Research Studies at CAPP

Editor's Note: The following excerpts are reprinted by permission from the Eleventh Annual Report, 1965, of the Child Amputee Prosthetics Project, Rehabilitation Center, University of California, Los Angeles. Further information concerning the items presented or on other aspects of the CAPP program may be obtained from Milo B. Brooks, M.D., Medical Director.

The research and training experience of the Project staff indicates that the infant with an upper-extremity amputation can be successfully fitted with a prosthesis when he has achieved a stable sitting position. The advantages of early fitting, which have already been discussed in previous CAPP publications, may be summarized briefly as follows:

  1. The child with an upper-extremity deficiency appears to develop an easier and more normal two-handed pattern when he has a functioning prosthesis to assist him, and these two-handed activity patterns are practised at more nearly the same age as the intact child learns them.

  2. Without a prosthesis, the infant amputee tends to develop substitution patterns; he holds objects in the axilla or elbow bend, and works in an awkward and energy-consuming position. Also, there are many activities which the child simply avoids if he does not have the assistant extremity.

  3. The remaining normal musculature of the deficient limb depends on use for its development and growth. Although linear growth does not appear to be affected by prosthesis wearing, circumferential growth is markedly improved by use.

  4. A prosthesis assists the young child with severe involvements to attain an increasingly stable sitting balance, and in standing and walking. Children with a missing upper extremity do have trouble in learning to stand, and are delayed in attaining secure standing balance and in learning to walk.

  5. The limb-deficient toddler with a prosthesis appears to feel more "whole," for he demonstrates an ability to function more normally.

However, it is undeniable that the upper-extremity prostheses presently being fitted to limb-deficient infants and young children have some serious disadvantages; they are still essentially scaled-down models of adult prostheses (which in themselves are far from ideal), and in general the devices available for infant fitting are not yet adequate to completely fulfill the very specific needs of the young child. For example:

  1. The infant passive arm often weighs eight ounces or more, and as the major amount of this weight is at the distal end of the prosthesis, the problems of control and manipulation may be increased .

  2. The activities of very young children consist primarily of gross movements, and in order to keep the prosthesis on, extra straps are often required, thus constricting the child more than is desirable.

  3. An infant at the crawling stage subjects the prosthesis to unusual forces and strain. Prosthetists who have had little or no experience with children of this age group often find this a major fitting problem.

  4. Fitting the infant prosthetic arm is particularly difficult; for example, it must be aligned so that it will not be too much externally or internally rotated. Also, in the case of the below-elbow amputee, the short, rounded, and pudgy stump has a tendency to pop out of the socket when the child flexes his forearm.

A Unitized Arm for Infant Below-Elbow Amputees

Note that this is an experimental device only, that the design has not yet been finalized, and that consequently the item is not ready for quantity production.

In spite of these drawbacks, a well-constructed and fitted infant prosthesis does function; however, it was postulated that an in-depth design study might result in a prosthetic device with the following desirable characteristics:

  1. An infant unit arm which could be assembled from prefabricated components of a standardized design. There would appear to be several advantages to this plan; for example, the use of such components would result in a great saving of time--a factor which can be of particular importance to the commercial prosthetist. Also, standardized components could be replaced more quickly and easily, and would be less expensive. They could also be produced in some volume, permitting the utilization of quality control techniques, which could result in a more satisfactory product.

  2. The optimum combination of function and cosmesis. It was felt that the great variety of new plastic materials offered an interesting field for investigation, and some of these are now being evaluated.

A study was initiated for the purpose of developing an infant prosthesis which would fulfill the following essential criteria: a) a very lightweight unit; b) improved function; c) greatly simplified components; d) a design permitting prefabrication of components, utilizing good quality control; e) use of inexpensive materials of good durability and improved cosmetic characteristics; and, f) components which would require minimal time for assembly, replacement, or repair.

The components illustrated in Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 show the present status of this design study. A number of different materials have been used experimentally for the various components and are still being evaluated. Developmental studies are being conducted to determine the validity of the concepts we have proposed. This unitized arm is now being tested on a group of CAPP patients .


The terminal device (Fig. 2 ) is made of a very strong, lightweight plastic. It was designed to be used on either a right or left prosthesis (this will decrease the cost of manufacture and simplify the problem of replacement). This terminal device consists of a convex dorsal segment with a cupped inner surface; the distal portion of the outer surface is covered with a textured, slightly resilient cushioning material, and the palmar surface is filled with the same material. The thumb is a thin, curved plastic piece sheathed with rubber tubing. The prehension force is provided by a piece of rubber tubing which circles the thumb segment proximally and is secured by a spoke on the palmar surface of the shell.

Although the thumb and dorsal segment meet at the tip, their curvatures provide a space proximally, allowing the infant to shove small objects into this space, or use the fingers of the normal hand to open the terminal device to accommodate larger objects.

The amount of rubber-band loading is minimal because of the large

surface areas provided by the dorsal segment, and also because of the resiliency and texture of the material which fills the cupped palmar surface. The two segments were specially contoured in an attempt to achieve the best possible prehension, and the very narrow thumb increases the child's ability to view the object being held.

The Wrist Unit is a tapered, threaded cylinder of nylon which is secured inside the distal end of the hollow forearm section.

The Socket (Fig. 3 ) is made of a thin, transparent, and very strong plastic which is available in cylindrical tubing. Proximally it is formed over the stump mold, and continued distally in its hollow cylindrical form to become the core of the forearm section. The socket is preflexed to prevent stump pop-out for the short-below-elbow patient. The optimal number of degrees of flexion is still under study.

The forearm portion of the socket is sheathed with a sleeve of foam material (Fig. 4 ), shaped to approximate the desired forearm contour. A gauntlet of soft, resilient, flesh-toned plastic is then slipped over the forearm sleeve.

The Cuff is made of polyethylene, and so designed that the basic pattern can be used for either right or left prostheses. It is adjustable for size by placement of a simple snap fastener. A dacron loop is snapped onto the medial side of the cuff to hold the axilla cord of the harness. The cuff is secured to the socket with two rivets.

Patients with a short stump are fitted with a full cuff, whereas those children with long stumps may require only a nylon cord secured with a dacron keeper for adequate suspension of the prosthesis.

A Harness for Unitized Arm

This specially designed harness consists of a length of half-inch dacron webbing which forms a simple chest strap harness with one snap in the front, an over-shoulder strap on the prosthesis side, and a nylon cord running under the axilla on the prosthesis side and through a loop on the cuff (Fig. 5 and Fig. 6 ).

Resistance to the downward pull of the prosthesis is provided by the over-shoulder strap. The tightness of this strap therefore is critical in keeping the prosthesis on the child. The chest strap need not be extremely tight; when properly fitted it may appear tight, due to the plump contours of the infant, but it should be left loose enough to slip two or three fingers under it.

Minimal restriction to arm motion is provided by this harness (Fig. 7 ) since its only attachment to the prosthesis is by the nylon cord which slides through the loop on the medial side of the cuff, allowing the prosthesis to glide smoothly along this cord for forward and backward motions, and offering no resistance to abduction motions. The problem of external or internal rotation of the arm is minimized; the slipping of the front support strap over the shoulder is also eliminated. This problem, seen so frequently in the plump, rounded infant, was usually solved by the addition of a chest strap not needed in this design. The problem of axilla pressure, so often encountered with the figure-of-eight harness, is also eliminated.

Present Status of Unitized Arm Study

Six infant patients have been fitted with the unitized arm, and their progress will be followed by a prosthetist-therapist team until they are ready for an active terminal device (at approximately two years of age). These children are seen monthly by the team, and detailed evaluations of functional performance and mechanical factors, such as maintenance, are being recorded.

The weight of this unitized arm is approximately four ounces--which is about half the weight of the conventional infant passive prosthesis. The appreciably lighter weight of the entire arm appears to be an advantage from the first hour of wearing; for example, in the way the arm is carried and its spontaneous inclusion in the infant's activities.

So far there has been only limited opportunity to evaluate the terminal device in relation to its functional design criteria, since all of these infants are only slightly over one year of age at present. In gross activities such as crawling, leaning, sitting, and in gross grasp, it does appear to fulfill the functional requirements most satisfactorily.

The combination of this preflexed socket and new harness appears to have averted the problem of stump pop-out. No socket adjustments have yet been needed, and in this respect the anticipated advantages of a transparent socket are still untested.

The resilient foam sleeve and the textured gauntlet on the forearm appear to provide a considerable functional advantage in gross activities such as crawling, holding down objects, and clasping large objects between the two arms. The harness appears to be comfortable and highly functional for all of the infants in the group. It eliminates almost all the problems of the figure-of-eight for the infant, and provides excellent suspension and stability, with only minimal restriction of the child's arm movements. Also, because the chest strap can be relatively loose, it requires adjustment less frequently than the figure-of-eight .

Cosmetically, the unitized arm has been very successful. The families of all the children fitted so far have been very pleased with its appearance.

Terminal Device Studies

The terminal device previously described and illustrated is only one of several new designs which are presently being evaluated. A few of the others can be seen in and Fig. 9 , and are examples of our efforts to achieve the optimal combination of function and cosmesis.

Electric Cart for Multilateral Amputees

One prototype of an electric cart designed to provide mobility for patients with severe multiple deficiencies was described in detail in the CAPP Tenth Annual Report (1965, pp. 1-10). Briefly, this device is a compact and portable power-driven cart with a cushioned seat which can be raised and lowered by means of a power-driven lifting mechanism. The cart is operated by means of an electronic control system which the patient can manipulate with a phocomelic extremity--or with his chin, if necessary.

Prototype III, illustrated in Fig. 10 and Fig. 11 , is the most recent >model of this cart, and incorporates a number of changes in the previous design. (NOTE: This newest model was photographed prior to the addition of the chassis sheath, seat cushion, and backrest, in order to illustrate more clearly the mechanical changes)

Prototype III is approximately 15 pounds lighter than the previous model, which weighed 91 1/2 pounds. This weight reduction was achieved in a number of ways: the frame is now of #4130 chromium-molybdenum alloy of 5/8" 0.D. and .035 wall thickness. The rear wheels are unchanged, but the front wheels are a new lightweight type from Everest-Jennings (representing a weight reduction of 2 pounds 4 ounces).

The design of the seat platform has been completely revised, resulting in a weight reduction and a better folding arrangement. Also, extension locks have been added to the new model. The arrangement of the power system for the lifting mechanism has been changed; the two rear jacks are now connected by chain and sprocket, and the flexible drive shaft has been eliminated; the front screw jack is now connected by means of two universal joints. This new design has appreciably increased the efficiency of the system.

The drive motors are the same (12-volt, 5-ampere FoMoCo Seat Motors); however, the motor which powers the seat-lifting mechanism, and which was originally a 12-volt, 6.5 ampere FoMoCo Window Motor, has been replaced by one identical to the drive motors. All three motors are now positioned in the back, for accessibility, and the entire motor section now can be removed as one unit for easy servicing.

In this model the battery can be easily removed from the side. (By "splitting the weight" in this manner, the device becomes much easier to transport.)

The gear reduction unit has been changed from a jack-shaft unit to a worm and gear box reduction unit. The speed is now about 4 1/2 mph. (It was decided that the 7 mph speed of the previous model was excessive.) This change to a gear box was made in order to obtain some braking, and for the added advantage of being able to disengage the clutch and thus make the cart easier to push about. A V-belt is used to engage the motor. A more sophisticated braking system may be advisable, but the designers have been cautious about overdesigning.

The basic design of the control system has proved to be most satisfactory; no major changes were made, although the components were rearranged to make it more compact. The same type of aluminum sheath (.040 Alclad 2024-0 aluminum) has been used. A Hammertone finish has been used on the new model.

In redesigning the previous model, the objectives were to a-chieve lighter weight, a simplified design, and increased function with easier servicing. This has been accomplished, and Prototype III of this design is now ready for production. It is anticipated that a local manufacturer will produce this device commercially.

Quick-Change Wrist Unit

The quick-change wrist unit illustrated at right (Fig. 12 ), which has been described previously (CAPP Tenth Annual Report, p. 13), has undergone extensive and further minor design changes. The design of this unit has now been finalized and commercial production by a local manufacturer will begin in the immediate future.

A number of our patients are now using this unit. They are all unilateral amputees, and there are both above-elbow and below-elbow deficiencies in this group. These patients are between the ages of ten and twenty-one, and each has more than one terminal device. They have all reported favorably on the convenience and ease of operation of the unit. Pop-out and replacement are very reliable, and the rotational adjustment is very smooth. Perhaps the biggest advantage of this unit is that it permits the wearer to select a specific amount of friction for each terminal device. The frictional adjustment is on the hook adapter, therefore the wrist unit does not require readjustment each time the hook is changed. None of these patients has yet required any repairs on the unit.