Prosthetic Socket
Prosthetic Socket
ME170A and ME170B
For my engineering capstone courses, my team and I were assigned a project aimed at reducing the issues that amputees face from ill-fitting prosthetic sockets.
For my engineering capstone courses, my team and I were assigned a project aimed at reducing the issues that amputees face from ill-fitting prosthetic sockets.
Understanding the Assingment
Understanding the Assingment
Skin issues for amputees stem from both too tight of a socket and too loose of a socket. These issues can make walking unbearable and cause tremendous pain. Our project, as requested by our advisor who is a doctor at Stanford Hospital, was to build a socket that adjusts its tightness based on what stage of the gait cycle the user is in. In a perfect world, the socket would tighten in preparation for the leg being loaded and loosen as the leg swings through. This would increase blood flow and reduce skin issues for the user.
Skin issues for amputees stem from both too tight of a socket and too loose of a socket. These issues can make walking unbearable and cause tremendous pain. Our project, as requested by our advisor who is a doctor at Stanford Hospital, was to build a socket that adjusts its tightness based on what stage of the gait cycle the user is in. In a perfect world, the socket would tighten in preparation for the leg being loaded and loosen as the leg swings through. This would increase blood flow and reduce skin issues for the user.
This is an incredibly challenging problem to solve as the limb and all mechanisms have to be very light, the socket has to go from loose to tight in less than .0375 seconds, and the distribution of load throughout the residual limb of the patient must be distributed evenly in both the tight and loose state to have the maximum effect of decreasing skin issues.
Our primary goal was to prove that we could create a socket that when tightened would decrease the load felt on the end of the patient's residual limb (called the distal tip). The tip of the amputee limb is a particularly sensitive part of their limb and in a well-designed socket holds very little of the user's weight. Instead, a well-designed socket distributes this force onto the edge of the side of the residual limb.
This project required extensive simulation, hand calculations, and MATLAB scripting. Beyond that given it required important simplifying assumptions. I've included some of my hand calculations below that show how I began to simplify an organic unconstrained scenario into a solvable one.
The initial photo shows this testing rig as force is applied by an Instron machine. Present but not visible in this image are a series of pressure sensors that were distributed between the socket and the model limb.
This is an incredibly challenging problem to solve as the limb and all mechanisms have to be very light, the socket has to go from loose to tight in less than .0375 seconds, and the distribution of load throughout the residual limb of the patient must be distributed evenly in both the tight and loose state to have the maximum effect of decreasing skin issues.
Our primary goal was to prove that we could create a socket that when tightened would decrease the load felt on the end of the patient's residual limb (called the distal tip). The tip of the amputee limb is a particularly sensitive part of their limb and in a well-designed socket holds very little of the user's weight. Instead, a well-designed socket distributes this force onto the edge of the side of the residual limb.
This project required extensive simulation, hand calculations, and MATLAB scripting. Beyond that given it required important simplifying assumptions. I've included some of my hand calculations below that show how I began to simplify an organic unconstrained scenario into a solvable one.
The initial photo shows this testing rig as force is applied by an Instron machine. Present but not visible in this image are a series of pressure sensors that were distributed between the socket and the model limb.
This project involved extensive Finite Element Analysis (FEA). The socket was designed to precisely fit a specific amputee's residual limb scan, showcased by the limb's complexity within the socket interior in the above image. The main challenge was to evenly distribute socket displacement upon tightening. The early simulation revealed most displacements occurred at the top (as you'd expect given this shape emulates a cantilever beam), risking blood flow constriction and ineffective load distribution. Thus, design iterations and simulations centered on improving displacement distribution when the socket was tightened.
This project involved extensive Finite Element Analysis (FEA). The socket was designed to precisely fit a specific amputee's residual limb scan, showcased by the limb's complexity within the socket interior in the above image. The main challenge was to evenly distribute socket displacement upon tightening. The early simulation revealed most displacements occurred at the top (as you'd expect given this shape emulates a cantilever beam), risking blood flow constriction and ineffective load distribution. Thus, design iterations and simulations centered on improving displacement distribution when the socket was tightened.
I no longer have access to the documentation for this project as my school email has expired. As a result, I will summarize our work. Our goal was to test how tightening a socket I designed would adjust the load on different points of the limb. This is exemplified in the above image. Given a load, provided by the Instron machine, how much does tightening the socket adjust the pressure on various sensitive parts of the limb? This was tested using pressure sensors laid between the model limb and socket.
What we saw, and wanted to see, was that if you tightened the socket it would reduce the amount of load on the tip of the amputee's limb. Our advisors were very excited about the results we achieved.
These results however taper off as the load gets higher. This indicates that there is a maximum amount of load that can be distributed to the sides of one's amputated limb. Even if you tighten the socket more the force on the tip doesn't decrease. This indicates that at certain forces the squishiness/flexibility of skin and muscle come into play and negate the effects of further tightening. This likely stems from the inaccurate model of the limb that we used more so than a failure of design but there are facets of the design that I would change if given more time to solve the problem.
I no longer have access to the documentation for this project as my school email has expired. As a result, I will summarize our work. Our goal was to test how tightening a socket I designed would adjust the load on different points of the limb. This is exemplified in the above image. Given a load, provided by the Instron machine, how much does tightening the socket adjust the pressure on various sensitive parts of the limb? This was tested using pressure sensors laid between the model limb and socket.
What we saw, and wanted to see, was that if you tightened the socket it would reduce the amount of load on the tip of the amputee's limb. Our advisors were very excited about the results we achieved.
These results however taper off as the load gets higher. This indicates that there is a maximum amount of load that can be distributed to the sides of one's amputated limb. Even if you tighten the socket more the force on the tip doesn't decrease. This indicates that at certain forces the squishiness/flexibility of skin and muscle come into play and negate the effects of further tightening. This likely stems from the inaccurate model of the limb that we used more so than a failure of design but there are facets of the design that I would change if given more time to solve the problem.