A Comparison Of Two Infant Terminal Devices

Julie Shaperman, O.T.R.

The shift from the previously accepted prescription of mitten terminal devices to appropriately sized functional hooks in the initial fitting of infants required careful evaluation of pertinent factors before it became standard procedure in our clinic. When data sources are as variable and mercurial as growing infants, collection of significant clinical material is a time-consuming, difficult task.

Mrs. Shaperman, assisted by Miss Jeannine Dennis, O.T.R., delighted the members of our staff with this interesting, carefully prepared study. I am confident that physicians, therapists, prosthetists, and social workers concerned with the child amputee will find the project to be of equal interest and am also certain that it will help them to develop valuable criteria in the continued improvement of infant fitting and technique. Mrs. Shaperman's report follows:

Cameron B. Hall, M.D.
Orthopedic Consultant
Child Amputee Prosthetics Project
University of California at Los Angeles

Prosthetic fitting of infant upper-extremity amputees under two years of age has become a well-accepted procedure at many clinics. At the Child Amputee Prosthetics Project (CAPP), attainment of sitting balance is the criterion used to determine the proper time for application of the prosthesis. However, clinicians have not yet reached complete agreement as to which terminal device is best for the upper-extremity amputee under the age of two years.

To test the hypothesis that the small plastic-covered hook (Dorrance 12-P) is superior to the Infant Passive Hand, or Mitt, a long-term study was conducted at CAPP. Two groups of infants, all with below-elbow amputations, participated in the study. The evaluative criteria applied were: 1) function for gross and fine prehension activities usually performed by infants; 2) motor development; 3) subsequent learning of cable control; 4) maintenance requirements; 5) safety, and 6) acceptance.

The study began five-and-a-half years ago and included observations of 20 below-elbow infant amputees fitted with the Mitt, and 22 infants with similar amputations who were fitted with the Dorrance 12-P hook (Fig. 1 ). From this group of 42 patients, 16 cases were selected to provide two groups matched as closely as possible for purposes of detailed comparisons. The matched sample appears in Table 1 .

Method of Evaluation

Detailed notes on the two groups of patients were made by the physician in connection with periodic physical examinations, by the social worker in the course of interviews with parents, and by the psychologist during the administration of intelligence tests.

The child's performance was observed at regular intervals by the therapist and the findings recorded on a specially prepared Functional Evaluation Form.* Films of each child were reviewed and rated on a prepared scale. The infants who wore the 12-P hook were not initially fitted with a control cable. When the children in both groups met certain readiness criteria,1 they were provided with a Dorrance 10-P or 10-X hook with cable; this usually occurred at about the age of two years. Data on the speed with which operation of the cable-controlled hook was learned was recorded by the therapist, together with the quality of the learning.


The following results were observed:

1. Function: The 12-P hook and the Mitt were equally effective in the two-handed gross grasp of large objects; and for stabilizing objects on a surface and against the body. The hook was found to be superior, however, for holding small objects; the cleft of the Mitt was too large for pull-toy strings, but not large enough for most toys themselves. Even with small objects wedged into it, the holding power of the Mitt was most unreliable. However, objects placed in the hook were held with good stability.

Comparison of the Mitt and the hook for stabilizing the infant in sitting balance, crawling (Fig. 2 and Fig. 3 ), "pulling to stand", and "standing supported" showed that the Mitt and hook were equally effective for all except "pulling to stand", in which the hook was superior. By hooking the curvature of the fingers over objects, some children could obtain assistance in pulling themselves up.

2A. Learning: Awareness of Prehension. Children who had previously worn the 12-P hook (Fig. 5 ) learned to operate the cable-controlled hook faster and more easily than those who had previously worn the Mitt (Fig. 4 ). It was noted that before the age of eighteen months none of the hook wearers (Fig. 5 ) had developed tolerance for objects placed into the hook, but pulled them out. Some did not develop this tolerance until they were nearly two years old, and some even later. However, they did become accustomed to seeing objects held in the hook, and gradually most of them began to ask to have objects placed in the device, or to have the hook opened for them, or try to open it themselves in order to place an object in it.

This level of development was regarded as one of the criteria for adding the cable. When the cable was added, the children had to learn how to open the hook, but did not need to be told its use; they already knew that the hook was a holder of objects.

2B. Speed of Learning: The majority of the infants who had worn the hook from the start demonstrated a fair degree of ability to open it during the training session given the same day the cable was installed. Even those who required longer training periods to learn the technique of hook opening were highly motivated by knowing the purpose of the opening.

The majority of the children who had worn the Mitt (Fig. 4 and Fig. 6 ) required a longer time to grasp the concept of opening the hook by flexion of the humerus. About half of the Mitt wearers demonstrated some ability to open the hook by the end of the first week of training, but others required a considerably longer period of time to learn the technique, and even when they did learn, some did not know why they had opened the hook. The hook was a new and strange device to them, and they needed a great deal of encouragement to place objects into it. Many continued to cradle objects against, their bodies for months after learning hook operation.

2C. Improvement in Skill: The rate of improvement in hook operation skill was only slightly slower for former Mitt wearers than for former 12-P hook wearers. The former Mitt wearers (Fig. 4 and Fig. 6 ) required much direction and motivation to employ the hook's prehension function. However, once a pattern of prehension function had been developed, it was difficult to tell which of two children had originally worn the Mitt and which the hook.

When a cable was added, the former 12-P hook wearers retained, of course, the same shape and type of terminal device, and appeared to quickly and easily integrate hook operation into their natural patterns of body movement. They rapidly developed a very natural-appearing two-handed prehensile awareness. The advantage of the hook was in the speed of development of the prehension pattern and in the greater ease and motivation it provided for learning cable operation.

3. Maintenance: Approximately the same number of terminal device replacements were required with the 12-P hook due to soiled or torn plastic as were required with the Mitt because of soiled or torn gloves. Width, length, and friction factors were approximately equal. The hook was one ounce heavier than the Mitt, but appeared to be well within the limits of the infants' ability to lift and manipulate easily.

4. Safety: Initially, the hook presented a slightly greater safety hazard to children than did the Mitt. However, few children dealt themselves any blows with it after the first few days, and those that did occur were minor. Only one injury to furniture was reported. In a few instances, the child attempted to use the hook as a weapon against another child, but again no serious consequences resulted. The aggressive activity was not repeated after the parents admonished the child not to hit with the hook, just as they should not hit others with their sound hand. Parents of children wearing the Mitt also reported a few minor injuries.

5. Acceptance: Acceptance of the small hook was good, as was acceptance of the Mitt. Since parents were not given a choice of terminal device for the infant, acceptance was closely related to acceptance of the prosthesis as a whole. Differences, however, occurred at the time of the change of devices. Parents of Mitt wearers were told at the time of the initial fitting that the child would receive a hook with cable when he was ready for active grasp, but several families resisted the change. They considered the Mitt to be more cosmetic than the hook, and considerable effort was required on the part of the physician and social worker to convince them of the functional benefit the change would offer their child. Parents of the 12-P hook wearers regarded the change from the small hook to the larger one with cable as a "promotion" for their child, and many asked to have the cable added before the staff felt that the child was mature enough to participate in a training program.

Since completion of the study the belief of our staff in the functional benefits of the 12-P hook has provided an important supportive effect on families' acceptance of the hook.

Additional Observations

Although this study was confined to unilateral below-elbow amputees, clinical findings indicate that the 12-P hook is a useful and appropriate terminal device for other infant amputees. This was noted especially with bilateral upper-extremity amputees, as their need for prehension is more acute and more closely related to the basic self-care needs than is the case with unilateral amputees. It was also noted that their need for the change to a larger hook usually occurs sooner than for children with unilateral amputations.


The results obtained in this study appear to indicate that the 12-P hook is the preferable terminal device for the infant amputee. The slight increase in injury hazards during the first few days is not considered a deterrent to its use. The 12-P hook provides increased function for holding small objects, aids in "pulling to stand", facilitates later learning of cable control, and eliminates acceptance problems when the terminal devices are changed. It is also equal to the Mitt for gross holding functions and motor development; and requires no greater maintenance.

During the course of this study, the CAPP staff became so impressed with the effectiveness of the 12-P hook that it is now the only terminal device used for infant upper-extremity amputees at our Project. It should be pointed out, however, that although the 12-P hook appears to be currently the best device available for the infant amputee, the development of improved terminal devices for these patients is still greatly needed.

* Information available from CAPP on request.

Julie Shaperman is with the Child Amputee Prosthetics Project, University of California at Los Angeles