Ergonomic Sacroiliac Joint Relief Cushion Final Report

Ergonomic Sacroiliac Joint Relief Cushion Introduction to Engineering: Design Practicum 170: Lab 309 Date: 05/02/19 Client: Dr. Shwetha Simhan, Pain Health and Wellness Institute Team Members: Stephanie Brink, Adeline Drier, Benjamin Haas, Alexander Muhl, Rashelle Pershman, Benjamin Sevart, Brinda Shivapuja, Galvin Wei, and Lindsey Weiss Instructor: Dr. Mitchell Tyler, Senior Lecturer in Biomedical Engineering SA: Maggie Freking, Student Assistant

Abstract There are many chairs on the market with curved seat backing that offer support for the spine and muscles. However, they fail to address a major, and often overlooked, cause of back pain: the Sacroiliac (SI) joint. A modifiable seat cushion was created to target back pain caused by stress on the SI joint. Dr. Shwetha Simhan, the client, is a doctor based in Milwaukee, WI. At her request, a seat cushion was created that can be attached to a traditional chair. Using an inflatable air bladder to create a bump located inside the cushion, much of the pressure was taken off of the SI joint and Ischial tuberosity when sitting. This reduces strain on the spine and lower muscles and in turn lowers back pain. The bump is adjustable to allow the user to place the bump in a spot that releases the strain on the SI joint.

Finally, there are two foam densities strategically layered to provide optimal comfort, as well as a proper release of tension on the joints. Overall, this design provides a comfortable, but slightly bulky solution to a large majority of those with lower back pain.

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Table of Contents Introduction Problem Statement

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Client Information

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Background Research

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Motivation

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Existing Technology

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Social/Global Impact

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Design Specifications

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Rejecting / ……………………………………………………………....

Accepting Methods

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Standards and Regulations

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Preliminary Designs

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Preliminary Design Evaluation

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Preliminary Final Design

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Free Body Diagram

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Methods Design Approach

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Fabrication Materials & Explanation

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Fabrication Methods

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Testing Plan

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Evaluation of Final Prototype

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Conclusions & Final Work

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References

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Acknowledgements

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A: Product Design Specifications

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B: California Technical Bulletin

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Final Prototype Testing

Appendices

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Introduction Problem Statement Back pain is a major public health concern with 50-75% of cases stemming from stress on the sacroiliac joint. Dr. Simhan has proposed a design for a new ergonomic desk chair with three unique components targeted to release muscle strains in the pectoralis minor and reduce tension on the sacroiliac joint. The chair is aimed for ages 3+ with a maximum load of 250lb in any setting where there is prolonged time in a chair [1]. The cost for chair and modifications should be around $100, and the new design must be safe, comfortable, and compact. The detachable seat must have an adjustable bump in front of the sacroiliac joint to reduce pressure and accommodate for different body sizes. This design differs from the common design variation of a fixed seat curvature that does not relieve pressure on the sacroiliac joint. There are no current ergonomic chairs on the market that reduce tension on the sacroiliac joint; however, there are other non-desk chair products and active methods that target these goals, including crossing your legs when sitting or active stretching.

Client Information Dr. Shwetha Simhan, MD is a doctor primarily located in Milwaukee, WI, with other offices in West Bend, WI and Madison, WI. She is a Pain Medicine specialist. Dr. Simhan is affiliated with the Pain Health and Wellness Institute [2].

Background Research To better understand the problems of current office chairs and the pain on the SI joint, lots of research went into ergonomic office chairs and the anatomy of the human pelvis. The images below show the anatomy of the pelvic region. Figure 2 demonstrates the positioning of the pelvis and spine with correct posture. Figure 3 points out the location of the SI joint and Ischial tuberosity.

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The sacroiliac joint is only supposed to move 2mm-4mm in any direction [5]. Lower back pain can be due to extra movement, pushing the spine down and Ischial tuberosity up [5], [6]. Of the population, 90% reports having lower back pain, with 10-25% caused by stress on the Sacroiliac joint [5]. A recline in the chair can reduce pressure on the sacroiliac joint by 40 percent [7]. Upon researching seat upholstery, it was found that the fabric needed to be nonflammable to meet the standards for materials on chairs [8], [9], [10].

Motivation Throughout her career, Dr. Simhan was approached by many patients suffering from back pain. Often, they undergo surgery that only partially relieves their pain. She has discovered that extended periods of sitting can put pressure on the Sacroiliac joint and spinal disks, leading to pain. Knowing this could be fixed without surgery or injections, Dr. Simhan decided to develop a chair seat that relieves pressure on the sacroiliac joint by placing a bump inside the cushion.

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Existing Technology SUNFICON Inflatable Comfort Cushion (See Figure 4) is equipped with 56 plump 3D air cells to provide support for the back and hip. It is adjustable so customers could pump to any inflation level best for them, reducing up to 30% of pressure from sitting. The price of this product is $34.99 [11].

Although there are countless models of ergonomic chairs and seats, including ones with air pumps [12], none use an adjustable seat bump to relieve pressure on the SI joint. Dr. Simhan has design that is currently patent pending showing the adjustable bump (Figure 5). The ergonomic chairs on the market unfortunately only accommodates for comfort of the position and shape of the body.

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Social/Global Impact Millions of people, including students and those with desk jobs, spend a large part of their day in a chair. While SI joint pain may not appear right away, it can be caused by the long term effects of sitting with improper body positioning. Many people resort to surgery and injections when the core of the problem is how they are sitting. The cushion aims to create a bump that takes tension off the SI joint and relieves this pain, preventing any unnecessary surgeries and injections. It is believed that this design could positively affect the affecting millions of people worldwide who suffer from back pain due to long-term sitting.

Design Specifications ● Performance requirements: the chair will be used to correct the sitting posture of people who suffer from back pain caused by SI joint stress or those at risk of the condition ● Dimensions: The seat modification must be suitable for a 22”x16” seat [13], and the bump should protrude up by 2” at the peak with a 2” gradual decline on each side ● Safety: the chair must be able to withstand the load of a person (up to 114 kg=250 lbs) [1] sitting on it for extended (~8 hour) periods of time, every day of the year.

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● Accuracy & Reliability: users should be able to replicate their desired seat bump heights, which requires consistency between the dial/lever/adjustment method position and actual chair height. Heights produced by the same adjustment position should vary by no more than 2mm (approx 4% of total height, assuming a 5 cm total height). ● Weight: the modification should weigh, in total, between 1.5-2.0 lbs.

Reference: ● Full PDS with more design specifications is located in Appendix A

Methods Design Approach Before the group started brainstorming ideas, many weeks were spent researching the problem. This research included the anatomy of the spine and pelvic region, as well as current methods on targeting SI joint pain. Multiple images were received from Dr. Simhan, and those images were used to build some ideas off of. After this research and discussion with the client, the group was able to decide the essential components needed for the design. First and foremost, it needed to be adjustable to suit all consumers and each person’s needs. Additionally, the bump must be functional in the middle third of the seat and raise a maximum 2 inches in height to ensure pressure release. As as group, the first step was formulating some ideas outside of class.

Once the group got together, each person explained how their design would work. No idea was shot down and anything was fair game. During this time, the group was also able to build and combine some of the designs to create new ideas.

Rejecting/Accepting Methods Once all the ideas were presented, the group started analyze them. The first criteria was if the design could be successfully created in the allotted time. This eliminated a few designs, like the “Jack” and “Lift” ideas. Next, a design matrix was used to rank each design with certain criteria. After the design matrix, the top ranked designs were The Egg, Detachable, and The Air Pump.

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Standards and Regulations Both legal standards, such as the California Technical Bulletin 117-201 [10], and voluntary industry standards, such as the Polyurethane Foam Association standards guide [8], govern the use of polyurethane foam. As a fire hazard, polyurethane used in home upholstery must be covered with flame-resistance material.

In addition, because the seat cushion is meant to alter the human posture while seated in order to prevent a medical issue (back pain), the seat cushion would be classified by the FDA as a Class I medical device. Since this device is only for proof-of-concept purposes, however, and is not going to consumers, the FDA regulations requiring registration do not apply to this prototype.

Preliminary Designs The Egg Design Summary This design aims to release SI joint by creating a “bump� that is manually turned with a lever. The design contains a base with rails, a carriage, firm egg shaped object, and a bump (Figure 6). The lever and egg shaped object are joined and move together. There is a smooth railing system that allows the carriage to slide back and forth effortlessly. To lock the carriage into place, there will be tightening screws that will forcibly push down on the carriage and hold it into place.

Advantages

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● There is low risk of breaking egg shaped object and bump while sitting down because of the material of these parts. ● Rail system would allow for easy movement.

Disadvantages ● The fabrication process is complicated. ● It would need to have a locking mechanism for lateral and vertical movement. ● The egg shaped object would not move smoothly with the lever.

The Detachable Summary This design was to have the device detachable so you could use it on any type of chair.

The bump would be built in the strap using an air bladder (Figure 7). The strap would enable customers to laterally adjust the bump. The bump would be secure using two side straps that would be secure around the bottom of the chair.

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Advantages ● It is very universal. ● It is easy transport. ● The fabrication is simple.

Disadvantages ● It has as lower comfort due to lack of cushioning. ● The range of adjustability allows for the ease of misuse and possible harm.

The Air Pump Summary The main idea of this design is that will be an air bladder placed on top of two dowels (Figure 8). The dowels will be placed on a wooden base with a railings on each side to move it laterally. These railings will be wave-like, allowing the dowels to rest in a certain position.

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Advantages ● The user can easily adjust the bump with the pump on the air bladder. ● The air bladder can withstand weights up to 500lbs ● The air bladder can be pumped up while in use.

Disadvantages ● The air bladder is not long enough to fit the length of the seat. ● The user must stand up to adjust the air bladder laterally.

Preliminary Design Evaluation Matrix A design matrix is a good way to evaluate different designs. 8 criteria were used for design purposes. As Figure 9 shows, safety is in first place with 20% of weight, because safety of the consumer always comes first. Adjustability, ease of use, comfort and cost are weighted with 15% each. Adjustability is very important because this seat should help people with different needs. The ease of use and comfort are both important for the consumer while the product is in use. Cost is ranked this way to ensure it is accessible to as many people as possible.

Reliability is given 10% because it is important for the product, but not immediately relevant to the consumer. Both universability and compactness are weighted 5%, because they have the least impact on the consumer and will not affect the usability of the product.

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Design Evaluation The Egg design was found to be the best for safety, as there are just mechanical parts.

Additionally, it was best for cost, as it did not require an air bladder, which could be quite expensive. It would, however, be quite bulky.

The detachable design received high scores for universality and compactness. As there is no bulky cushion, it is the smallest design, and the straps would allow it to be put on nearly any seat. For the same reason (lack of cushion), it did receive a low score on comfort.

The air pump received a high score for adjustability, but low scores on compactness and universality, for the same reasons as the Egg.

Preliminary Final Design In consultation with the client, it was decided to move forward with the air pump design and the Egg design. These two designs showed more promise, so the group moved forward with them. Unfortunately, as the semester progressed and prototypes were made, it was realized that the egg design was not feasible. There were a lot of issues that still needed to be addressed, which was realized with the help of a TEAMLab consultant. Because of this, the client was informed that the group will solely progress with the air pump design. To improve the design, some elements were added from The Detachable and Egg designs to the Final Design (Figure 10).

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Free Body Diagram Free body diagram is drawn to to analyze forces exerted on different parts of the prototype (Figure 11).

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Fabrication

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Fabrication Materials Explained Our client wanted the product to be comparable in price to other seat cushions. Upon further research, it was determined that this was between $50-$100. A wooden base and railing system were chosen because of its strength and durability.

Two different densities of foam were chosen, high (1 inch/44 lbs) and medium (1 inch/36 lbs) to build a comfortable yet solid cushion.

For our air bladder, the group looked into a custom bladder to extend the length of the sear, but received quotes upwards of $200-$300, which was far too expensive. It was decided to purchase a shorter air bladder from Amazon at a much cheaper price. The group also bought longer tubing.

One of the main elements favored by the client was a bean bag idea under the base to fit any chair. A “pillow” was created to fulfill this need.

Finally, to secure the seat to the chair, the team added buckles and straps to the cover.

There will be two buckles on each side to attach to the bottom of any chair.

Fabrication Methods Base Fabrication for the base required Solidworks and Vcarve files to be used with the Laguna CNC Router. It would be used to make to side pieces and the base (Figures 12 and 13). The wood used was plywood, about 0.685” thick. The Vcarve files were uploaded and connected to the router, which then properly carved the designs from the wood. A jigsaw was then used to round off the corners of the base to allow it to fit more chairs. Sanding and files were required to make the holes of the wave a little larger to prevent the dowels from getting stuck.

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Foam The foam design required a lot of trial and error. The group realized that to get the slope of the seat, it needed to be made in separate parts. The high density and low density foam was cut to create the slope and give the user the ability to move the bump/foam without compromising the the gradual incline or its general movement. The low density foam was placed in front of and behind the air bladder, providing some resistance of movement but also comfort.

Then high density foam was added between the air bladder and the system so the bump could extend the whole width of the seat.

The high density foam was cut to fit between the gaps in the dowels. The team placed 3 pieces of foam near the front of the base to create the gradual decline; the first and second were high density and fit the entire width and length of the base, and the third was low density for added comfort and decline. Two layers of high density foam were also added in the back for more comfort. Low density foam was put underneath the bladder to increase maximum height change. All of these pieces were stitched and assembled together (Figure 14).

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Dowels and Bladder Both the dowels and the air bladder were bought on Amazon. The bladder was attached on top of the dowels using standard duct tape (Figure 15). The handles for the dowels were made using the 3D printer at the Makerspace and glued into place on the dowels. Upon testing, it was determined that wooden dowels would not be stable enough, so steel dowels were bought, which were cut down to the correct length.

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Final Prototype The basis for final Air Pump design will be as follows and as seen in Figure 16. Resting on top of the dowels will be an air bladder. This bladder, when pumped, will inflate the bump within the seat. The air bladder and surrounding area will be covered in foam to provide comfort and support. Finally, all of this will be covered in fabric tailored to fit the material compactly and as one coherent seat. The final design was fairly easy to fabricate, but some changes to the foam had to be made to fit the size of everything inside of the fabric.

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Testing Testing Plan Conditions: Each person will use the same type of seat with the seat cushion that was created. The time spent sitting on the seat modification will be about 3-5 minutes. There will be at least 3 trials for each test protocol and will be rated by the user on a scale from 1-7 with 1 being poor and 7 being excellent.

Data will be recorded in a table and analyzed.

1. Chair Drop Functional Load [1] Description: ​A 225 lb weight is positioned 6 inches above the chair and allowed to free-fall onto the center of the seat. The chair passes if there is no structural breakage or loss of serviceability [1].

Justification: ​Our seat modification needs to withstand a large amount of direct weight.

Additionally, there can be no structural damage under large amounts of direct weight.

Analysis: ​A 225 pounds of weight was not found to drop on the chair, but one of our team members weighed 170 pounds. Using the equation for potential energy to find that dropping 170 pounds from 8 inches will give the same amount of energy as 225 pounds from 6 inches. Our team member sat down from 8 inches, and jump up twice to get above 8 inches for a total of three trials. For each one, no structural damage was seen, and the seat still functioned as designed.

2. Objective Vertical Adjustability Description: ​Fully inflate the bladder and measure the height from the bottom of the aluminum dowels to the top of the air bladder. Compare the difference between the two measurements to find the vertical change in height produced by the bump. Run five trials to produce an average.

Justification: ​The chair needs to be able to create a bump that will relieve the pressure on the sacroiliac joint that is present when the person is sitting on the chair.

Analysis: ​The average change in height was calculated to be 1.8625 inches, slightly under our goal of 2 inches (Figure 17), but does get above 2 inches with error bars. With these tests, it was found that a fairly good bump was created that will relieve the pressure. A custom air bladder would be needed to reach an average 2 inches in change in height.

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3. Ease of Adjustability Description: ​Have each group member adjust the seat cushion horizontally and rate the difficulty of doing so on a 7-point scale.

Justification: ​The consumer of the seat should not have many difficulties adjusting the position of the bump.

Analysis: ​According to the results in Figure 18, it was determined that the seat cushion was not adjustable enough, so a few changes were made to the shape of the foam, which were preventing easy movement.

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4. Comfort Level Description: ​Have each team member sit on the full prototype and rate the comfort and relief of the seat on a scale between 1-7. A rating of 4 would indicate the same comfort/relief as a normal office chair, less than 4 being worse, and more than 4 being better.

Justification: ​The seat needs to be as comfortable as possible.

Analysis: ​It was found that the average for the comfort was 4.9 and the relief was 5.4. Using error bars, these results show that our seat is statistically better for comfort and relief than a normal office chair (Figure 19).

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5. Number of Pumps Description: ​Fully deflate the air pump so no air is left in the bladder. Without any pressure on the bladder, fully inflate the air bladder, and count the number of pumps it takes to to fully inflate the bladder. Run five trials of this and take the average. Put 170 pounds of weight of the air bladder and repeat the same test five times and take the average.

Justification: ​The air bladder should be fairly easy to pump up even when a person is sitting on the bladder.

Analysis: ​Inflating the bladder while sitting on the cushion only requires 6 more pumps on average than inflating without sitting on it (Figure 20). Statistically there is not a difference between the pumps required to fully inflate between sitting on the cushion and not sitting on the cushion.

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Evaluation of Final Prototype 5 tests were done to evaluate how our prototype would perform, and if it would meet our standards. Our comfort test found that our seat was comfortable than an average chair, but still found some areas where comfort could be improved, which was solved by adding more foam in the back and on the sides. A bump that was 2 inches in height was also needed. A first round of informal testing was done and found the height of the bump was around 1.5 inches. To solve this, some foam was added underneath the bladder, making the bump height 1.8625 inches. In order to achieve the full two inches, a customized bladder would be needed. Our seat is safe to use and could easily support a large weight, even when dropped on it. In cutting down the base size and rounding its corners, the cushion is able to fit and be attached to most chairs (Figure 21). Our testing found that the seat is fairly easy to adjust and use, although it is large (Figure 22).

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Conclusions Back pain is major health concern that stems from sacroiliac joint pain. Most people resort to surgeries or injections for relief. However, our client, Dr. Simhan proposed a design that targets sacroiliac joint pain using a modification to an office chair cushion. This design would create a bump in the seat that relieves some of the pressure on the spine. Our proposed design is called the “Air Pump�, which includes an air bladder located inside of the cushion. It is used to create the necessary bump and can adjusted laterally. To add comfort and to create a gradual incline, foam was added all throughout the cushion. For next time, different materials would be used to make the design sturdier and more weight bearing. Also, the bladder idea would be refined and add a more suitable bladder that would extend the length of our seat. Overall, the design addresses the problem given by our client.

Future work To complete our prototype, the upholstery needs to be modified to fit our current base size and make it look more professional. A way to significantly improve our design would be to have a custom air bladder that spans the full length of the seat to have enough air space to lift the bladder up to 2 inches. If there was more time and money to get another prototype made, this would have been done.The custom bladder would have improved our design because the user would have then felt the bump more evenly throughout the seat.

Another way to improve our design would be to create a way to allow the user to move the bump laterally while sitting down. A mechanism was not found that would be able to sustain the force of a person while being adjusted without causing the user too much of a struggle.

Additionally, our prototype is made of wood, making our design heavier than desired. With more time and research, the group would be able to find a lighter material. Finally, an improvement would involve finding tubing for the air pump that would be shorter and more easily accessible for the user to grab.

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References [1] ​BIFMA International Chair Standards, B ​ IFMA. [Online]. Available https://www.lifetime.com/library/pdf/bifma.pdf. [Accessed: 03-Mar-2019].

[2] “Dr. Shwetha Simhan, MD - Reviews” Vitals, [Online]. Available: https://www.vitals.com/doctors/Dr_Shwetha_Simhan.html. [Accessed: 07-Mar-2019].

[3] S. McLaughlin, “Simple Steps to Eliminate SI pain,” Align Integration & Movement, 05-Mar-2013. [Online]. Available: https://www.alignforhealth.com/blog/simple-steps-to-eliminate-si-pain. [Accessed: 20-Feb-2019].

[4] R. Cole, “Practice Tips for the SI Joints,” Yoga Journal, 28-Aug-2007. [Online]. Available: https://www.yogajournal.com/teach/practice-tips-for-the-si-joints. [Accessed: 20-Feb-2019].

[5] M. Raj and M. Varacallo, Sacroiliac (SI) Joint Pain. Treasure Island, FL: StatPearls Publishing LLC, 2018.

[6] J. Muscolino, “What are the causes of sacroiliac joint dysfunction?,” Learn Muscles, 22-Dec-2017. [Online]. Available: https://learnmuscles.com/blog/2017/12/01/causes-sacroiliac-joint-dysfunction/. [Accessed: 20-Feb-2019].

[7] J. Stensland, Ergonomics of Sitting. [Online]. Available: http://ergo.human.cornell.edu/dea3250flipbook/dea3250notes/sitting.html. [Accessed: 20-Feb-2019].

[8] “FPF and Fire Safety,” Polyurethane Foam Association. [Online]. Available: https://naturalupholstery.com/2014/01/diy-upholstery-tips-cushion-foam-basics/. [Accessed: 28-Mar-2019].

[9] “Polyurethanes,” American Chemistry Council. [Online]. Available: https://polyurethane.americanchemistry.com/Flexible-Polyurethane-Foam/. [Accessed: 28-Mar-2019].

[10] ​State of California Department of Consumer Affairs, S ​ tate of California. Technical Bulletin 117-2013. Available: https://www.gsa.gov/cdnstatic/TB_117_2013.pdf. [Accessed: 28-Mar-2019].

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[11] “​SUNFICON Inflatable Comfort Cushion Air Chair Pad Portable Car Seat Office Chair

Wheelchair Cushion Anti Bedsore Pad Orthopedics Cushion Pain Pressure Relief Cushion Camping Seat Mat 18'' x 16'' Grey” Amazon, [Online]. Available: https://www.amazon.com/dp/B07MH6VJBC/ref=sspa_dk_detail_0?th=1. [Accessed: 18-Apr-2019].

[12] “Choosing a Cushion” AliMed, [Online]. Available: https://www.alimed.com/cushions/.

[Accessed: 18-Apr-2019].

[13] “DEA 3250/6510 CLASS NOTES, Sitting and Chair Design” Cornell University [Online].

Available: http://ergo.human.cornell.edu/dea3250flipbook/dea3250notes/sitting.html. [Accessed: 08-Feb-2019].

[14] “Is the Product a Medical Device?” U.S. Food & Drug Administration, 22-Mar-2019.

[Online]. Available: https://www.fda.gov/medicaldevices/deviceregulationandguidance/overview/classifyyourdevice/ ucm051512.htm. [Accessed: 28-Mar-2019].

[15] “What’s the Difference Between the FDA Medical Device Classes?” BMP Medical, 2-Feb-2018. [Online]. Available: https://www.bmpmedical.com/blog/whats-difference-fda-medical-device-classes-2/. [Accessed: 28-Mar-2019].

Acknowledgements Our group wishes to thank the following people for their support of this project: ● Dr. Shwetha Simhan ● Dr. Mitchell Tyler ● Dr. Tracy Puccinelli ● SA Maggie Freking ● TEAMLab Consultant Michael Hughes ● Makerspace Shop Manager Karl Williamson ● Quinn Sabin & all other Makerspace/TEAMLab staff

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Appendix A

Problem Design Specifications Title Ergonomic Muscle Release Chair Badger BMES: Stephanie Brink, Adeline Drier, Ben Haas, Alex Muhl, Rashelle Pershman, Ben Sevart, Brinda Shivapuja, Galvin Wei, Lindsey Weiss Function Back pain is a major public health concern with 50-75% of cases stemming from stress on the sacroiliac joint. Dr. Simhan has proposed a design for a new ergonomic desk chair with three unique components targeted to release muscle strains in the pectoralis minor and reduce tension on the sacroiliac joint. The chair is aimed for ages 3+ with a maximum load of 250lb in any setting where there is prolonged time in a chair. The cost for chair and modifications should be around $100, and the new design must be safe, comfortable, and compact. The detachable seat must have an adjustable bump in front of the sacroiliac joint to reduce pressure and accommodate for different body sizes. This design differs from the common design variation of a fixed seat curvature that does not relieve pressure on the sacroiliac joint. There are no current ergonomic chairs on the market that reduce tension on the sacroiliac joint; however, there are other non-desk chair products and active methods that target these goals. This includes crossing your legs when sitting or active stretching.

Client Requirements ● The seat modification must be capable of providing relief for the SI joint ● The adjustable bump must be around 2 inches with a 2 inch gradual decline on each side ● The user must be able to move the bump back and forth so it is approximately four inches from the knee. ● The adjustable bump must have a stopper, so you can only move it between the middle 3rd of the seat. ● The modification should not wobble on the chair seat when used.

Design Requirements

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Physical & Operational Characteristics a. Performance requirements: the chair will be used to correct the sitting posture of people who suffer from back pain caused by SI joint stress or those at risk of the condition. b. Dimensions: The seat modification must be suitable for a 22”x16” seat [12], and the bump should protrude up by 2” at the peak c. Weight: the modification should weigh, in total, between 1.5-2.0 lbs. d. Safety: the chair must be able to withstand the load of a person (up to 114 kg=250 lbs) [1] sitting on it for extended (~8 hour) periods of time, every day of the year. e. Accuracy & Reliability: users should be able to replicate their desired seat bump heights, which requires consistency between the dial/lever/adjustment method position and actual chair height. Heights produced by the same adjustment position should vary by no more than 2mm (approx 4% of total height, assuming a 5 cm total height). f. Life in Service: the seat modification should last 3-5 years of regular use. g. Shelf life: the seat modification must be affixed securely enough to prevent damage even up to 3-5 years of storage. Also, the seat modification should not alter the overall shape of the chair in such a way that significantly increases the storage space requirements per chair. h. Operating environment: the chair needs to operate in an indoor, dry environment, such as an office, school, or home setting, and should function properly in the normal range of indoor temperatures (~65F to ~80F).

Production Characteristics a. Quantity: a single prototype, intended as a model for later fabrication by a third party. b. Target product cost: low enough to be generally affordable for the population at large; it should be about $100. The client specifically said “the lower the better.” c. Materials: can be made from a pre existing chair; otherwise it is acceptable to use leather or polyester. Recycled materials are encouraged.

Miscellaneous a. Medical device definition: The FDA definition of a medical device is as follows: “an instrument, apparatus, implement, machine, contrivance, implant, in vitro reagent, or other similar or related article, including a component part, or accessory which is: recognized in the official National Formulary, or the United States Pharmacopoeia, or any supplement to them, intended for use in the diagnosis of

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disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease, in man or other animals, or intended to affect the structure or any function of the body of man or other animals, and which does not achieve its primary intended purposes through chemical action within or on the body of man or other animals and which does not achieve its primary intended purposes through chemical action within or on the body of man or other animals and which is not dependent upon being metabolized for the achievement of its primary intended purposes. The term “device” does not include software functions excluded pursuant to section 520(o) [13].”

The chair modification we are designing is labeled as a Class I Medical device: Its definitions is as follows: “A Class I medical device are those devices that have a low to moderate risk to the patient and/or user. Today, 47% of medical devices fall under this category and 95% of these are exempt from the regulatory process. If a device falls into a generic category of exempted Class I devices, a premarket notification application and FDA clearance is not required before marketing the device in the U.S. However, the manufacturer is required to register their establishment and list their generic product with FDA. Examples include enema kits, elastic bandages, manual stethoscopes, and bedpans. [14]” b. Testing: testing on clinical patients will not be allowed, given the legal, ethical, and logistical concerns relating to human subject research. We intend to have one of our group members sit in the chair for 3 hours and have the participant give a review on the chair, rating each of the modifications for comfort and ease of use on a five-point scale. c. Codes & Regulations: because our design uses polyurethane foam, which is a flammability hazard, we must comply with industry and regulatory standards, which include: i.

California Technical Bulletin 117-2013 [9], Appendix B ii. PFA (Polyurethane Foam Standards) guide [7] d. Patent & Intellectual Property: given that the patent for the idea already exists, the prototype design must accomplish the functions described in the patent. Additionally, the prototype design must incorporate some novel and non-obvious innovation; in other words, the device modifications cannot be something one could find in a store

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ready-for-use. Current methods to improve posture include ergonomic kneeling chairs, head rests, back brace supports, and removable seat pads. e. Competing designs: although there are countless models of ergonomic chairs available, none of them use an adjustable seat bump to help relieve pressure on the SI joint and relieve back pain. Ergonomic chairs often have a seat with fixed curvature on the sides, which does not accommodate for the comfort of the SI joint, but rather the shape of the body.

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Appendix B

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