding portion would cost around $50 per hour
and would only take one hour and are also in the process of acquiring quotes for the form needed
to bend the steel plates.)
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Item Cost Reasons
Ram Scissor Jack
$24.95
+ $11.26 shipping =
$36.21
- Lightweight (12 lbs.)
- 2500 lbs capacity
- 18-¾” lift (separation)
Ossur Knee
Immobilizers
$54.56 x 2
+ $6.55 sales tax =
$115.67
- Fully adjustable
- Provides immobilization in extended position
- Comfortable
3/16” A36 Steel
Plates
$15.34 x 2
+ $15.74 shipping =
$46.40
- Lightweight (7.66 lbs/each)
- 36,,000 psi yield strength
- Easy to weld, cut, form, and machine
Batallion Lift-off
Hinges
$7.59 x 2
+ $5.00 shipping =
$20.18
- 270 degree ROM
- Full surface mounting
- 88 lb load capacity
- 304 stainless
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