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​Designing an adjustable prosthetic socket using ReMake and Fusion 360

 
 

Who I am and what I do
My name is Claudine Humure and I am a rising senior at Wheaton College in Norton, MA majoring in biology and minoring in business and management. I have a great passion for prosthetic limb research and design as well as working with amputees of all kinds. I got into prosthetic design during the summer of 2015 when I interned with the Biomechatronics group at MIT Media Lab under the supervision of professor Hugh Herr and three of his graduate students. Before I got into prosthetic design, I did a number of clinical internships at different locations including Next Step Bionics and Prosthetics and Spaulding Rehabilitation Hospital.
 
This past summer, I worked as an intern at Autodesk. My internship project was about creating a prosthetic socket for above the knee amputees using ReMake and Fusion 360 as a way to use these tools to solve a social impact challenge. Social impact design is a branch of design that seeks to find solutions for problems in low-income communities drawing ideas from cultural, environmental, and economic beliefs. It focuses on improving the lives of a wide group of individuals in a way that will contribute to the development of a country as a whole.
 
Using the five stages of design thinking, the project came into fruition but there is much work that still needs to be done. Design Thinking is the science of realizing and critically analyzing a certain issue and working towards creating a solution that is greater than already existing or attempted conclusions. This term is often broken down into five categories: Empathize, Define, Ideate, Prototype, and Test/Iterate. During my design process, I used these five categories to guide my project.
 
 
Inspiration and background
The inspiration to work on designing a prosthetic socket came from my experiences as an above the knee amputee living in Rwanda. Rwanda is a developing country with a population of approximately 11 million. Unfortunately, there are no known statistical data to indicate exactly how many amputees there are in Rwanda, but a large number of the population were left handicapped due to the 1994 genocide that took the lives of more than 800,000 innocent people. Like many handicapped people in developing countries, amputees in Rwanda are at the bottom of the poverty line and therefore do not bother thinking of buying a prosthetic limb due to their high prices.
 
The cost of a prosthetic limb in developing countries varies greatly depending on the materials used and the region in which they are made. However, according to an article published on the Orthotics and Prosthetics (OandP) website, the overall cost of a prosthetic limb in low income countries ranges between $125 and $1,875. This price range is still a challenge for many third world country amputees as the average annual income per family living in rural areas is close to or less than $300.
 
General Prosthetic leg structure
The most common types of lower extremity amputations are done above or below the knee. My research focused on designing a prosthetic socket for individuals who are missing a limb above the knee. A typical prosthetic socket for an above the knee amputee consists of four different compartments:
  • A socket, which is the part that comes in direct contact with the amputee’s residual limb. It is considered the most important piece of a prosthesis because an amputee will not use their whole artificial limb if the socket does not feel comfortable.
  • A pylon, the limb extension, sometimes it is part of the knee.
  • A knee, the piece between the pylon and the prosthetic socket.
  • A foot. 
 
Traditional and CAD/CAM methods
Today, prosthetic limbs are commonly made using conventional methods. This is where a prosthetist takes a 3D shape of the residual limb by wrapping a plaster cast around it to get a negative mold. He/she then generates a positive mold from the negative on which anatomical points are identified for even load distribution. Throughout this process, the prosthetist uses little quantitative analysis to design the socket, and as a result, the comfort level of the prosthetic socket depends on how experienced the prosthetist is. Fortunately, some prosthetists have adopted the use of computer aided design and manufacturing methods for more comfortable prosthetic sockets. However, even with CAD/CAM processes in place, most prosthetic sockets created today cause discomfort because of the daily volume changes that an amputee’s residual limb experiences. 


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Getting my leg cast by my prosthetist.     

 

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A 3D negative mold of my residual limb.

Workflow
In my design, I used ReMake and Fusion 360 to tried to explore different ways one can design an adjustable prosthetic socket that is comfortable and can adjust to fill in the gaps caused by daily volume fluctuation. I wanted my design to answer a question that other CAD/CAM users have not been able to answer well, which is the question of adjustability. To achieve my goal, I had to apply design-thinking methods each step of the way.  
 
Empathy, Define, Ideate, Prototype, Test
The first step of this project was to get to know the people I wanted to design for as well as I could. This was not very easy, since the goal is to design for amputees in the developing world with whom I unfortunately have no direct contact. Nonetheless, information from the internet and other established organizations like D-Rev, as well as feedback from current amputees living with prosthetic sockets in the U.S helped give me a good sense of what direction I should take with this design. The direction this prosthetic design project took was also greatly influenced by my experience as an amputee.
 
After identifying who the users would be, it was important for me to define their most pressing problem. As is the issue I had myself, it turned out to be the discomfort in the prosthetic socket when the amputee starts losing weight or gaining weight. Another issue that kept coming up was the sweating of the residual limb in the liner. A liner is a silicon material that an amputee puts on right before they wear their rigid prosthetic socket. It is there to prevent the prosthetic socket from rubbing on the amputee’s skin, or causing any damage. However, once an amputee starts feeling volume changes in their prosthetic socket, skin breakdown can occur even with the liner if the amputee does not act quickly to get a new prosthetic socket, or add ply socks to fill in for the lost volume. Unfortunately, while the addition of ply socks is the current best answer for amputee’s volume fluctuation, overtime, there might be pressure build up in areas where the socks are more concentrated than others. Eventually, the ultimate solution is for the amputee to pay for a new prosthetic socket.
 
Below is a graph indicating responses from current prosthetic socket users in the United States showing when and how many sockets they have owned over however many years they have been amputees. Each bar represents one person. There were 14 responses in total and many of the responders indicated that they have owned “a lot” of prosthetic sockets in those specific years. There were three different people who indicated that they have been using a prosthetic socket for 8 years, and another three who had owned some for 10 years. As indicated in the graph, I chose 25 to represent the response “a lot” as I did not know how to categorize the word in numbers. 
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After analyzing all the current problems amputees are facing today with their prosthetic sockets, this is the mission statement I came up with: To develop a cost effective transfemoral prosthetic socket that is durable and adjusts to comfortably distribute load across an amputee’s residual limb despite day to day limb shape, size, and volume fluctuation.
 
While this statement is trying to respond to the challenges of affordability, durability, and adjustability, my focus was adjustability. I believe if we can make a prosthetic socket that adjusts to comfortably distribute load across an amputee’s limb despite the daily changes the residual limb goes through, then we are solving the issue of cost as the amputee will not have to buy multiple sockets in just a year or two.
 
This whole process required me to make numerous sketches and prototypes as I thought through my design statement.
 
These are a few of the sketches chosen from the multitude of sketches I did.

 

Prototyping was one of the most important parts of my design process.

 
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In addition, I had to go to my prosthetist in order to get a plaster mold of my residual limb which concisely captured the whole geometry of my limb. Using my iPhone 4s camera, I took pictures of that residual mold at a 3600 angle making sure to stay parallel to the limb and within the same distance. I did the same procedure for the top of the mold and then I uploaded the images into ReMake, which was able to make a 3 dimensional mesh of the limb. I edited the mesh by cutting off all the unnecessary parts that the camera had captured until the mold had the shape of a socket. I then changed the triangular mesh into a quad mesh and reduced the geometry to 1000 quads so that it would be simpler to work with in Fusion 360. I was then able to import the 1K quad mesh into Fusion 360. Once the quad mesh was in Fusion 360, I cleaned it up a little more and got it to the size and shape that I wanted using the right measuring tools. I then offset the mesh and thickened it to give it more depth in its walls and overall geometry. I continued to edit until the socket looked like what you see in the third picture below with a buckle system for adjustability. Eventually, I want the prosthetic socket I create to fit as well as the prosthetic socket in the last picture, but with more room for adjustability to accommodate volume changes.

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Images indicating the tools used in my design process from picture taking to designing in Fusion 360.
 
Testing
Testing will be the next step of my design process. As of right now, the image you see above in Fusion 360 has not been 3D printed for testing yet. More designs will be made in the future to better improve the comfort level of the prosthetic socket. I also need to do some quantitative analysis to determine how much load the socket should be able to handle and where the pressure points should be according to my residual limb geometry. ReMake and Fusion 360 have the potential to change the standards of prosthetic limb design for the better. With these tools, great design can be achieved especially when designing for social impact. Once this prosthetic socket has successfully been designed and is ready for use, impact will be measured by keeping count of the number of users in the developing world who will be able to use it with great comfort and success.               
 
Reference:
http://www.advancedamputees.com/amputee-statistics-you-ought-know
http://www.lowcostprosthesis.org/the-need
https://newrepublic.com/article/117398/rwanda-genocide-photos-amputees-20-years-later
http://www.oandp.org/publications/resident/pdf/DevelopingCountries.pdf