A Child's Body-Powered Prehensor with Adaptive Grasp

DESCRIPTION (provided by applicant): Conventional body-powered assistive appliances intended to help children having upper limb deficiencies have proven inadequate for some activities, most notably play. The critical component in these systems that contributes grasp functionality, called a prehensor or terminal device, must strike a balance between functionality for activities children wish to accomplish and cosmesis for parents who desire their child have a normal appearance. Parents most often select more cosmetic devices designed to mimic the anatomical hand, while studies have shown children prefer devices that are more functional. Those who do select more functional devices often find existing units offer disappointing or inadequate performance for play activities as they require too much cable excursion or operate inefficiently and demand too much cable tension to effect grasp. These problems leave many children without an acceptable device at precisely the time they should be learning lifelong prosthetics usage skills. In Phase I, ADA demonstrated the technical feasibility of a prehensor designed specifically for children's daily activities. An adaptive digit was designed that provides the enclosing grasp children primarily use as opposed to high-force pinching grasp common for adults. Also included was a Variable Mechanical Advantage (VMA) grasping engine that efficiently transforms cable excursion and tension into quality, stable grasp. This engine significantly improves the ratio of grip force achieved to the input cable tension (called the forward force ratio, FFR). ADA's prototype achieved a maximum FFR of 0.78, as compared to current devices which average an FFR of 0.2. The end result is that children can achieve higher levels of gripping force with less physical exertion, freeing them to do what they desire most-play. This Phase II effort will focus on refining the proven Phase I prototype design to 1) minimize its commercial manufacturing cost to benefit families of limited means and 2) validate its performance in actual service with children users. To gain commercial acceptance, additional features such as passive holding capacity and improved cosmesis will be incorporated. ADA will work with practicing prosthetists in the Shriners Hospital network through the design phase and into clinical evaluations. By partnering with Shriners, ADA will establish an early, working relationship with the nation's leading provider of child's prosthetic care and equipment. Throughout, ADA will maintain focus on commercial viability by constantly working with outside partners to ensure satisfying children's grasping needs remain central to the effort and in crisp focus. If successful, the Phase II effort will produce a child's prehensor that is functionally superior to all currently available conventional prehensors. To ensure success with parents as well as children, ADA will include market-driven cosmetic features in addition to adaptive grasp, VMA, and passive holding capability. The Phase II effort will leverage this technology to create an entity that will be attractive to Phase III investors. Due to the small market size, children with upper limb deficiencies are made to get by with prosthetics not suited to their special needs. This research seeks to develop a functional prehensor designed specifically to outperform available devices in both daily use and cosmetic acceptance.