A Recent Article Of Interest
EDITOR'S NOTE: One of the most promising of the never developments in prosthetics is the use of bioelectric currents generated in the neuromuscular system as a power source to produce and control movements of artificial arms and legs.
The Russian "bioelectric" hand, which is actuated by myoelectric currents, has been widely publicized. A report, by Dr. F. Brohmke, Federal Minister of Labor and Social Affairs, Bonn, Germany, concerning this item originally appeared in the Orthapadie Technik in November 1964. Dr. Brohmke's report has been translated by Dr. Gabriel Rosenkrantz, and will appear in the 1965 issue of the Veterans Administration Bulletin of Prosthetic Research under the title "Travel Report of a German Delegation of Prosthetic Experts, on the Bioelectric Below-Elbow Prosthesis in the U.S.S.R." The following abstract is based on Dr. Rosenkrantz' translation.
At the invitation of the V/0 Lizen-sintorg firm in Moscow, a delegation of West German prosthetic specialists visited the U.S.S.R., from July 29 through August 5, 1964, to negotiate a contract licensing the production of the Russian bioelectric arm prosthesis in Germany. Lizensintorg manages the sale and licensing of patents of Soviet inventions, and the purchase of foreign patents. The organization is financed from these sources rather than by Government subsidy, but the licensing fees do not reflect developmental costs (which are presumably borne by the government).
At the first meeting in the Ministry of Foreign Trade with the Lizensintorg representatives, the German delegation -- although sponsored by the Federal Ministry of Labor and Social Affairs (BMA) -- explained that the German contract partner would be a private company since the manufacture of orthopedic appliances is not nationalized in the Federal Republic as it is in the U.S.S.R. They stressed, however, that their interest was not in commercial discussion alone but also in an exchange of scientific information with Russian researchers.
PROSTHETICS IN THE U.S.S.R.
Later, the German delegates were given a thorough briefing on the system of manufacture and distribution of prostheses and the care of amputees in the U.S.S.R. Each of the fifteen Republics, of which the Russian Soviet is the largest, has its own Ministry of Health supervising a government workshop for the production of prostheses and braces; and other aids ranging from artificial eyes to wheelchairs. Most of these workshops employ between 50 and 80 workers; and they are usually connected with a hospital that has an amputee training school. Mobile workshops cover the more remote areas. Each amputee is given both a cosmetic and a work prosthesis which are used for at least two years before re-placement.
A specialized technical school in Leningrad provides training for orthopedic technicians in a four year course following high school. The emphasis is purely technical with no prerequisite courses in arts or sciences required. Postgraduate training is given at an appropriate institute.
In the Russian Soviet Republic alone, with a population of 100 million, there are about 360,000 disabled who require 180,000 prosthetic and orthopedic appliances each year. The Moscow workshop - the largest in the U.S.S.R.-has 600 employees.
At the Central Prosthetic Research Institute in Moscow, the delegation made a close study of the bioelectric hand, and also observed functional endurance tests of all components, laboratory testing of electronic circuitry and amputees wearing electrodes for training in myoelectric control. They were also shown biomechanical studies of gait, using electromyographs, treadmill and force plates, similar to studies being made at the Max Planck Institute in Germany and the Institute for Biomechanics in California.
At the Institute for Prosthetic Research in Leningrad, the German specialists paid particular attention to the pneumatic hand now in an early stage of development there, with a view to comparing it to the German pneumatic hand.
The pneumatic above-elbow prosthesis demonstrated has a mechanical elbow-joint, and a passively adjustable mechanical hand-closing joint. It is activated by a pneumatic servomotor (called a diaphragm pump by the Russians) which provides a finely graduated gripping strength. The control valve, in the upper part of the above-elbow socket is activated by a shoulder pull cable. Since the Russian hand lacked feedback, the Germans sketched a diagram of the Heidelberg valve system to explain the automatic feedback of the Heidelberg arm.
The CO2 cartridge of the Russian pneumatic above-elbow prosthesis was located in the forearm. The cartridge with pressure reducing valve was not entirely satisfactory to the Russians and efforts are being made to improve it. During the discussion, the need for development of muscle and contact valves as well as of wrist rotators and elbow joints was particularly emphasized.
In Leningrad there seems to be a lag, compared to Moscow, in familiarity with some of the newer devices and techniques. However, they are using synthetics, interchangeable upper extremity terminal devices (including not only the hand and hook, but also special tools such as a shovel which can be mounted at the elbow joint), and a kind of building-block system for shortening and lengthening prostheses.
Of special interest was the Leningrad hook, which has no thumb. This terminal device is activated by a shoulder pull harness, the pull being transmitted through a reverse joint in the forearm of the prosthesis to a pressure rod which opens the hook. The Germans pointed out that the design could be readily adapted to pneumatic operation, particularly for shorter stumps. The problems and applications of the pneumatic wrist rotation joint were reviewed in this connection.
Next the Delegates visited the Central Institute of Orthopedics and Traumatology in Moscow, which is a large ortho-pedia traumatology hospital with 600 beds. In 1963, a new building with 400 beds was completed. More new buildings, including one with 200 beds for children, are planned for 1965. The Institute also includes theoretical institutes in Anatomy, Pathology, Histology, Limb Transplantation and Metallurgy, which work in close collaboration with the hospital to further the development of orthopedics and traumatology. A Rehabilitation Center, about 50 km. from Moscow, is also affiliated with the hospital.
The Central Institute with its 600 beds was subdivided into 20 independent units, each under the direction of a professor who is a specialist in his field. The smaller independent divisions of about 30 beds were comparable to a "station" in a German hospital. At every division there were four more doctors, comparable to the German Assistant Physicians; thus 100 physicians were assigned to 600 patients.
The Director, Prof. Volkov, suggested an exchange of medical publications, and expressed his regret that the Russian Journal for Orthopedy, Traumatology, and Prosthetics was so little known in the German Republic. It was mentioned that this journal might be produced in English and German supplements, a suggestion that should be taken up promptly.
Throughout their stay, the visitors made every effort in a few days time to gain insight into the development of orthopedic technology in the U.S.S.R., with emphasis on the bioelectric below-elbow prosthesis which was the specific object of their trip.
THE BIOELECTRIC HAND DESCRIBED
The German Delegates found that in its present form, the bioelectric prosthesis conformed quite closely to the illustration shown in the Lizensintorg catalog. It consists of a hollow plastic hand with the four fingers in medium flexion position and a movable hollow plastic thumb. A plastic cosmetic glove is worn with it. In the body of the hand is a small high-speed electric motor of about 1-1/4" radius and 7/8" height, which when actuated moves the thumb toward the fingers.
Gears open and close the thumb to contact the second and third fingers, producing a gripping strength of 2.9 to 3.3 pounds. This can be increased to 4.4 pounds by multiple fist-closing impulses to overcome the free play in the gears.
The power source is a cadmium-nickel storage cell, plastic-encased, weighing 11.3 ounces, which requires recharging every two to three days on 127 or 220 volt a.c. current.
Two electrodes fastened in the plastic stump socket with springs are placed in contact with the flexor and extensor musculature near the elbow, and a third neutral electrode similarly fastened is applied to the skin (close to the ulna). The myoelectric currents produced by muscle contracture are picked up by the electrodes and are amplified to a point where they switch on the electric motor. The amplifier used is transistorized, weighs about 4-l/4 ounces and measures about 3-l/4 x l-3/4 x 3/4 -- or smaller than a pack of cigarettes. The prosthesis is suspended by means of a cuff on the upper arm.
In brief, this prosthesis consists of three electrodes, a transistor amplifier for reinforcing the myoelectrical potentials which actuate a small motor, which moves the thumb toward the four rigid fingers by means of reduction gears.
This bioelectric prosthesis is useful only with medium length or long below-elbow stumps. A bioelectrically controlled rotatory wrist joint has not been developed. Short above-elbow stumps or shoulder disarticulations cannot as yet be fitted according to this principle because myoelectric elbow joints are not available.
The present system of electropro-thesis has no feedback features, neither for finger position nor for grip strength.
The model demonstrated seemed to function with sufficient reliability. If, indeed the reliability of the Russian electroprosthesis proves superior to the Vaduz arm and the prosthesis developed by Kegel in Paris, this is, to a great extent (according to the German experts) due to its more primitive construction, which lacks certain functional features that are designed in the aforementioned prostheses but which are not altogether achieved even in those models.
A compromise is always necessary between the cosmetic and functional features of an artificial hand. The bioelectric hand looks good, but the rounded finger caps of the opposing three fingers were relatively unsatisfactory for working purposes since a firm grip was not possible.
The simplicity of the construction of the Russian hand, limited to moderate hand opening and closure speeds and an almost constant grip force, insures minimum mechanical breakdown. However, the gripping strength of the electrohand was only about one-fifth that of the German pneumatic prosthesis.
Comparison of Russian Bioelectric Hand and German Pneumatic Hand
The German experts felt that the most significant method of evaluating the Russian bioelectric prosthesis would be to compare it with the German pneumatic prosthesis, developed at the Orthopedic University Hospital in Heidelberg after World War II.
The contact pressure of the electrodes used with the Russian hand was about half as strong as that required by the pneumatic valves of the German prosthesis which are mechanically controlled by muscle tension.
The pneumatic prosthesis which is used in Germany for all amputation levels gives the amputee a sense of feedback since the gripping power is proportional to the muscle tension applied to the valves.
The exercises used in training amputees to use the electrodes are exactly the same as those practiced in the training for pneumatic valve control by means of muscle tensing; the problem of faulty control caused by involuntary associated motion of these muscle groups during arm movement under load are similar in both.
As is apparent from the features listed in the Table 1 , the bioelectric prosthesis, although cosmetically acceptable, was very poor functionally. Furthermore, experience has shown chat the number of externally powered prostheses used is limited since they are generally not worn by unilateral amputees. For bilateral below-elbow and above-elbow amputees, however, the technically flawless German pneumatic prosthesis has proved its value for many years, according to the Delegation of German prosthetic specialists.
Outcome of Visit
During the final negotiations with the Lizensintorg firm in which the Russian representative, Director of the U.S.S.R. Trade Office in the Federal Republic, Engineer, W. Trebenko, also took part, the Lizensintorg people presented a contract proposal and implied that after the German Delegation read it, they were prepared for further negotiations.
The Germans emphasized that their highly developed pneumatic prosthesis had a strong trading value, which should not be underestimated; they also repeated their offer to permit Russian experts to visit at any time the orthopedic workshops and clinics in Munich and Heidelberg.