Ankle Foot Orthotic Midsemester Report Erin Main Co Team Leader Jessica Hause Co team Leader Josh White Communications Emily Andrews BSAC Tony Schuler BWIG Department of Biomedical Engineering BME 201 Client Dr Robert P Przybelski Advisor Brenda Ogle March 14 2007 Abstract 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 patients 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 stopped 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 and very interested in being able to hike the patient was seeking an orthotic that more closely simulated a normal human gait pattern and actively enhanced the walking motion 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 Stroke is an illness that strikes a person when 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 While stroke affects a person s ability to walk through brain death CharcotMarie 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 Appendix A Figure 1 Normally the nervous system relays messages between 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 Charot Marie Tooth 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 sclerosis is a disease that also affects the peripheral nervous system Appendix A Figure 1 it does so in a different manner than Charcot MarieTooth MS is an autoimmune disease in which the body s immune system attacks the nervous system especially the myelin and axons As the body attacks these cells it produces numerous regions of scar tissue sclerosis that disrupt the signaling between the brain and motor nerves similar to the disruption caused by CMT Because MS affects the body in a very similar fashion to CMT it has many of the same symptoms including the inability to balance and lack of propulsion In addition to the shared symptoms MS also causes patients to lose feeling in their lower extremities making it almost impossible to walk because of lack of proprioception Because these diseases are so common many people are often afflicted with abnormal gait patterns and therefore experts have studied normal gait in order to develop ways to cure these abnormalities The main task of the gait cycle is to translate the individual s center of gravity through space with the least energy possible In order to do so the entire lower half of the body must act as a closed kinetic chain in which the action of one muscle or joint supports the action of another In other words the hip knee tibia ankle foot and muscles and tendons in the leg must all act in conjunction to transfer the body s center of gravity in the most efficient manner possible When one of the above components is prevented from executing its normal function such as the increased muscle weakness caused by CMT and MS a variety of the other joints bones and muscles will work harder to
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