An Electrically Powered Elbow Unit

Robert E. Tooms, M.D. Ronney Snell, CP. Elizabeth Speltz, R.P.T.


A great deal of interest has been generated by the use of external power-both electricity and compressed carbon dioxide gas-in prosthetic devices. For the severely handicapped amputee, several centers have developed prostheses that are totally powered by one or the other of these sources of energy. There are, however, a number of amputees now using conventional prostheses who could be greatly benefited by external power, even if its use were limited to providing assistance in the performance of one or two prosthetic functions, such as elbow control or terminal device operation. We would like to relate our experiences with an electrically powered elbow unit fitted to one such patient.

K.S. is an 11-year-old boy with congenital limb deficiencies of both upper extremities. Functionally he is a bilateral shoulder disarticulation amputee, having a complete amelia on the left and a phocomelia on the right (Fig. 1 ). The phocomelic limb has very minimal active function. K.S. was initially seen in our clinic in 195 6 at the age of one month. When he was two years old he was fitted with a left shoulder disarticulation prosthesis with a passive elbow and a wafer hook. Four months later a right shoulder cap was applied. One year after initial fitting, the terminal device was activated via a perineal control strap and the elbow lock activated via a mouth-controlled pull strap. Despite intensive training the patient was not able to use his prosthesis with any degree of effectiveness at this time.

In November 1962, when K.S. was six years of age, he was fitted with new bilateral shoulder disarticulation prostheses. The terminal devices were activated by control straps attached to quadrilateral perineal cuffs, and the elbow locks were activated by chest straps controlled by trunk rotation. After further training sessions the boy developed satisfactory function with both of his prostheses. New prostheses were required in 1964, and at that time forearm lift assists were added.

From the time K.S. was fitted with bilateral shoulder disarticulation prostheses in 1962 until the present, he has been admitted to the Memphis Crippled Children's Hospital on five occasions for intensive training sessions. Prior to fitting with the electric elbow unit, he was able to feed himself with minimal assistance, using special utensils, and could attend to his toilet needs with some assistance. He was not able to dress himself without a great deal of help and could not, of course, don or doff his prostheses without help. However, he attended regular school, wrote well, and made good grades.

A muscle-strengthening exercise program for the phocomelic limb has been carried out since early childhood in hopes that this limb might eventually serve as a power source for activation of either the terminal device or the elbow lock. This utilization has been attempted on several occasions, but without success.

In December 1966, Jim Allen and Andy Karcheck, of the R&D Engineering Company of Downey, California, designed an electric elbow unit for this patient. The unit provides forearm flexion and extension via a small motor which drives a worm gear (Fig. 2 ). The power source is a rechargeable 12-volt nickel-cadmium battery which fits into a small leather case attached to both shoulder caps posteriorly and is well concealed by the patient's clothing (Fig. 3 ).

The power supply is more than adequate for a full day's operation, and the battery can be recharged overnight. The control switch is of the two-directional lever type and is mounted in the humeral section of the prosthesis, where it can be controlled by motion of the phocomelic limb (Fig. 4 ). All wiring has been covered with Teflon, which has a high melting point, so that in case of a short circuit the wire cannot come into contact with the patient's skin.

The entire unit is installed in a standard Hosmer E-200 elbow setup with the internal mechanism removed. This arrangement allows use of the regular elbow turntable and wrist friction unit. Since the need for an elbow lock is eliminated by the worm gear mechanism, the terminal device can be operated by a simple single-control Bowden cable attached to a perineal strap (Fig. 3 ), rather than by a dual-control system. With the increased mechanical efficiency of the single-control system, more rubber bands may be used on the terminal device to increase the prehension force.

K.S. was able to operate the elbow unit quite well as soon as he became familiar with the control switch and required no real training sessions. Since its installation, he performs such activities as feeding, mouth hygiene, toileting, and dressing much more rapidly, dexterously, and effortlessly than before. Frustration has been minimized in performing certain tasks. He still requires considerable help in dressing and cannot don or doff his prostheses alone.

At the time of this writing, the electric elbow unit has been in daily use for over six months. Maintenance has been limited to minor problems with breakage of small wires on the external portion of the prosthesis. This difficulty was easily solved simply by relocating these wires. No problems have developed with the motor or the batteries. Operational noise of the motor is minimal and not objectionable.

K.S. has been very pleased with the elbow unit and has demonstrated a great deal of pride in his increased accomplishments since its installation. We feel that the unit has been of unquestionable benefit to this patient and could have widespread use in helping other children with similar severe disabilities .

Robert E. Tooms, M.D., Ronney Snell, CP. and Elizabeth Speltz, R.P.T. are associated with the Child Amputee Clinic Crippled Children's Hospital Memphis, Tennessee