MARCH 12-15, 1997 -  SAN FRANCISCO, CA

REVOLUTIONARY CONTROL AND BATTERY SCHEMES FOR
EXTERNALLY POWERED UPPER LIMB PROSTHESES:
UPDATE AND CLINICAL CASE PRESENTATIONS

C. Michael Schuch, C.P.O., F.I.S.P.O.
Duke University Medical Center
Durham, North Carolina

Michael E. Tompkins
Animated Prosthetics, Inc.
Troy, North Carolina

     The introduction consisted of a microcomputer based module called the ACS (Animation Control System), new rechargeable batteries based on lithium- ion/polymer technology, and a unique method of configuring and monitoring the prosthesis using a device named the PCU (Prosthesis Configuration Unit). These devices provide new tools for the prosthetist to diagnose and solve many of the problems associated with the fitting and operation of the prosthesis. As will be shown later, patients that were previously thought to not be candidates for externally powered prostheses are now functional with hands and wrist rotators.

     The ACS module is designed to operate most externally powered hands, child or adult, and wrist rotation devices. Regardless of the hand used, power management and energy conservation are primary features of this product. The module is pre-programmed with a power profile for each hand that is used to control the hand accurately and efficiently. The voltage applied to the patient sensors is constant, independent of the battery voltage. Without this feature, patients have to make stronger signals to achieve the same effect from the hand as the battery discharges. The ACS also controls the charging of the battery for maximum performance and optimal life. Diagnostic information about the prosthesis is stored in the ACS which can be retrieved by the prosthetist. A wireless telemetry link allows the ACS to communicate with the PCU to provide monitoring and configuration, even while the patient is wearing the prosthesis. 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.

     The ACS has many unique methods of monitoring the patient sensors and then controlling the hand and wrist devices. These methods of operation are called TASCs (Techniques and Strategies of Control). TASCs match the components in the prosthesis to the skills of the patient. Typical TASCs include Voluntary Open Auto Close, also known as "cookie cruncher", Voluntary Open Voluntary Close using a single myo signal, also known as single site dual function, plus many more. 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. The ACS even allows fine-tuning to match the requirements of special applications. Any TASC can work on any hand.

     The rechargeable lithium battery is lighter and more powerful than previous technologies. Initial testing of these batteries and the ACS power management features, indicate that the patient will receive 2 to 4 times the operational time compared to previous systems. The battery also contains electronics to protect it from abuse and accidental shorts. These batteries have no "memory effect" and can be recharged at any time without fear of damage or loss of overall life. Typical recharge times range from 1 to 2 hours depending on the size of battery used.

     The PCU is a portable device that contains a video screen to allow the prosthetist to visually interact with the prosthesis. It basically becomes the "window"to the prosthesis. Some problems previously overlooked or mis-diagnosed 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 can also be used for initial patient signal evaluation, eliminating the need for other myo-tester devices. In early 1996, clinical trials with the Animated Prosthetics ACS system were initiated on selected patients at Duke University Medical Center. To date, six amputees have been fit with this system. Four are transradial amputees, one of whom is a child with a congenital deficiency. Two are transhumeral amputees, both a result of trauma. The six cases include one young child fit with her third prosthesis, three adults fit with their first prosthesis, one adult fit with his third prosthesis (second myoelectric), and one older gentleman who came to Duke from Boston wearing a 25 year old wooden plug fit prosthesis.

Case One: Elizabeth
     Elizabeth is a female in her mid thirties who was referred to Duke from the University of North Carolina (UNC) Medical Center where she had undergone a right, upper quarter transradial amputation secondary to tumor. Elizabeth is a graduate student at UNC, earning her Ph.D. in Urban Planning. She was well informed and presented the request at her first appointment for a myoelectric prosthesis with two site, four function control (hand open/close and wrist rotation). Further, she desired that control of the hand and wrist function be independently accessible. To be more precise, she sought to control the four functions with four independent muscle activities. She did not wish to be restricted to shifting from hand (open and close) to wrist (supination and pronation) and/or back again. Even after advice about the difficulty of starting with such a complicated scheme, she insisted that the first prototype fitting include the two site, four function control scheme. The control scheme is as follows:

• dorsal side, former wrist extensors:

- soft contraction = hand opening
- hard contraction = supination

• volar side, former wrist flexors:
  -soft contraction = hand closing
  -hard contraction = pronation

     On the day of the first prototype (trial) fitting, all function were made available to Elizabeth. As suspected, the options were too much too early, but it was felt that Elizabeth needed to experience this overload and reach this conclusion on her own. Then, with the unique qualities of the Animated Prosthetics microcomputer control system, her control scheme (TASC) was reprogrammed, while she still wore the prosthesis, to dual site, two function, digital control (digital or single speed hand opening and closing; the wrist rotator was electronically excluded). This control scheme is simple and allows the user to experience easy early success in hand control. After 10 - 14 days experience with this scheme, the control of the myoelectric prosthesis was advanced to proportional control (speed of hand = to EMG signal input; soft or low EMG signal = slow, controlled hand response, hard or high EMG signal = quick hand response). After this intermediate control scheme was mastered, (four to six weeks time), the scheme was advanced to permit the additional function of wrist rotation, using an Otto Bock wrist rotation unit. While the ACS has four unique TASCs to operate the hand and wrist, the scheme described previously (independent, two site, four function control) was selected. Elizabeth had total command of the prosthesis within two months time. This progression of function control and eventual independence of each of the four motions is only possible with the Animated Prosthetics PCU and microcomputer control module. Elizabeth became such a master of control and use of this prosthesis that she later dictated to us the specific settings for each threshold of the four functions. This was done with her wearing the prosthesis and the settings being altered via radio telemetry by the PCU. She was able to immediately test the new settings and decide if they were to her satisfaction or not. This ability to fine tune, remote and live, is unprecedented. This capability, with an experienced and intelligent myo- prosthesis user is quite challenging and gratifying.

Case Two: Ashley
     Ashley is now just past three and a half years of age. Born with an upper one third level, complete congenital deficiency of the left forearm, she has been followed at Duke since her third month after birth. She has progressed through a passive prosthesis, fit at six months of age; a single site, voluntary opening- automatic closing (cookie cruncher) myoelectric prosthesis, fit at 14 months of age; and her current dual control, proportional myoelectric prosthesis, fit at 28 months of age. Her current prosthesis, which is her third, includes the Animated Prosthetics component system. This system allowed us the ability to progress from a "cookie cruncher" control scheme to a dual site, dual function control system with ease. If Ashley would not have been able to operate a dual control scheme, the PCU would have allowed an instant ability to reprogram the control scheme back to a "cookie cruncher" mode. However, on target with developmental milestones, Ashley was ready to learn dual control. The Animated Prosthetics system allowed us to progress her from an initial mode of digital control with single hand speed and limited grip strength to a proportional dual site/control mode with increased grip strength. Over the course of several weeks and several office visits, we fine tuned her hand speed and grip strength. Unique to the Animated Prosthetics systems, we took advantage of her high surface electrode site output and opened the range of proportional capability by setting parameters with the PCU. Her ability to vary hand speed is the widest range the authors have ever experienced.

Case Three: Girija
     Girija is a 44 year old male, who when seen in mid 1996, was one year post amputation of the right arm, at the transhumeral level. He was from the country of Nepal and was never fitted with a prosthesis, because, as he stated, "the technology was not there." He was in the US as a Hubert Humphrey Fellow at the University of North Carolina studying urban planning and learned of our myoelectric service at Duke. Due to his impending return to Nepal, we did not feel comfortable with a totally externally powered system, so we chose a hybrid system of body powered elbow control and myoelectric hand control. The ease of fine tuning the controls settings and this individual's motivation allowed us to add a wrist rotator system immediately, and by the second day, Girija was performing exactly to his own verbal commands with independent two site, four function control. His battery life per charge was typically three to four days.

Case Four: John
     John is an amputee of 30 years who discovered our myoelectric program and became a self-referral from Boston. He was wearing a 20 plus year old wooden, plug fit prosthesis. All attempts at refitting his arm prosthesis had failed over the last 20 years. His program developed in distinct periods marked by his ability to travel from Boston to Duke. In three periods of three days duration each, he was able to progress with his first ever myoelectric fitting, from digital control to proportional control. At the time of this writing, the plan is for him to return in one month for the addition of a wrist rotation unit and control scheme. Almost 70 years old and wearing a prosthesis over 20 years old, he was undaunted by the options offered by the Animated Prosthetics systems.

Conclusion
     The options available to the prosthetist and the amputee myoelectric user with the Animated Prosthetics systems are unparalleled. The ability to alter control settings and thresholds from a live and remote monitor allows the prosthetist to literally dial in a highly fine tuned and customized control scheme for the individual user. In each of the six cases fit to date, battery life has exceeded expectations, allowing more than a full day of use when needed, and in some cases performing for up to four days. Nightly recharge cycles, as recommended, have not produced the decreasing battery memory problems familiar with Ni-Cad batteries. Credit also goes to other component manufacturers, such as Otto Bock and VASI, whose hands, wrist units, and electrodes are still the standard for those given components. The Animated Prosthetics systems are designed to work in concert with those devices.