ORTHOTICS
FREEDOM to move
Being mobile is essential for good quality of life. Caryn Gootkin talks to the experts about the innovations within this sector
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rosthetics manufacturers are always looking for ways to improve communication between the body and external prostheses to enable amputees to move as naturally as possible. “Sensors on muscles read signals and give input to the prosthesis to tell it to move in some preprogrammed way,” says Jan Kristensen, academy director of Össur, which develops and manufactures noninvasive orthopaedic equipment. “We always look for ways to give amputees more ‘ranges of freedom’ to allow them to perform more movements. Hand prostheses, for example, now have six motors, one in each finger and two in the thumb, giving users more ranges of freedom.”
PATTERN RECOGNITION
Pattern recognition, the holy grail of prosthetics, occurs when the prosthesis learns to interpret individual muscle movement patterns and assigns specific movements to that pattern. “Pattern recognition involves using more electrodes (or sensors), for example, in the arm, to pick up more signals and signals of different strengths,” says Jan Kristensen. “Through software, we can allocate a certain pattern of muscle signals to the movement the amputee is trying to make with their finger, wrist or elbow. The prosthetist asks their patient to give signals for each type of movement. The software connects to the prosthesis via Bluetooth and in this way, they allocate signals to movements. The user must then replicate these muscle patterns within certain parameters.” Prosthetic knees learn gait patterns and adapt to them, constantly changing speed to match the amputee’s walking speed. “Prosthetic knees have both load and gyro sensors that can adjust a thousand times each second,” says Kristensen. “Össur’s Jan Kristensen bionic knees use pattern recognition via artificial intelligence to recognise how each individual’s body moves. The knee needs to recognise when the walker changes pace or starts walking up or down stairs – walking up stairs demands a different movement to walking straight or down stairs, so the prosthesis needs to know when to extend
the knee because we are walking straight, and when not to extend fully because we are walking up stairs. Algorithms in the knee work with pattern recognition, sending an order back to the harmonic drive in the knee.” Picking up muscle patterns and acting accordingly is far more complex with arm prostheses than for lower limbs. “Our hands perform so many more tasks than our legs; we use a wide range of grips, so the permutations are vast,” says Kristensen. “On top of this, arm prostheses are much smaller than leg prostheses, so we have less space to work with.” The next step is for pattern recognition to happen through implantable myoelectrical sensors, each one the size of a grain of rice. “These are implanted into the muscles, pick up their signals and transfer them wirelessly to the computer in the prosthesis, providing clearer, more reliable signals,” says Kristensen. “In the future, we will see sensory feedback going the other way too, with artificial limbs being able to sense cold and warm, hard and soft.”
“Through software, we can allocate a certain pattern of muscle signals to the movement the amputee is trying to make with their finger, wrist or elbow.” – Jan Kristensen
DID YOU KNOW?
Most prosthetics are constructed with lightweight carbon fibre, aluminium and titanium components. The average prosthetic lasts three to five years. All prosthetics are custom-made to each individual patient, taking several factors into consideration, such as health, lifestyle, age and weight.
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2021/06/09 3:27 PM
