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Inter-Operative Biomechanical Surgical Splint

Vanderbilt University

Department of Biomedical Engineering

Senior Design Course

By: Nick Schlewitz

Advisors:

Dr. Paul King; Vanderbilt University

Dr. Edward Glaser; CEO Sole Supports Inc.

Jared Cobb; Head of Engineering and CFO Sole Supports Inc.

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Abstract:

Every year over 300,000 bunion and other toe deformities are corrected by

surgical techniques and a majority of these operations carry a potentially crippling

complication called Metatarsus Primus Elevatus. There is currently no product or

method developed to combat this dangerous complication so many effective types of

bunion surgery are being abandoned. In response to this, a product is being developed to

stop Metatarsus Primus Eleavtus from occurring that has been named BIOSS. BIOSS is

a splint that is applied to a patient’s foot after bunion surgery that stops Metatarsus

Primus Elevatus from occurring using two different and effective mechanisms. The

project to develop BIOSS was funded and initiated by Dr. Edward Glaser and production

took place at Dr. Glaser’s business, Sole Supports Inc., located in Lyles, TN.

Background research was done and local podiatrists were questioned during the

development process to assess the problem and develop possible solutions. Once

production of BIOSS had begun, many obstacles were overcome which included material

selection, material placement, customizing the device, and many others. In the end, a

prototype for BIOSS was successfully produced and passed initial inspections by a

number of physicians. An economic analysis was performed and showed great profits for

producing such a device. While the prototype is working and meets the design

specifications, many steps still need to be taken to bring the product to the marketplace.

Some things left to be done are the development of sterilization techniques, insurance

authorization, and testing on actual patients.

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Introduction:

Every year hundreds of thousands of bunion removal surgeries are performed and

all carry the same risk of a potentially crippling complication called Metatarsus Primus

Elevatus (MPE)1. MPE is a common complication in which the big toe becomes

elevated above the smaller toes and becomes fixated in this uncomfortable position. This

condition poses not only a cosmetic distaste but can affect the persons gait cycle and

make walking next to impossible. The condition is so common that it is causing

podiatrists to seek an alternative, and sometimes much less effective, treatment for major

bunion deformity.2 The project at hand, the Interoperative BIO-mechanical Surgical

Splint (BIOSS), is designed to alleviate MPE following major bunion surgery using two

different and effective methods.

Before discussing the way MPE is to be fixed, an understanding of how it is

caused is necessary. A bunion is a calcium deposit which usually

forms at the heard of the first metatarsal. This deposit grows and

ends up pushing the big toe towards the other toes until surgery is

required to correct it (Figure 1). The bunion surgery complication

MPE can be seen by observing Figure 2. The first toe can become

fixed in this position by one of two ways following a bunion

removal surgery. Once common cause for MPE is post-operative weight bearing 1 www.cdc.gov/nchswww/data/ad300.pdf2 Interview with Dr. Glaser

Figure 1: Bunion on a patient prior to surgery

Figure 2: Radiograph showing a raised first toe

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because, even though patients are instructed not to walk on the foot, they don’t listen to

their doctor and put pressure on the healing toe, causing it to elevate. The second cause

for MPE is surgical technique. This is only a major issue when a closing wedge

osteotomy is

performed in

which the

head of the

first

metatarsal is

cut and

realigned. The closing wedge osteotomy, shown in Figure 33, has a cut made on the first

metatarsal which varies from surgeon to surgeon. The orientation and placement of this

cut plays a factor in the potential for MPE occurring. Currently, there is no template for a

precise cut that has been identified as an effective way to prevent MPE (Appendix 1).

These two separate causes for MPE are so common that they are preventing surgeons

from even performing closing wedge osteotomies.

The goal of this project is to develop a custom post-surgical splint that will

prevent the onset of MPE in patients recovering from bunion removal surgeries in an

economical fashion. As proposed by Dr. Glaser, the most effective way to do this is to

address the foot in the healing stages by applying a splint that provides both a custom

arch support and applies continuous passive motion to the healing big toe. The splint

must be capable of being produced at Sole Supports using their current facilities and

financial means. Pre-authorization by insurance companies and sterilization techniques

3 http://www.doctormathews.com/bunion.html

Figure 3: Closing wedge osteotomy with cut shown

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for the product were discussed and Dr. Glaser reported he could handle those ends of the

development. Finally, the splint must pass inspection by practicing physicians that will

potentially use the device.

Methodology

Before production of such a device could ensue, an extensive background

research on bunions, bunionectomies, and MPE was launched. Once bunions were

understood and the different types of bunionectomies were examined through literature,

contacts were made in the podiatric field. The first podiatrist contacted was Dr. Bud

Hawthorn at Summit Medical Center in Nashville, TN. Dr. Hawthorn owns a share of

Sole Supports Inc. and was willing to assist in development and potentially try BIOSS on

one of his patients. To help me understand what is involved in a bunionectomy, Dr.

Hawthorn invited me to observe a closing wedge osteotomy in the operating room. The

entire operation was documented in Appendix 1. By showing how the cut is made and

the current bandaging techniques used in current procedures, a better understanding of

the problem and possible solutions was attained. A meeting with Dr. Michelle Whitaker

at Centennial Medical Center in Nashville, TN confirmed the necessity of using such a

device to prevent MPE since it was a problem that she has seen before. The Innovative

Workbench software was executed on the device to help brainstorm potential solutions to

the MPE problem.

After the extensive background work that was done, it was clear why Dr. Glaser

wanted to construct BIOSS with the features discussed. The IWB software results (found

at http://www.bme.vanderbilt.edu/srdesign/2003/group1/) helped to understand that the

best way to attack MPE is during the healing stages since patients already doesn’t listen

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to the doctors and there is no current way to stop MPE in the OR. The arch support

would work to prevent MPE by initiating the windlass effect4. The windlass effect is

described as a reflex where the plantar fascia ligament pulls the head of the big toe down

when pressure is applied to it.5 With a constant arch support applied to the healing foot,

the big toe will be continuously pulled downward and thus eliminating the possibility of

MPE. The continuous passive motion of the big toe will work to improve healing

conditions as well as prevent MPE. By keeping the big toe in passive motion, blood and

essential nutrients will be circulated to the areas affected during the operation which

increases healing time and patient satisfaction. Also, the motion of the toe will prevent

adhesions in which the healing tissue or bones stick to each other causing a limited range

of motion or MPE. With those affirmations and considerations, a prototype was sketched

and production considerations were assessed.

The final design specifications were centered on those specifications deemed most

important. The arch support and CPM

device were to be incorporated so as to

cause little or no discomfort for the

patient or doctor. Each component was

individually considered and tested to

ensure that it was the correct choice.

The first consideration for

developing a prototype was the material

used for the foot bed. The main considerations in the choice were ease of pressing,

4 Meeting with Dr. Whittaker5 http://www.interpod.com.au/WindlassMechansimandFootOrthoses.htm

Figure 4: Melting high-density polyethylene plastic

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buffing, strength, and economics. Dr. Jon Feulner at Sole Supports is an expert on

plastics for the Sole Supports arch supports and assisted in plastic selection. As seen in

Figure 4, a high-density polyethylene plastic was one of the first considered. Re-heating

was necessary with heat guns since the presses left bubbles in the foot bed. This plastic

was initially chosen for its economic value and strength. After working with it, it was

decided that high-density polyethylene lost its strength after pressing and was difficult to

both buff and form.

The next consideration was that of the motor to drive the toe for the CPM

component. Dr. Robert Galloway at Vanderbilt University was consulted and many types

of motors were discussed. Since it is easier to have a fast motor than a slow one, a geared

motor was selected because the gearing allowed the motor to substitute speed for

strength. A

geared motor

(Figure 5)

was selected

from SDP-SI

for testing. The circular hub (Figure 6) was chosen to go around the shaft of the motor

so that

multiple

holes could

be drilled

into it to allow for a variable length of moment arm driving the CPM. The variable

Figure 5: Geared motors from SDP-SI

Figure 6: Hubs selected for prototype deveolpment

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length moment arm is crucial since the custom product will have to be adjustable to meet

the range of motion needs of the individual patient.

The mold used for pressing was created using the already in place custom plaster

casting method at Sole Supports. Using a foam casting box, the patient’s foot is pressed

into the foam and that box is sent to Sole Supports. Upon arrival, the foam foot is filled

with plaster and the plaster positive is polished. Then the plastic is vacuum pressed over

the plaster positive. This manufacturing technique was carried onto BIOSS by simply

adding extra plaster to the front of the foot in the foam impression stage. The extra

plaster allowed for a toe guard to be put onto the front of the device for protective

purposes.

With a manufacturing technique and a good idea of what parts would cost, an

economic evaluation was performed. Patent searches on existing devices were performed

to check competition and safety issues concerning the device were addressed. Finally,

authorization was granted by Dr. Hawthorn to bring him a finished product to use as a

test on a future patient.

Results:

A completed prototype was produced and is

shown in Figures 7 and 8. The final prototype was

made out of a polypropylene plastic as suggested by

Dr. Feulner. The plastic was selected based on its

low cost and its ability to be easily formed and

buffed. By observation of Figure 7, the arrow

indicates the position of the custom arch support. The

Figure 7: BIOSS prototype showing arch support

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positioning of the arch was directly correlated to my foot and was effective in promoting

the windlass effect. The plastic toe guard can also

be seen and this prevents the patient from injuring

the toe as it is healing. For normal operation, the

big toe is secured with a wide Velcro strap to the

toe guard while the other toes are fixed to the foot

bed. Observation of Figure 8 clearly shows the

motor used to drive the CPM component of BIOSS. The motor selected was a 3 rpm

geared motor with a 16 oz-inch torque from SDP-SI for $20. These specifications were

chosen since the speed was adequate to move the toe without discomfort while the torque

wasn’t high enough to injure the toe. The hub shown in Figure 6 was connected to the

shaft of the motor and the wire connecting the hub to the toe guard was made adjustable.

Locking nuts and washers were used to connect the toe guard to the foot bed with careful

attention being made in order to put the actual joint placement where the hole was drilled.

This was very important since the toe is supposed to be passively moving as in normal

walking and misplacing the pivot of the joint would cause abnormal healing to occur.

The placement of the motor took much consideration. Previous designs had attached the

motor near the heel with a long wire running along the side of the foot. The decision to

place the motor above the patient’s foot was very well accepted since it decreased the

length of the arm driving the toe and it made the entire device more compact.

The final considerations involved with the development of the prototype consisted

of a way to get power to the motor and the best way to attach the motor to the toe guard

to get the desired motion. It was theorized that a battery pack could be attached via long

Figure 8: BIOSS prototype showing motor attachment

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wires to the device. This battery pack, consisting of 6 Volts of potential difference,

would have an on/off switch and could be attached to a belt or pocket for easy patient

operation. The loaded device was measured to draw less than 1 mA of current so there

would be little need for any concern of batteries running out if fresh batteries were used

when the device was first turned on. There were many ways considered to attach the hub

to the toe guard, but a bendable z-wire ended up being the most effective choice. The

wire was designed to have multiple bends in it so that the practicing physician could

adjust its length so as to allow a desired range of motion. Another reason that a bendable

wire was chosen was for safety purposes. A safety analysis for the device was done

using the Design Safe software (the results from this program can be found at

http://www.bme.vanderbilt.edu/srdesign/2003/group1/ ). The major discovery found

from using this software was the need to address potential injury to the patients toe.

Since the continuously moving motor could either trap or over extend the big toe, the

wire was used as the breaking point. Since the wire would bend with increased pressure,

the big toe of the user would not be harmed and the wire would simply have to be

repositioned after the excessive load. With all of these specifications included, a final

prototype was assembled and presented to Dr. Glaser and Dr. Hawthorn.

Economic viability was a very important part in the development process. If there

was no need for the product or no profit could be made from mass production, all efforts

would be lost. Many factors were considered in determining the potential profits

including competition, market size, production cost, marketing capability, and cost to

benefit ratio. The competition analysis consisted of patent searches and web searches.

Many CPM devices were found but none were found to be custom for a patient. Patent

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numbers 5,297,540, 5,094,226, and 5,702,354 were all found to be CPM devices for a

toe.6 The only patented CPM in production was found to be #5,297,540 and this device is

available from Jace Systems and is shown in Figure 9.7 As can be seen from the picture,

there is no arch support and this device is not

mobile. Of all the podiatrists that were

contacted, none reported ever using a CPM

like the one from Jace Systems. This was

because of the high cost, due to physical

therapists and patient training that is involved,

the fact that the equipment must be rented, and

it is difficult for the patients to use at home. With little to no initial competition for

BIOSS, a market analysis was performed. The most recent surgical data was found for

1996 when a reported 304,000 bunion and other toe deformity operations were

performed.1 It was estimated by Dr. Glaser that 10% of these operations could benefit

from the use of BIOSS, leaving the number of potential customers at 30,400 patients per

year. With a potential 10% market share, BIOSS could very likely be sent out to 3,040

people per year. Marketing considerations were considered but easily solved. Sole

Supports is a growing company that does so with no commercial advertising. The way in

which BIOSS would be marketed would begin with Sole Supports current podiatric

clientele. Dr. Glaser currently travels the world speaking to podiatrists about Sole

Supports and he could very easily get the word out to these doctors that BIOSS is an

6 www.uspto.gov7 www.jacesystems.com

Figure 9: Current CPM device available from Jace Systems

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effective treatment for MPE. A cost analysis was performed and was found to be

exceptionally accurate due to the

existing labor force at Sole Supports. BIOSS production could be added to the current

production line and

labor costs were estimated at $35-$40. Parts for

the device including plastic, hub, screws,

washers, and plaster were estimated at $35-$40

as well. The major material cost was the motor

since it will cost around $20 per product. The

potential sales price was estimated anywhere

from $250 to $1000. This was partially based on

the cost of repairing MPE was found by asking

the manager at Dr. Hawthorn’s office. She

estimated a single toe repair to range from $500-$800 depending on the type procedure

performed. Adding in pre-op visits that range from $200-$400 brings the total cost range

from $700 to $1200. Of course, that’s without putting a dollar value on the extra pain,

suffering, possible lifelong limitations, and trauma of surgery which would raise the cost

of getting MPE to well over $2000. Clearly, the benefit of having BIOSS preventing

further operations goes well beyond the cost of purchasing it. The price is very flexible

and reasonable since, if the product is pre-approved by insurance companies as discussed

by Dr. Glaser, the patients insurance will pay for the device and the doctor will simply

reap the benefits and never see the cost. Net yearly profits (minimized from above

estimations) were estimated to be in excess of $750,000 per year. These calculations are

Total Bunion and toes deformities operations: 304,000 (NIH 1996)

Production Costs:Parts and Materials = $30-$40Labor = $35-$40

Total BIOSS Applicable procedures:30,400

Projected Price:$250-$1000Cost/Benefit ratio:= $250/$800= .31

Total Customers with market share:3,040Cost of MPE repair surgery =$500-$800, extra visits = $200-$400

Net Yearly Profit (minimized):$350 - $80 = $250 (per unit)X 3,040 (people)

=$ 760KTable 1: Economic analysis for BIOSS

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summarized in Table 1. This economic analysis shows that pursuing full scale

development and marketing for BIOSS is possible and potentially very profitable.

Conclusions:

The final working prototype was shown to both Dr. Glaser and Dr. Hawthorn.

Both doctors seemed very pleased with the product and were optimistic about its future

use. Dr. Hawthorn even said he would be willing to use a device resembling the final

prototype on one of his patients. The prototype successfully incorporated a custom foot

bed made from a low cost plastic that was easy to work with and strong. The arch was

incorporated into this foot bed and was successful at initiating the desired windlass effect.

A continuous passive motion device was added to the foot bed that effectively and safely

moved the toe with an adjustable range of motion. The costs involved in full scale

development were determined and have shown great promise for the future. A full

understanding of the complications involved with bunion surgery was attained and the

complication Metatarsus Primus Elevatus was understood in its entirety. A patent search

on current devices that alleviate symptoms of MPE was conducted and, thankfully, no

such device was discovered. It was found that BIOSS is a low cost product with little to

no competition, minimal startup costs, and a potentially huge market willing to pay for a

way to increase patient satisfaction. A few necessary steps are still necessary before

bringing the product to market, but a working device has been constructed.

Recommendations:

Continuing this project requires many additional steps in order to bring the

product to market. The first critical step is to file for a patent on the device in order to

ensure nobody makes a similar product before BIOSS comes to market. After a patent is

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written, extensive testing on the device needs to be performed. This should be done with

the Sole Supports staff and the device should be run for around 12 hours a day for 6-8

weeks, the normal healing time for bone. Any wear and tear occurring during this period

can then be recognized and fixed before a patient actually wears it. A very important step

that also needs to be taken is development of a sterilization technique. This is very

critical since the device will be in contact with an open wound and there is a very good

chance of infection if it is not properly sterilized. The battery pack has still not been

developed, but development should be simple and not take a whole lot of time. Pre-

authorization from insurance companies is an essential step that has yet to be taken.

Without approval from insurance, it is not likely that doctors or patients will pay for the

device. Following the critical steps listed above, a test study has to be organized and

executed. This would begin by working with Dr. Hawthorn to set up an appointment

with one of his patients. The patient would have to agree to use the device and all results

from that patients experience would have to be carefully documented. If successful,

multiple patients would then be acquired for study and local podiatrists would be

solicited to participate. The only ethical question concerning this device is whether or

not it will help patients recover more efficiently. If BIOSS is successful at improving

patient satisfaction and eliminating MPE, the results will sell themselves and any ethical

questions will be answered. Any doctor practicing without the use of BIOSS could

eventually be termed negligent if their patient developed MPE following an operation.

After all these steps have been taken, BIOSS will likely exceed expectations and become

synonymous with the bunionectomy.

References:

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1 www.cdc.gov/nchsww/data/ad300.pdf

2 June 28th , 2003, interview with Dr. Edward Glaser at Sole Supports Inc. Lyles, TN.

3 www.doctormathews.com/bunion.html

4 June 23rd, 2003, interview with Dr. Michelle Whittaker at Centennial Medical Center, Nashville, TN.

5 http://www.interpod.com.au/WindlassMechansimandFootOrthoses.html

6 www.uspto.gov

7 www.jacesystems.com

Appendix 1:

Trip to the OR with BudJuly 11, 2003

Dr. Bud Hawethorn was kind enough to allow us to watch him perform a closing

wedge osteotomy. We arrived at 7 and were dressing in scrubs and felt really important.

The patient was having a distal and closing wedge removal as well as having some

tendons cut. The foot was first dressed and sterilized before the plantarflexing tendon in

the heel was cut. Next the foot was cut open and some soft tissue was singed with an

electric shock. The first bone removal was at the metatarsal phalangeal joint and this was

a simple shaving off of the bunion and excessive bone at the joint. The toe was realigned

in the joint before the base wedge cut was executed.

Dr. Bud then moved to the base of the first metatarsal and cleared away more

tissue. He made two cuts in the bone which formed a V with a flat bottom. He explained

to us how the angle of the cut was the most critical element in preventing post-operative

complications. A vertical cut is necessary as opposed to angling the blade like writing

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with a pen to prevent elevatus. Bud then told this story about a man who was obsessed

with saran wrap. He decided to go see a psychologist to help him with his problem.

While checking in at the front desk, the receptionist looked up and said,”Clearly, I see

your nuts.” The bone was then realigned and two pins were placed to hold the bone in

place. The pins curled upward and were capped on the top. The patient was then stitched

up and put into a cast with a toe guard and rubber shock absorbers on the bottom. This

would prevent any pressure from being put onto the first met-head which could

jeopardize the operation.

Following the surgery, Bud sat down with us to discuss our project. He indicated

that 99% of elevatus was caused by surgical technique, where angling the blade at the cut

was the place of most importance. It would be difficult to incorporate a CPM to the toe

since it is fixed in the cast. He also indicated that closing wedge osteotomies are

diminishing in practice because of new operations that are less risky and more practical.

He has performed 6 or 8 of these operations so far this year and that is a common

number. He did not seem to think that our project was attacking a growing problem but

one that is diminishing.

August 4th Meeting with Bud

Today I went to Hermitage and met Dr. Hawthorn to ask about our project. The

main objective was to assure that moving the toe in the cast would be possible and if he

would be willing to try our product when finshed. Dr. Hawthorn said that he would be

willing to cast behind the toe and allow it to move. He also stated that he would be

willing to test our product if we brought him a design and it was sterile. He suggested we

use an X-ray to cook the device and sterilize it before packaging. He said that 60 degrees

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of dorsifexion and 20 degrees of plantarflexion would be sufficient movement ranges.

On a personal note, he stated that surgery practice is declining and that an external fixator

would be an efficient and popular way to move the toe. This information was noted and

relayed for further research. This meeting was very promising and gave us the necessary

information to move on with our project with these specifications in mind.