Experience with Carbon-Dioxide-Power-Assisted Prostheses

CONSTANCE LUNDBERG, OTR SIEGFRIED W. PAUL, C.P.O. EARL E. VanDERWERKER, M.D. JOHN C ALLEN, M.D. Children's Hospital Newington, Connecticut


Experience with bilateral upper-limb amelia, bilateral very-short-above-elbow deficiencies, and phocomelia at the Newington Children's Hospital Prosthetic Clinic had been exceedingly discouraging until the introduction of externally powered prosthetic equipment. Conventional equipment had proven to be too heavy and clumsy, with too much effort required to permit effective use, and usually an inadequate number of body motors was available to power the various components. Moreover, excessive occlusion of body surface interfered with heat loss in warm weather. We had had experience with the Grand Rapids feeder arm which assisted in the function of eating, but did not provide any particular advantage for other functions, and maintenance was prohibitive. It was because of these features that we sought out the carbon-dioxide-powered prosthesis developed at Heidelberg University. Although our experience, as shown by the table below, has not been extensive, it has been most instructive.

Experience with the C02-Power-Assisted Prostheses

Prostheses delivered

9

Prostheses on order

2

Prostheses awaiting authorization

2

Total

13

Types of Deficiencies and Number of Patients Fitted or in Process

Acquired shoulder disarticulation*

3

Bilateral amelia

3

Phocomelia

1

Terminal transverse(humeral) hemimelia

2

Total patients

9

Use Experience

Six patients have received power-assisted arms and all but one use their equipment. Prostheses were rejected by one of the patients with bilateral short-above-elbow loss (humeral hemimelia).

The Heidelberg Systems

Somewhat over 20 years ago Haefner and Marquardt developed auxiliary-powered upper-limb equipment at the Heidelberg University Prosthetic

*One of tumor etiology, one resulting from shoulder avulsion, and one an extremely short-above-elbow stump with minimal bone in soft tissue which necessitated fitting as a shoulder disarticulation.

Clinic in Germany. Today the improved Heidelberg systems now in use are, in our opinion, the most effective of those available for patients who have insufficient body power to operate a conventional prosthesis. In these systems, pneumatic power provides grasp control, full wrist rotation, and full elbow motion. Ease of application, durability, and low maintenance costs make this equipment uniquely suited to meet the problems of the severely impaired child. Patient age and the level of anatomic deficiency determine the specific components of the prosthesis. All parts are prefabricated, and the considerable variety available allows for individual adaptation very nicely.

Equipment Used

We have used the utility hook, as well as a functional hand, together with a full range of powered motion at the wrist. The use of an automatically locking wrist has provided steadiness in holding heavy objects. The powered elbow joint provides flexion, and gravity effectively establishes extension. A powered locking mechanism is provided at the elbow joint, and a passive turntable is available for positioning the arm. The humeral section consists of a plastic cover over a metal bar which connects the shoulder and elbow joints. The shoulder joint provides passive abduction, and humeral rotation is controlled by friction. An open frame at the shoulder joint provides room for movement of the patient's pectoral girdle to operate the control valves inside the prosthetic socket. The socket is made of a thermoplastic (Vitrathene), and is designed to provide suspension and to distribute weight over a wide area of the body (Fig. 1 and Fig. 2 ). The socket has windows, in areas where support is not needed, to assist in heat dissipation as well as to allow sufficient shoulder excursion to control the valves. Two types of valves are commonly used in this equipment. One is a two-way valve for hook or hand control, and the other is a four-way valve for the wrist and elbow which includes the activating mechanism as well as a locking mechanism to maintain a desired position.

Power Source

The source of power is carbon dioxide under pressure in a stainless-steel bottle, as required by law in this country. This bottle lasts from six to eight hours with average use and. with a spare bottle which can be easily interchanged, the supply in the two containers is more than enough for a very active day. The small CO 2 , bottles are easily recharged from a large siphon lank which is available for home use at a cost of approximately $7 a year. Pressure inside the bottle is 27.2 Kg/cm 2 (387 lb./in. 2 ), and a pressure-reducing valve is used to provide a 6.8 Kg/cm2 (97 lb./in. 2 ) exit pressure for operating the prosthesis (Fig. 3 ).

Fabrication

Measurements, casting, and assembly of components for fabrication of the prostheses are quite routine for any skilled prosthetist. Locating the control valves, fitting the socket, and providing effective, comfortable suspension can be delicate operations at times. The use of Velcro straps for closure makes application easier. Particular attention has to be paid to the clavicle and the spine of the scapula, especially in relation to movement of the pectoral girdle within the shoulder socket. Usually the various surfaces of the acromion are used to activate, by pressure, the control valves. Permanent location of the valves is determined after temporary mountings during the training period. Sometimes several repositioning moves are required.

Locating the valves so that opening and closing the hook or hand can be achieved by a forward motion of the shoulder to depress the valve is apparently most appropriate, and is easily taught. Raising or elevating the shoulder has been used to activate elbow flexion and extension. Moving the acromion posteriorly to apply pressure on the control valve seems to be a most effective way of controlling supination and pronation of the wrist.

Valve Operation

Slight pressure on the valve activates a function, such as opening the hook, positively. Function will stop as soon as the patient ceases to depress the valve, which is spring-loaded. Complete depression of the valve activates the reverse motion by deflating the particular system. The spring loading of the hook or hand, or the wrist, will then bring the device to its preactivated position. Similarly, the elbow is extended by gravity, the extent being governed by the amount of gas released from the system. With the system completely deflated, the various components are spring-controlled, and the hook is open, the wrist is pronated, and the elbow is fully extended.

Training

The goal in training children in the use of C0 2 -powered prostheses is, of course, to obtain the highest possible level of independent function. To accomplish this purpose all available assets must be used. In bilateral amelia, for example, this means that the manipulative abilities of the feet be used to supplement the grasp and release capabilities of the prostheses.

Anticipated daily-life situations should be explored to find the most efficient and practical solutions. The child's ability to generalize instructions and solve problems on his own is a definite consideration in fitting the very young child. If this ability has not been developed, the introduction of such equipment probably is contraindicated at that time.

The use of a Velcro strap and D-ring arrangement provides a very satisfactory substitute or replacement for a buckle since this method of fastening can be manipulated by the toes. If the socket is split so that it opens in the back, as well as in front, the patient can apply it himself. Use of the feet by a patient is vitally important and needs to be developed, if it isn't already available, so that combined use of the feet and the prosthetic equipment is possible. Use of the feet, at least to the level of the chest, with sufficient strength to fasten straps securely, should be cultivated during training.

Since no active shoulder abduction or flexion is present, or any internal rotation, the patient's ability to utilize his prostheses in bilateral activities or in midline functions is extremely limited there being no wrist-flexion units available for use with the Heidelberg system. Therefore, total dressing is not possible. A child can be taught to put a front-buttoning shirt over his prosthetic arms before he puts them on, and then use a buttonhook with his feet, but two-handed manipulation is not possible. Independent feeding is possible if a swivel spoon or a fork is used. Bringing food to the mouth is done by spearing the food, and then getting it to the mouth with elbow flexion and supination. The table used should be slightly below elbow level, and, since no active shoulder flexion is available, a cut-out table is of considerable assistance. A straw is more practical for drinking than is lifting a glass to the mouth because of the weight of the liquid and the poor angle for pouring.

The prehension of the powered terminal device cannot be graded as finely as that of a standard voluntary hook. Consequently, there is a very real tendency to squeeze soft food, such as sandwiches.

Proper configuration of the forearm piece is necessary to avoid impingement at full flexion.

We have encouraged use of the prosthesis for writing signatures since this skill is needed in public areas. Writing with the toes, however, is usually much easier and quicker and can be done at home and in school without problems.

Obstacles Overcome

Early in our experience, obstacles were encountered in the performance of everyday activities, due to lack of shoulder flexion and shoulder mobility. These deficiencies prevented youngsters from reaching objects which are at waist height for adults, such as doorknobs, sinks, and tabletops. With increased height through growth, these problems become less significant but are a major factor in the fitting of a child of five or six years of age, or any person of short stature.

As with any procedure or mechanism, there are limitations and contraindications to the use of CO2-powered prostheses. Age is a limitation in that it is an indication of developmental level. The successful use of C0 2 requires problem-solving ability on the part of the patient in that he must be able to generalize instructions in the use of valve mechanisms. In our experience, a child generally needs to be six years of age or older in order to have this ability. While we have tried the equipment with children as young as four years of age, the extensive training required and the mediocre results obtained were discouraging.

On occasion a very minimal "hissing" sound is associated with the operation of the C02-powered equipment. The noise level has not been objectionable to any of our patients. The speed of operation of the various components has also been quite acceptable. Only when the gas bottle is about exhausted is the motor objectionably slow.

Frustration arising from previous negative experiences with ineffective prostheses often results in hard-to-control behavior and rejection of a new system, even before it has been tried extensively. This behavior requires the active realistic support of the family and those working with such a person in order to overcome his negative reactions.

Facilities for servicing C0 2 equipment should be reasonably available. When this sophisticated equipment gets out of order, it requires more than the services of an interested mechanic. If the prosthetic shop is more than a day's travel from the patient, the practicality of the prosthesis is easily lost (Fig. 4 and Fig. 5 ).

Conclusion

This prosthesis has considerable value in that it allows some functions to be accomplished in a socially acceptable manner. In our opinion it is the best system thus far available and has been shown to be stable. Further development in some areas is desirable. Internal rotation and abduction at the shoulder would go far in permitting manipulation and activities at the midline. More universal use of the prostheses without the very careful control of the height of the table or other working surfaces would also be possible. Just recently we have developed a shoulder joint which places the arm in mild abduction and provides a limited range of active flexion.

The feet can be of major importance in manipulation, and in combined use with the prosthetic equipment. They should not be so dressed or managed medically or surgically as to exclude them or their mobility.