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.

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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).

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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

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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

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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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