Prosthesis Given New Perspectives By External Power
Following is an abstract of a report by E.D. Sherman, M.D., A.L. Lippay, B. Eng., and 6. Gingras, M.D., of modifications being made on the Soviet bioelectric arm at the Rehabilitation Institute of Montreal in Canada. The report originally appeared in Hospital Management, November 1965.
When the thalidomide tragedy struck Canada, the Rehabilitation Institute of Montreal was one of three institutions selected by the government to provide treatment programs for the affected children.
In 1964 the Soviet Union announced the development of a bioelectric arm. In July of that year a four-member team from Montreal visited the Central Institute for Prosthetics and Prosthetic Development in Moscow to explore its possibilities. In October, through a special assistance grant from the Quebec Provincial Government, the manufacturing rights and 10 prototypes of the Soviet arm were purchased.
A pilot project to gain practical and clinical experience with the Soviet device was initiated at the Institute. The ultimate objective was the application of myoelectric control to prostheses for child amputees, including those of congenital origin. A preliminary report on their experience follows:
The Soviet Bioelectric Arm
The active element of the prosthesis is the handpiece, which contains a motor and drive in the metacarpal area. A 13,000 rpm 1.5 watt motor drives a gear reducer and rotary-to-linear converter. The fingers and thumb, which are linked to the drive, are rigid, slightly flexed, and hinged at the metacarpophalangeal joint. In the closed position, finger tip prehension occurs approximately in the midline of the forearm, with a pinch force of four pounds. The hand opens and closes in 0.8 second.
A cosmetic glove generates sufficient friction to hold a drinking glass or other objects varying in diameter from 1/4" to 3-3/4". The grasp is firm enough to hold a knife and cut a steak, and delicate enough to hold a match to light one's pipe.
The system is powered by a 13.75-volt battery, sufficient for the activities of at least one long day, rechargeable overnight.
Cold tests carried out in the RCA Laboratories in Montreal showed little change in performance between 100 degrees and 0 degree F. The mechanical noise caused by the drive is audible but hardly objectionable; in fact, it provides the amputee with an indication of activity of the hand even when visual observation is not possible.
Whenever a controlling muscle contracts, its action potentials are detected by surface electrodes. This small electric signal is increased in value by the amplifier and turned into a direct current. Whenever this current is of sufficient strength to operate a small relay, the motor is switched on to run in the corresponding direction. Another control site, i.e., muscle, operates an identical channel to switch the motor in the opposite direction. Thus the hand may be opened or closed by contracting the corresponding muscle, whether movement occurs or not.
The Institute added an adjustable wrist unit to provide passive wrist rotation. The amplifier was removed from its original casing and relocated either inside the socket or on its surface. All wiring was internalized except the power lead to the battery.
The original electronic system contained many components with marginal ratings, causing an excessive number of failures. When American hardware was used for replacement parts, these failures largely disappeared. Two new amplifiers and a new battery charger were designed, with several new battery configurations to facilitate installation on the patient and to enhance comfort and accessibility.
The electrodes now incorporate the neutral plate as a third contact to the skin, eliminating the need for a separate electrode and wiring. These and other minor changes are currently undergoing evaluation in actual practice. A new type of electrode seems to operate satisfactorily without electrode paste. To operate the hand in the desired manner, the development of control points capable of functioning individually is essential. Using the "natural" muscles--the flexors and extensors--to control opening and closing of the hand reduces the training and adaptation period, but any available muscle can be substituted.
The patient's phantom sensation may be used to advantage during training. The action of control muscles is remembered and repeated more accurately when associated with the past body image.
Significant improvements in the amputee's mastery of control sites can be
achieved through visual display. For myoelectric activity, an indicating meter appears to be the best choice. One blind subject, however, was successfully trained by substituting audible signals for visual display. The usual loudspeaker output of electromyographic amplifiers was channelled in his ears to represent the opening and closing of his hand. This amputee required only 12 minutes to produce consistent signals without the usual mistakes of sighted subjects.
Evaluation of functional capacities without prosthesis is performed initially. This evaluation is concerned primarily with the activities of daily living. A unilateral amputee seldom presents major problems with routine tasks, while the bilateral amputee is generally considered dependent.
If the amputee is already equipped with a prosthesis, assessment is made of his performance in its operation and control in the activities of daily living. Unilateral and bilateral activities are observed in all ranges with and without resistance.
The Russian prosthesis is adjusted for proper electronic operation by the Research and Training Unit in cooperation with the Occupational Therapy Department. The patient is equipped and taught to put on the prosthesis and apply the electrodes. Occupational therapy training is then instituted to achieve opening and closing of the hand in different positions, prehension and release of small and large objects, activities demanding eye-hand coordination, dexterity, and speed, and functional activities, e.g., grooming, eating. Working and wearing tolerance is increased, with frequent examinations of the skin for possible pressure problems.
The hand as presently designed is available only in the male adult size. Further development is needed to miniaturize the prosthesis so that it can be applied to female and to child amputees, as well as to accommodate other Interchangeable terminal devices, such as a hook.
At present the prosthesis performs only two motions: opening and closing the hand. Powered supination and pronation, as well as elbow flexion for above-elbow amputees, are highly desirable future developments.
Research is also urgently required on the further application of electronic principles, including implantation of myoelectric transmitters. The ultimate objective is to equip the limb-deficient child and the adult amputee with a bioelectric limb providing more functions and a greater degree of freedom than is possible with present devices.