An Intersting Terminal Device Modification

Diane Ritter, O.T.R. Fred S amnions, O.T.R.

The successful fitting and training of a patient whose initial response to prosthesis is poor can sometimes be accomplished by special adjustments of prosthesis adapted to the habitual motions of the wearer. Such a case was encountered in the University of Illinois Amputee Clinic in March 1965.

The patient (K.G.) was a 2-l/2 year old girl with a left congenital below-elbow anomaly with syndactylous fingers.

The non-standard below-elbow prosthesis prescribed had the following features: (1) a socket cut-out to fit the anomaly, (2) a triceps strap closure rather than a figure-of-eight harness, and (3) a finger cuff for the syndactylous stump so that the terminal device could be operated directly by stump flexion (Fig. 1 ).

Following the initial checkout of the prosthesis, the child was referred to Occupational Therapy for use training (Fig. 2 and Fig. 3 ).

Training Difficulties

After twenty hours of individual therapy it was found that K.G. seemed unable to learn to use the prosthesis in a functional manner and displayed continued reluctance to its use, despite the fact that parental support and supervision were evident.

The possibility that this type of fitting might not be the most practicable for the patient was considered. It was observed that she lacked the power to operate the number of rubber bands required to obtain sufficient prehension for activities appropriate to her age. It was further noted that when the child worked with objects held in her hook, she tended to flex her syndactylous stump, thus inadvertently opening the terminal device and dropping the objects. These incidents produced frustration in the child and resulted in decreased voluntary use of the prosthesis.

A New Approach

After discussion with Dr. Claude N. Lambert, Clinic Chief of the University of Illinois Amputee Clinic, this prosthetic problem was taken up at a session of the Upper Extremity Course at Northwestern University. There, the recommendation was made by Fred Sammons, O.T.R. that an attempt be made to convert the patient's hook from voluntary opening to voluntary closing. Mr. Sammons also offered to undertake the job of revising the hook in this manner. Fig. 4 shows the hook before revision. Note that the hook had only one pound of pinch force.

Mr. Sammons converted a right hand hook to a left hand item by welding one end of a lever bar to the thumb portion of the hook. The finger cuff was fastened to the other end of the lever bar. Hook opening was maintained by a conventional rubber band, extending from the lever arm to the base of the hook (Fig. 5A/5B and (Fig. 5A/5B , (Fig. 6 ). With this arrangement the patient could obtain 3-1/2 pounds of pinch force.

Effects on Behavior

In the first training period after the modification of the hook (Fig. 7 and Fig. 8 ) a remarkable change in the patient's behavior was observed. She voluntarily operated the hook and used the prosthesis as an assistive device in every activity presented. She was now able to achieve adequate prehension at each initial attempt, and no longer suffered continual frustration. Her attention span appeared to be much longer and she tolerated the entire hour's training period with few protests. The child's increased initiative and her repeated successes in grasping and holding were also reflected in a more positive response on the part of the mother.

Advantages of Voluntary Closing

A voluntary closing terminal device simulates normal prehension more accurately than does a voluntary opening device and this similarity has a particular relevance in bilateral grasping activities. The normal hand functions on a voluntary closing pattern and when the terminal device requires voluntary opening, there is an opposition of patterns of movement in two-handed grasping. Performing different hand patterns simultaneously is difficult to learn, particularly for the pre-school child who is still developing refinement of prehension.


The success achieved with this child, plus previous experience with the problem of insufficient prehension in pre-school children, leads us to the belief that the voluntary closing terminal device deserves greater consideration in prosthetic fitting of the pre-school upper extremity amputee.

Diane Ritter, O.T.R. and Fred S amnions, O.T.R. are associated with the University of Illinois Amputee Clinic Chicago, Illinois