1 Active Ankle Foot Orthotic Department of Biomedical Engineering BME 201 Final Report May 9, 2007 Client: Dr. Robery P. Przybelski Advisor: Brenda Ogle Erin Main – Co-Team Leader Jessica Hause – Co-Team Leader Josh White – Communications Emily Andrews – BSAC Tony Schuler – BWIG2Table of Contents Abstract……………………………………………………………………...3 Background……………………………………………………………….....3 Specifications………………………………………………………………..8 Previous Work..…………………………………………………………….12 Design Ideas Spring Design………………………...……………………………...13 Joint Design …………………………………………………………14 Material Design …..…………………………………………………17 Design Matrix………………………………………………………………19 Materials and Methods……………………………………………………..20 Final Design……………………………………………………………......23 Testing………………………………………………………………...........25 Cost Analysis………………………………………………………………27 Future Work………………………………………………………………..28 Appendix A: References..………………………………………………….29 Appendix B: PDS...………………………………………………………...303Abstract In the beginning of the semester, our client, Dr. Robert Przybelski, was urged to propose the active ankle/foot orthotic project at the request of one of his patient, Stefani Morgan. His patient, suffering from a medical condition known as foot drop, was very dissatisfied with the orthotic she was currently using and was hopeful that our design team could improve upon it. The orthotic she used only addressed the basic problems associated with foot drop, such as supporting ankle weakness and holding the foot at a fixed position of 90 degrees to the ankle. It was also very bulky and did not easily fit in a shoe. This design only prevented the foot from “dropping” and made walking very uncomfortable and awkward. In fact, the device was so cumbersome, the patient preferred to walk without it. Leading a very active lifestyle with a passion for hiking, the patient was seeking an orthotic that more closely simulated a normal human gait pattern and actively enhanced the walking motion, helping the user by increasing push-off from step to step. With this is mind, it was our team’s goal to design an orthotic that not only supported ankle weakness and held the foot in a fixed position, but also actively enhanced walking and improved balance and proprioception. Background Thousands of people worldwide are afflicted by diseases that affect their normal gait pattern. Several neuropathies that commonly cause walking abnormalities are stroke, Charcot-Marie-Tooth Disease (CMT) and multiple sclerosis (MS). Each of these diseases afflicts the patient in a different manner; stroke affects the patient by depriving the brain of essential nutrients while CMT and MS affect the peripheral nervous system.4Figure 1: Depiction of the nerve cells, axons, myelin sheath and muscle fibers of the arm. Stroke is an illness that strikes a person when a part of the brain is prevented from receiving oxygen and other essential nutrients from the bloodstream. The two primary types of stroke are ischemic and hemorrhagic stroke. Ischemic stroke occurs when a blood vessel supplying blood to the brain is blocked, suddenly disrupting the blood flow to the brain. As a result, the part of the brain being supplied by this blood vessel dies. On the other hand, hemorrhagic stroke occurs when the brain itself bleeds and blood spills into the spaces surrounding the brain cells and suffocates parts of the brain. Although the types vary in their origin, they both prevent the brain from receiving nutrients and cause part of the brain to die. Once a region of the brain dies, the body loses all functions that were controlled by that area of the brain. The severity of a stroke depends on the region of the brain that was affected as well as the size of the region that was affected. While they can range from mild to severe, the symptoms that primarily affect a normal walking pattern are partial or complete paralysis as well as problems with vision and proprioception. While stroke affects a person’s ability to walk through brain death, Charcot-Marie-Tooth affects normal gait because it afflicts the peripheral nervous system. The main components of the peripheral nervous system are the nerve cells, axons, myelin sheath and muscle fibers (Figure 1). Normally, the nervous system relays messages5between the brain and muscle fibers via electrical signals through the axons. The axon is surrounded by myelin, which is responsible for insulating the axons from the surrounding cells. By acting as an insulator, the myelin protects the structure of the axon and prevents the electrical signal from dissipating as it travels further distances. Damaging the myelin causes the electric impulses to be conducted more slowly than normal; and harm to the axon itself causes the strength of the signal to be reduced. CMT is a disease that causes mutations in genes responsible for the structure and function of both myelin and axons. CMT1 and CMT2 are the most common variations of the disease; CMT1 causes mutations in the myelin and CMT2 causes mutations in the axons. Other variations of the disease result in a more severe affliction or a combination of the mutations. Because the myelin and axons are mutated in Charcot-Marie-Tooth, the nerves slowly begin to degenerate and lose the ability to transmit signals from the brain to the limbs and vice-versa. As the ability to communicate fades, the motor nerves at the end of the axons function to a lesser extent and as a result the person afflicted with the disorder experiences increased muscle weakness and atrophy. Because the patient has increased muscle weakness, he/she often has an increased difficulty in walking because of the lack of ability to balance, propel oneself forward and support his/her weight. Although multiple
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