This prosthesis is a reality—the brainchild of Michael Tompkins of Animated Prosthetics Inc., Greensboro, North Carolina, USA. Collaborating with C. Michael Schuch, C.P.O., Director of the Prosthetics and Orthotics Department, Duke University, Durham, North Carolina, Tompkins began designing the device in 1994. Clinical trials began in early 1996, and since then, about 35 patients—both children and adults— have been fitted with the electronic arm.

The prosthesis can "grow" with the patient without being rebuilt. How? As Tompkins and Schuch explain in their paper presented during the 1997 Annual Meeting of the American Academy of Orthotists and Prosthetists, an on-board microcomputer, the ACS (Animation Control System) features many unique methods of monitoring the patient sensors and then controlling the hand and wrist devices. The ACS module, preprogrammed with a power profile which controls the hand accurately and efficiently, is designed to operate most externally powered hands and wrist rotation devices.

Its modes of operation, called TASCs (Techniques, Algorithms, and Strategies of Control), match the components in the prosthesis to the skills of the patient. Two typical TASCs include Voluntary Open Auto Close—also know as "cookie cruncher"—and Voluntary Open Voluntary Close, using a single myo signal, also known as single site dual function. "The prosthetist simply tells the ACS which devices are connected to it, such as the number and type of myo-electrodes, the type of battery and hand, and it does the rest," Tompkins and Schuch noted in their paper. "The ACS even allows fine-tuning to match the requirements of special applications. Any TASC can work on any hand." The system is compatible with Otto Bock and VASI hands, wrist units, and electrodes, among others.

Integral to the system is a device named the PCU (Prosthesis Configuration Unit) which is used to configure and monitor the prosthesis. The PCU is linked by a radio transceiver to the ACS; through its five-inch video screen, the prosthetist can view and modify the prosthesis even as it is being worn. Because of the telemetry link, the PCU does not need to accompany the patient. "Many parameters associated with the arm operation, such as myoelectric signal level, hand speed, proportional or on/off control, maximum grip, number of cycles of operation, etc., can be viewed and modified using this communications link," Tompkins and Schuch reported. The prosthesis then can be easily adapted to users as they increase in strength and skills, saving money and the prosthetist's time.

"[The PCU] basically becomes the ‘window' to the prosthesis," state Tompkins and Schuch. "Some problems previously overlooked or misdiagnosed now become obvious when the data is presented on the PCU screen. Data is presented both graphically and numerically to allow exact tracking of the patient's progress." The PCU also can be used for initial patient myo signal evaluation, eliminating the need for other myo-tester devices.

The ACS also stores diagnostic information, such as the number of open/close cycles and battery recharges so the prosthetist can tell exactly how much and how effectively the limb is being used—a valuable source of documented outcomes information for third-party payors.

The ACS controls the charging of the battery for maximum performance and optimal life. Another key to improved function is the battery type: the lithium-ion/lithium-polymer batteries are lighter and more powerful than nickel-cadmium and nickel-metal hydride types. The batteries come in four sizes and mount inside the prosthesis. These improved batteries also have no "mem-ory" problems and can be recharged at any time without fear of damage or loss of battery life.

The improved battery technology along with the ACS power management features extend the operational time from two to four times as long as previous systems; typical recharge times range from one to two hours depending on battery size. Although the initial cost of the control module is somewhat more than for a pediatric myoelectric unit, the overall system cost is comparable to others on the market, according to Tompkins. The company sells its products only to "animation specialists"—prosthetists who have completed its training course. The learning curve is not extensive, says Tompkins; prosthetists can learn how to use the diagnostic equipment for design and modification in just a few hours. For more information, contact: Animated Prosthetics, Inc., 2907 Pacific Avenue, Greensboro, North Carolina 27406 USA; (336) 691-9000; fax: (336) 691-9095; e-mail: info@anipros.com; Web site: www.anipros.com.