Knee-loading device for mri-based patellar tracking
2023
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This was my first-year master's project that was completed in a group of six. We worked in collaboration with Sahlgrenska Academy, the medical faculty at the University of Gothenburg, to aid in an ongoing research study performed by surgeons in the orthopedics department.
Currently, MRIs taken of the knee are taken while the patient is lying down and the knee has no force applied to it. This leads to an inaccurate view of the kneecap during everyday activities, such as walking. Our goal was then to create a device that realistically simulates loaded conditions for a knee while the patient is lying down.
The Problem & Proposed Solution
For those with kneecap, or patella, instability, dislocation can occur from motions as simple as getting in and out of your car and as frequently as every day. This instability is often caused by a convex trochlear groove, causing the kneecap to slide off to the side during bending, rather than following along the center of the groove. The current solution to this issue is a surgery that carves out a new trochlear groove, though it is not customized to the patients actual patellar path.
The research team at Sahlgrenska was looking to develop a device that could lock the knee at different angles during an MRI in order to be able to track the path of the kneecap during bending. This device also needed to put a force onto the knee equivalent to that experienced during walking to ensure that the kneecap's path would be as accurate to everyday activity as possible.
The Design Process
The team underwent a thorough brainstorming and prototyping process, where some of our initial sketches can be seen below for the subsystems of loading the knee, locking the angle, and stabilizing the knee for movement in one plane.
Once prototype testing was complete, the final proof of concept was constructed using primarily wood and metal fasteners. These would obviously not be the proper materials used in an MRI environment as there are issues with sterility and magnetism, but we felt that this would suffice for testing of the design.
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Testing proved to effectively apply load to the knee, by pushing the knee against a board of rubber bands. The head board slides forward and backwards, moving a patient's upper body and subsequently changing the angle of their bent knee. Testing found that handles on the sides would ease in sliding the upper body, and the shin straps should be longer to more effectively hold the knee still. With these changes, a new CAD design was proposed in proper material.