Early Learning of Hook Operation

Julie Shaperman, MA., O.T.R.

In the past the Child Amputee Prosthetics Project at UCLA (CAPP) has conducted a number of studies to investigate the learning patterns of young children attempting to master the active operation of a terminal device. CAPP's current techniques for teaching this skill are based upon findings from these studies. In 1970, however, ICIB published an article by Trefler2 describing a different approach for teaching young children to operate a terminal device. In the method presented, a cable is added to the prosthesis when the child reaches the age of 15 months, and therapists instruct parents in ways to teach hook-operation skills at home. Since the new method's sequence of learning and its timing of instruction differ from those of our previous methods, a study was designed to investigate the new procedure.


The traditional CAPP approach is to add a cable to the prosthesis when the child shows readiness for learning to operate the terminal device-that is, when he can follow simple instructions, is interested in bimanual prehension activities, has a reasonable attention span, is willing to be handled, and is aware of the prehensile potential of the terminal device. Experience has shown that such readiness occurs shortly after the age of two years, and that children of that age have sufficient neuromuscular development to achieve a satisfactory level of control over the unit. When the cable is added, a therapist gives a period of instruction in its operation, with support from the parents.

Studies of two-year-old children fitted in this manner showed the following sequence for learning terminal-device operation:

  1. Maintain hook opening
  2. Initiate hook opening for grasp
  3. Relax and close hook
  4. Open hook for release.

This sequence has been observed in a large number of children1.

In another CAPP study3000 seventeen children had a cable on the prosthesis from the time of first fitting in infancy, and they received no training in hook operation. Three-fourths of them did not acquire the hook-operating skill spontaneously as part of their developmental progression, and the one-fourth who learned cable control probably had some instruction from parents at home. This study prompted a recommendation for a follow-up study in which parents would be instructed in ways of teaching hook operation while working with the children at home. It was suggested that this instruction begin when the child demonstrates manual hook opening, usually between 13 and 18 months of age. The Tretler article2 provided further impetus for this follow-up study.

In the proposed procedure, children are fitted with a cable at 15 months of age and are taught hook operation in the following sequence:

  1. Release objects
  2. Relax after object is placed in hook
  3. Reach for object to be placed in hook
  4. Place objects in hook himself
  5. Operate bimanually at body midline.

In this five-step method, the parents work with the 15-month-old child at home for brief periods, teaching the child to associate the word "open" with the arm movement needed to open the hook and drop an object which has been inserted into the hook. Parents return to the clinic weekly for four weeks and then monthly for checks with the therapist.

Procedure for the Study

Nine CAPP patients were fitted with a cable near the age of 15 months as proposed by Trefler. The children and parents attended four weekly therapy sessions immediately after addition of the cable. Parents were taught how to instruct children in hook operation at home, and families returned every four to six weeks thereafter for further instruction from the therapist. These visits continued until the child reached the age of two years. At follow-up sessions parents reported problems and progress as well as observations on skill development, and these were recorded by the therapist throughout the study period. If the child had not learned to operate the hook by age two but met the traditional readiness criteria for accepting instruction from a therapist, as described in the foregoing Background section, a regular training program was instituted. If the child was not ready for training, parents continued to work with him at home; and progress was reviewed periodically by the therapist.


The study was initiated with nine children. However, since one child left the area soon after the cable was added, data are included for only eight children. Seven CAPP patients had congenital unilateral terminal transverse partial hemimelia, below-elbow type, and one had an acquired transcarpal amputation; six were left and two were right. Six had short below-elbow deficiencies and two had wrist-disarticulation or transcarpal deficiencies. Four of the children were boys and four were girls; five were full-waking-hours wearers of the prosthesis and three had irregular wearing patterns. Average age of first fitting was 10 and 1/2 months, and average age at which the cable was added was l5 and 3/4 months. Actual ages for addition of the cable ranged from 14 and 1/2 months to 18 months because of family commitments and scheduling requirements (Table 1 ).

Three forms were devised for recording data. One listed basic identifying information for the patient and his prosthesis, another was a narrative sheet which was used to record information given by therapists and reports received from parents, and the third was used to record the child's skill level in detail at each visit. An addendum to this article contains a list of items which CAPP therapists included in their orientation sessions with parents.


All patients in the present study learned to open the hook to release objects, but none of the patients progressed beyond the second step in learning, and none of them learned to operate the terminal device well enough to make follow-up therapy unnecessary. By the time they reached the age of two years, two children had partial control of the terminal device; two were ready for additional training which, in essence, was identical to that given to children who have just received a cable at age two years; and four were still too negative to participate in any training program. The ages at which the children in this study attained excellent operating skill and spontaneous use of the prosthesis ranged from 28 to 37 months, with an average age of 32 months.

Sequence of Learning Observed in CAPP Patients

Step 1: Releasing an object from the terminal device. At the age of 15 months, children were guided through the body-control motion passively and then were encouraged to perform it actively. Children were expected to attend to the activity for only a brief time because of the rapid interest shifts of children at that age. In this CAPP study, all children learned to open the hook actively to drop objects.

At 15 to 16 months of age, the children used very gross body motions to open the hook. Some of the children bent forward at the waist, extended the elbow, and pushed the hook down toward the floor to get it open (Fig. 1 ). In the sitting position, they extended the elbow and pushed the arm down toward the toes or up overhead. One child imitated the passive body-control motion which her mother had used by taking her own sound hand and pushing her prosthesis forward (Fig. 2 ).

Step 2: Relaxing after an object is placed in the device. As soon as they had mastered the first step, the children were shown how to relax to hold an object placed into the hook. However, only one child in the study learned to do this. For most of the children, mastery of step one occurred at about the same time that they reached the developmental stage in which they wanted to run, climb, and be involved in gross active play. At that point their only independent hook-operation function was opening for release, and they had to rely on parents to place objects into the hook. They then became impatient and resistant to hook use, preferring gross play activities.

As the children reached the age period of 18 to 24 months, two other things occurred. First, they became resistant to handling by adults and would not allow parents or therapists to move the prosthesis in the body-control motion or touch the hook to place objects into it. As this resistance increased, the children seemed to forget the skills they had acquired prior to that time.

The second result was that four of the children found alternate ways to get the hook open independently to grasp objects. They opened the hook manually by pulling on the operating lever with the sound hand; then they took up enough cable slack to maintain the opening while they pushed an object into the hook. Since they could not control hook closing, this operation was successful only part of the time.

None of the children in this CAPP study learned steps three, four, or five until the age of 24 to 30 months. In the third year of life, when the child showed readiness to take instruction, training sessions were started to teach hook operation in the usual manner used at CA PP. The learning sequence observed at that time was similar to that seen in children who first receive a cable at two years of age. That is, primary interest was in hook opening for grasp of objects. At age two years, they were not interested in the game of "open" for release. Although all children had been able to open the hook actively for release at 15 months of age, all but one had forgotten this skill by age two. They required passive assistance to relearn the body-control motion, but relearning was rapid. They all had the usual difficulties learning to control timing of opening and closing. Also, all but one of the children reverted temporarily to the practice of pulling out objects to release them from the hook rather than actively opening the hook to drop them, and this situation occurred even after they had relearned the body-control motion for hook opening. These children showed one deviation from the learning pattern usually observed: they stopped pulling out objects and learned a reliable active-release pattern earlier than is usually expected from children who first receive a cable at two years of age.


Interpretation of these results by CAPP therapists offered some insight into the future uses of this fitting-training procedure, as compared to the method previously used. First, if early activation is elected, the learning sequence proposed by Trefler appears to be very appropriate for children at the age of 15 months. Since it is difficult for the child at that age to control hook closing, teaching the child to open the hook to drop an object is a more reasonable expectation as a first step at 15 months. Also, 15-month-old children still enjoy the simple repetitive play of moving objects into and out of containers.

In this CAPP study, it appeared that whatever was learned during the 15-16 month age period was all that was likely to be learned before the age of two years. Therefore, if the cable is introduced at 15 months, it is important to begin training immediately, since the child's interest in learning hook operation will last for only a very brief period before the onset of negative behavior, resistance to being handled, and the shift in interest to gross play activity.

Since developmental changes occur so rapidly at this age, CAPP therapists felt that a reliable developmental behavior indicator, rather than the chronological age of 15 months, should be used as a signal to add the cable. Perhaps the period after the child has learned to stand but before he can run well would be a time to introduce cable control and exploit his interest in manipulating objects.

Staff and parents should maintain realistic expectations when using the early-activation method. At CAPP this study indicated that early activation offers an alternate means of achieving the same result that has been achieved by previous methods. All children appeared to have retained some association between the body-control motion and hook operation; yet at the age of two years, when interest in hook use reawakened, they needed to learn almost as much as children who do not have a cable prior to that time. Early activation probably hastened relearning at age two, since the children in this study relearned cable control quickly. Also, these children developed earlier spontaneous patterns of active release.

Mechanical requirements for participation in the early-activation procedure are minimal. They relate primarily to the cost of the cable and the requirement that the harness and rubber-band loading be kept in optimum adjustment for skillful performance. Teaching parents to recognize the subtle differences in the child's performance by making these adjustments was an important benefit to those patients who participated in the study.

Problems with Early Activation

In general this study did not demonstrate a significant benefit to patients over the traditional methods, and CAPP has not adopted this procedure except for selected patients.

One therapist noted that instructing the child in cable operation at the age of two years was more difficult if the child has had a cable since the age of 15 months. This phenomenon occurred because a cable provided at two years of age offers a great deal of excitement for the child, and he has strong motivation to learn hook operation. If he has been encouraged to learn hook operation for the past nine months, his motivation to learn operation at age two is less intense, and training is more difficult. This finding was verified by other therapists at CAPP.

Another negative result was that the early-activation method may encourage inappropriate training attempts during negative periods. Although children are easy to work with for one-minute or two-minute periods at the age of 15 months, they soon become quite resistant to training, and it is the parent who is then in the position of trying to teach the child hook operation during a negative period. One key role of the therapist was to reassure parents that the child was going through a normal stage and that the parent should not force the child to learn hook operation while he is so negative.

Some parents in this study found the teaching of the body-control motion to be a considerable challenge. Not only did the child have to cooperate enough to allow the parent to place an object into the hook, but he also had to leave it there long enough for the parent to perform the body-control motion passively to drop the object. Therapists encouraged parents to have the child hold another object in the sound hand during this early learning period to keep the child from reaching over immediately to pull out the object before the parent could guide him passively.

CAPP therapists observed that parents who are not overly anxious about their child's achievements and are willing to devote some time to this type of training are good candidates for this procedure, while parents who do not like to handle the prosthesis or who need constant reassurance that their child is succeeding and doing well are poor choices for this approach.


From this investigation, there appears to be no significant advantage to early activation of the terminal device over later activation, except in selected cases. The study identified some criteria to guide the staff in selecting patients to follow the early-activation procedure.

Patient Benefit


Those children who can learn some of the hook-operating skill do so in a gradual manner at home rather than in a clinic training atmosphere.

Although children do not gain complete control over the cable, there may be some carry-over to later learning in associating the body-control motion with hook operation, and with earlier use of active release.

Even though the child does not learn cable control, he is not harmed by the experience.


It is unlikely that the child will learn to operate the hook well enough at 15 months of age to be able to utilize active grasp at that time.

Most children appeared to require almost as much training in hook operation at the age of two years as those who first receive a cable at that time.

Some parents overemphasize terminal-device use to the exclusion of gross patterns. Establishing spontaneous gross-use patterns is one of the major advantages of early fitting and should be encouraged.

There is considerable pressure on the child at an early age to perform a skill he cannot accomplish well due to his neuromuscular immaturity.

Parent Involvement


Parents learn to take responsibility for stimulating home use of the prosthesis, for making accurate observations, and for reporting skill and use patterns.

The procedure may be beneficial for those parents who feel the need to be actively involved in doing something for their child.

The schedule of appointments may be more suited to some families than the schedule required for training by a therapist at age two years.


Parents must be willing to take the responsibility for training their child. They may encounter strong negative behavior while training the child, and they may find this difficult to handle.

The procedure may be difficult for those parents who are overly concerned about their child's developmental status, or those who don't really have time to devote to this training but will not say so.

Mechanical Considerations


Parents learn how to observe the need for changes in fit and function of the prosthesis. Subtle changes in control-strap length and hook loading become meaningful, and parents become aware of their continuing responsibility to seek repairs as needed.


Some extra attention is required during the 15-to-24 month age period to maintain optimum adjustments for active hook operation over that required with passive fittings.


The author expresses appreciation to Susan Clarke, Carole Kral, and Joanne Patton, occupational therapists at CAPP, for suggestions and assistance.

Addendum: Information for Parents

  1. Show parents body-control motions for opening and closing the hook. Teach parents how to do motions passively. Show them the path of the cable and why the motion causes hook opening.
  2. Teach the parents how to remove and replace the cable in case of breakage. Show the parents the features of the figure-of-eight harness, and how to recognize signs of out-growth and need for adjustment. Show how to remove and apply the prosthesis with the figure-of-eight harness and how to interchange harnesses for laundering. Point out need to keep tight sleeves away from cable.
  3. Teach parents how to balance wrist-friction adjustment against rubber-band loading. Teach parents how to get the right amount of rubber-band load.
  4. Review sequence expected for learning to operate the hook. Stress only the phase that the parents will be expected to teach at that time: Release of objects from hook, relaxation of cable tension after an object is placed into the hook, reaching for an object to be placed into the hook, placing the object into the hook himself and, finally, operating bimanually with sound hand and hook at midline.
  5. Demonstrate games which can be used to teach the skill the child needs to learn next. For example, release of objects from hook can be done by dropping buttons or poker chips into a bucket.
  6. Be sure that parents understand that they are to encourage but not force the child to learn the skill through games, and that the times for teaching will probably be brief and as the child shows interest.
  7. The parents should be encouraged to start teaching the child the skill during the therapy session so the therapist can see that they understand the procedure and the approach to teaching.
  8. Ask the mother to observe the child's response to teaching sessions and to report any problems, progress, and spontaneous use by the child.

Editor's Note: Because Ms. Shaperman felt that her observations differed from those previously reported by Trefler, she submitted her manuscript to Ms. Trefler for review and comment. Ms. Trefier provided the following discussion. She is presently located at the Crippled Children's Hospital School. University of Tennessee, Memphis, Tennessee.


The opportunity to comment on Julie Shaperman's article entitled "Early Learning of Hook Operation" is appreciated. In actuality both Ms. Shaperman and Ms. Trefler reported similar findings. For a select number of patients with realistic parents, activation of the terminal device at approximately 15 months of age seems appropriate. If the child is very hyperactive or the parents prone to becoming overly concerned, then activation after two years of age is more appropriate. However, the advantages of parents'working with their young child in learning to operate a terminal device should not be overlooked.

Two methods of terminal-device activation have been presented. Each clinic must carefully evaluate each young amputee in regard to when the terminal device is best activated 15 months of age or after two years of age.

-Elaine Trefler

Child Amputee Prosthetics Project, University of California, Los Angeles, California. This work was supported by Grant No. MC-R-06004-08, Maternal and Child Health Service, Department of Health, Education, and Welfare.

1. Shaperman, Julie W., The Child Amputee: Observations on the Sequence of Learning Active Terminal Device Control, Masters Thesis, University of Southern California, 1960.

2. Trefler, Elaine, Terminal device activation for infant amputees. lnter-Clin. Inform. Bull., 9:9:ll, June 1970.

3. Wendt, Jeannine, and Julie W. Shaperman, The infant with a cable-controlled hook, a study of the development of prehension patterns. Am. J. Occup. Ther., 24:6:393-402, September 1970.