Born with a left arm that ends just below his elbow, 9-year-old Aidan Robinson has had his share of prosthetic arms. As a baby, he wore a passive arm, plastic and immovable like a doll’s arm, which trained his brain to develop motor skills equally on both sides. As he grew, he graduated to more complex prostheses. Most children with an upper-limb difference—a catch-all term used to describe conditions in which limbs don’t develop to their full length—start with a body-powered prostheses, a system which use a series of cables attached to the opposite shoulder to create motion. But Robinson immediately jumped to myoelectric arms, which use electrodes to respond to subtle muscle movements. His first myoelectric arm could open at will but close automatically after a few seconds. His next arm was more complex, capable of reading two types of muscle movements instead of one, closing when he lifted his arm up and opening when he lowered it.
While the science of prosthetics has advanced dramatically, the most sophisticated prosthetic technology is still not available for children. Arms with fingers that articulate or that can do complicated motions like turning a wrist while simultaneously opening a hand often don’t even come in children’s sizes. And for some good reasons. These advanced prosthetics are expensive—basic myoelectric systems start around $15,000—whereas basic, body-powered arms for kids are far cheaper, starting around $5,500. That price difference is particularly significant when you considering that the child might outgrow the arm in a year. Kids also might not have the muscle control needed to use a myoelectric arm effectively. And children simply might not be responsible enough to make sure the arm doesn’t get wet or to charge the battery every night.