An Externally Powered Prosthesis for Unilateral Congenital Amelia

JAMES HUNTER, M.D. JOHN BENNER, M.D. JAMES SWEIGART, C.P.O. MARGERET HOWISON, O.T.


Summary

The majority of discussions of prosthetics for upper-limb amelia presented in the literature deal with bilateral cases and the many technical difficulties in developing functional prostheses for these children. In this article we present a case report describing an externally powered prosthesis for unilateral upper amelia, and the technical difficulties unique to unilateral cases as well as those shared with bilateral cases. The Michigan electric hook has been used as the basis of a lightweight prosthesis which has provided improved function and has achieved greater acceptance by the patient.

Case Presentation

B.B. is an 11-year-old female who was first presented to our clinic at age 3 for treatment of right upper amelia. Physical examination at that time revealed complete absence of the right arm and shoulder girdle with the exception of a small segment of proximal clavicle ( Figure 1 and Figure 2 ). The patient was initially treated with a cosmetic shoulder-cap device which she readily accepted.

At the age of 7 years the patient was fitted with a conventional forequarter prosthesis with shoulder cap, a universal shoulder joint, Hosmer E-50 locking elbow, Hosmer flexion wrist unit, 99X hook, and excursion amplifier. There were several difficulties noted with this prosthesis. First, the prosthesis was heavy, causing it to slide down the patient's slender torso. Secondly, motor supply to the elbow and hook was difficult because of the inadequate excursion and power available. Even with the excursion amplifier, the prosthesis was nearly nonfunctional and was not used by the patient. With these difficulties in mind, fabrication of a lightweight forequarter prosthesis was undertaken. The components consisted of a plastic-laminated shoulder cap, a Hosmer SAJ-100 flexion-abduction shoulder joint (adult-size ground down), a Hosmer child-size E-50 positive-locking elbow (with a custom-made flexion assist), and a Hosmer nylon-body friction wrist No. 1412. The terminal device is an externally powered Michigan electric hook. The electric hook is controlled by a microswitch mounted in the shoulder cap, the switch being operated by the rudimentary clavicle. The sternocleidomastoid muscle provides the muscle motor for the clavicle. A nickle-cadmium battery is located in the left axilla to help balance the shoulder cap and arm ( Figure 3 and Figure 4 ).

The present prosthesis has several advantages over the previous conventional prosthesis: 1) the prosthesis is lighter, and a tighter fit has been obtained to eliminate movement, 2) addition of the electric hook has allowed the patient's scapular abduction to he used solely for tlexion of the elbow, 3) the rudimentary clavicle allows easy activation of the electric hook, and 4) the prosthesis has been readily accepted by the patient and is highly functional ( Figure 5 ).

The main difficulty with this system to date has been frequent technical failures in the electric hook, necessitating many repairs. These problems have been accepted by the patient, however, and hopefully with more research and development of the hook these difficulties will he overcome.

Discussion

With the occurrence of severe limb deficiencies in the thalidomide babies of the early 1960's, interest in prostheses for phocomelia and amelia heightened considerably. The fabrication of a light, functional, and cosmetically pleasing externally powered prosthesis for the upper limb was particularly desirable, especially for the patient with bilateral upper-limb amelia 9 . Several different designs were developed, including the Heidelberg pneumatic arm prosthesis 6 , prostheses with myoelectric control, and an electrically powered prosthesis 5,6,11 .

The technical difficulties in dealing with bilateral upper amelia are tremendous 3,6,7,10 . A few of the major problems are 1) lack of scapulohumeral movement to power the prosthesis, necessitating either external power or severe body contortions to create movement, 2) the absence of switch-activating sites for externally powered prostheses, 3) the lack of bony and soft-tissue anchors to hold the prosthesis in place, 4) the nearly total lack of sensory feedback to the patient, and 5) the need for complicated harnessing and power systems beyond the level of understanding of the young patient with amelia.

Patients with unilateral amelia present fewer technical difficulties but bring up several problems unique to unilateral upper amelia. Probably the greatest challenge in the unilateral patient is to create a prosthesis that is as functional and cosmetically pleasing as possible, so that the patient will accept it. Many patients with unilateral amputations reject the prosthesis entirely, preferring to use a passive prosthesis for purely cosmetic reasons. This is attributed to the fact that the average person can attend to most activities of daily living with one arm, and the functional use of a prosthesis is a skill which many amputees do not have the patience, intelligence, or motivation to learn 7 .

The first prosthesis designed for our patient was conventional and had the advantages of simplicity, reliability, relative freedom from maintenance, some sensory input, and durability. Several problems were present, however. These problems were apparent in the fact that the high-level amputee, who requires control of a greater number of movements, tends to have the fewest available body sites for harnessing a sufficient range of motion and power. In our case the shoulder-harness system was cumbersome; and, although the patient could obtain some force and excursion using the opposite scapula and humerus, the normal side was somewhat restricted and function was suboptimal and weak. Secondly, active elbow flexion and terminal-device operation were not possible simultaneously. Thirdly, it was difficult to keep the prosthesis in position because of the thin thorax and the lack of bony or soft-tissue prominences.

In designing the definitive prosthesis, it was decided that the patient should be supplied an externally powered terminal device, leaving her own limited resouces for elbow motion. The device decided upon was the Michigan external-power system for the Hosmer/Dorrance 10X and 10P hooks. The patient's small residual clavicle was used to activate a microswitch built into the prosthetic socket. The results obtained were pleasing to the physician, prosthetist, and patient. The prosthesis was light and cosmetically pleasing, simple to operate, and functional.

With the exception of mechanical difficulties with the electric hook, it has proved to be a satisfactory solution for the patient with unilateral upper-limb amelia.

Using her new prosthesis, B.B. has been able to do bilateral activities with less effort and more precision. She is now able to do activities which require shoulder stabilization while the "fingers" are operated electrically. She is able to maintain her limbs in a functional position within her line of vision. Of special interest to her is the new ability of cutting with scissors and turning the pages of a book while holding it. She has demonstrated the ability to hold and eat corn on the cob and watermelon and to do leather lacing ( Figure 6 , Figure 7 , Figure 8 , and Figure 9 ). As she is guided and as she independently experiments with new activities, she continues to explore new dimensions of function whieh previously were not available to her.

References:
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