Schlewitz 1

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. Schlewitz 2

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. Schlewitz 3

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 Figure 1: Bunion on a patient prior to removal surgery. surgery Once common cause for MPE is post-operative weight bearing because, even though patients are Figure 2: Radiograph showing a raised first toe

1 www.cdc.gov/nchswww/data/ad300.pdf 2 Interview with Dr. Glaser Schlewitz 4 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 Figure 3: Closing wedge osteotomy with cut shown 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 for the product were discussed and Dr. Glaser reported he could handle those ends of the

3 http://www.doctormathews.com/bunion.html Schlewitz 5 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 to the doctors and there is no current way to stop MPE in the OR. The arch support Schlewitz 6 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 Figure 4: Melting high-density polyethylene considerations in the choice were ease of plastic pressing, buffing, strength, and economics. Dr. Jon Feulner at Sole Supports is an expert

4 Meeting with Dr. Whittaker 5 http://www.interpod.com.au/WindlassMechansimandFootOrthoses.htm Schlewitz 7 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 Figure 5: Geared motors from SDP-SI moment arm driving the CPM. The variable 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 Figure 6: Hubs selected for prototype deveolpment 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, Schlewitz 8 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:

Figure 7: BIOSS prototype showing arch support Schlewitz 9

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 Figure 8: BIOSS prototype showing motor attachment custom arch support. The 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 Schlewitz 10 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 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. Schlewitz 11

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. Figure 9: Current CPM device available from Patent numbers 5,297,540, 5,094,226, and Jace Systems 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

6 www.uspto.gov 7 www.jacesystems.com Schlewitz 12 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 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 Total Bunion and Production Costs: production line and toes deformities Parts and Materials operations: = $30-$40 labor costs were estimated at $35-$40. Parts for 304,000 (NIH Labor = $35-$40 1996) the device including plastic, hub, screws, washers, and plaster were estimated at $35-$40 Total BIOSS Projected Price: Applicable $250-$1000 as well. The major material cost was the motor procedures: Cost/Benefit ratio: 30,400 = $250/$800= .31 since it will cost around $20 per product. The Total Customers Net Yearly Profit with market share: (minimized): potential sales price was estimated anywhere 3,040 $350 - $80 = $250 Cost of MPE (per unit) from $250 to $1000. This was partially based on repair surgery = X 3,040 (people) $500-$800, extra the cost of repairing MPE was found by asking visits = $200-$400 =$ 760K Table 1: Economic analysis for BIOSS 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 Schlewitz 13 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 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 Schlewitz 14 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 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 Schlewitz 15 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:

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 Bud July 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 Schlewitz 16 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 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 Schlewitz 17

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 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.