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Background
Being able to move without pain is often something we take for granted. Severe joint pain can make daily activities extremely difficult, and when it occurs in the ankle it can majorly affect one’s ability to walk. This can happen with pathologies such as diabetes, rheumatoid arthritis, osteoporosis, and severe fracture. A common treatment for severe ankle arthritis is called ankle arthrodesis. Ankle arthrodesis, or ankle fusion, is the surgical process of fusing the ankle bones together. It’s effective at reducing pain, but at the expense of joint mobility, and sometimes the mobility limitations are so extreme that patients will opt to amputate the foot instead.
The goal for this project was to design a solution that would compensate for the loss of inversion and eversion (side to side motion) in patients with ankle fusion. A successful product would allow the user to maintain zero degrees of side to side ankle motion while walking on non-flat surfaces.
For our solution, we took a soft robotics approach. The patient's shoe is connected to two parallel soles on a hinge. On either side of the hinge there are two air sacs that can inflate and deflate, actuating to adjust the angle of the soles relative to each other. This mimics inversion and eversion. Success was measured based on the ability for the top sole to maintain a position of zero degrees from the horizontal.
When traversing over rough terrain, the device compensates for loss of mobility, increasing the capacity for ankle fusion patients to enjoy everyday activities. The power supply and air compressor would be stored in a backpack for a practical application.
The system is controlled using solenoid valves to supply air to each sac, actuating the device. A gyroscope at the center of the top sole indicates the angle of deviation from zero degrees, and the corresponding actuator inflates to compensate. Air is provided by an air compressor.
Validation Testing
We tested the efficacy of the device at different angles. Reading values from the gyroscope in the center of the top sole, the desired angle was zero with the system powered on. Trials were taken for each angle, with the pneumatics powered on or powered off, and with weight at different locations on the sole. The weight placement was done in consideration the redistribution of mass as a person takes a step.
Three trials were taken for each scenario over a period of five seconds, and the results were averaged.
For the tested angles, we found a statistically significant difference when the dynamic controls were applied. Thus the device is able to hold the top sole at an angle of zero degrees, successfully compensating for loss of ankle mobility.
Future Goals
This device successfully achieves the goal of compensating for inversion and eversion, and is capable of supporting the full weight of a person. A more fine tuned version of this device would implement a higher flutter rate for the solenoid valves, maintaining a more steady air pressure in the actuators and more precise movement, which would require higher quality electronic materials. Additionally, reinforcements could be used outside of the air sacs to prevent rupture.
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