Redesigned Wrist Flexion Unit Evaluated

An evaluation of a redesigned Child's Wrist Flexion Unit was recently conducted by New York University-Child Prosthetic Studies. The unit was originally designed by the Army Prosthetics Research Laboratory to meet the need for flexion at the prosthetic wrist. Developmental evaluation in 1959 led to a number of changes in the original design and the Hosmer Company began manufacture of wrist flexion units for commercial distribution.

Subsequent experience with the production units indicated three problems: (1) wear occurred in the aluminum web or bridge between the two rocker grooves, leading to inadvertent flexion and extension of the terminal device; (2) the outer edges of the two rocking grooves became worn and did not confine the plunger in the appropriate grooves, permitting the terminal device to move to 90 degrees of flexion and to hyperextension; and (3) small separate nylon plugs were originally provided for the terminal device set screw well. These discs were frequently lost and resulted in damage to the terminal device stud threads from the unplugged set screw. It became extremely difficult to remove the terminal device when this occurred.

In an effort to eliminate these problems, APRL further modified the unit and its present characteristics are: (1) 35 degrees of flexion; (2) pressed fit fiber plugs inserted at the base of the set screw well to prevent damage to the stud threads of the terminal device; (3) steel pin inserts in the aluminum web between the two rocker grooves; and at the top of the external walls of the grooves; (4) the two rocker grooves have been machined .010" deeper.

Study of Redesigned Device

NYU sought to evaluate the redesigned device in the following areas: (1) cosmetic acceptability of the unit by patients and parents; (2) weight considerations; (3) function - ease and method of operation and usefulness in practical activities; (4) durability; and (5) maintenance.

Since the earlier evaluations had indicated that the unit's greatest potential usefulness was in the fitting of patients with high bilateral amputations, two girls, aged 12 and 4 (bilateral above-elbow) and one boy, aged 9 (bilateral shoulder-disarticula-tion) were selected to participate in the study.

During the initial four weeks of the study, each child wore a functional wrist flexion unit on the non-dominant side and a non-functional unit on the dominant side. During the second four-week period, the unit on the dominant side was adjusted for function while the unit on the non-dominant side was made inoperable. During the final four weeks, the child wore functional units on both prostheses.

Subject DW, a bilateral above-elbow amputee, now 13 years old, had worn earlier models of the unit for several years. She had worn the current model for five months through October, 1962. She is also a unilateral hip-disarticulation amputee, and is predominantly "left handed" with her right upper extremity playing a subsidiary functional role. Partly for these reasons, she elected to retain the unit on the left (dominant) side only, preferring to have a non-flexing wrist on the right side for leaning on the floor, table or desk, and for support in case of a fall.

Among the activities which she accomplished without the unit but were more easily or efficiently performed with it were: brushing and combing hair, buttoning and unbuttoning clothing, adjusting pelvic belt, and holding books or similar objects against the body. Activities possible with the unit but not possible without it related primarily to toilet - the manipulation of clothing and after care.

Subject KC, a bilateral above-elbow amputee, was fitted with the units at the age of 4 1/2. She also has bilateral above-knee amputations and spends much of her time in a wheel chair, although she does ambulate two hours per day with crutches attached to the wrist units of the arm prostheses. Through October 1962, she had worn the units for four months. Activities more easily performed with the units were: bringing a cup to her mouth, eating cookies and similar food, cuddling dolls and stuffed animals, and manipulation of toys. KC elected to keep both units. Her mother commented, "She is learning to do new things with them all the time."

Subject JS, a 9-year-old boy, is a bilateral shoulder-disarticulation amputee, and also wears a non-standard prosthesis on his right leg. He had worn the units for five months through October 1962. JS was able to untie his shoe laces and operate fly zippers with the units, which he was unable to do before their installation. He found it easier to eat and write with the units than without them. JS also decided to retain both units. As with KC, the choice was based as much on possible future potential as the present need for two units.

Pushing against the thigh to flex or extend the wrist was the procedure most commonly used by the children. However, pushing against tables, desks and other objects, was frequently employed. Initially, KC (the youngest subject) used her opposite terminal device and JS used his chin.

Each child experienced inadvertent operation in the course of the study. In the case of the two older children, the malfunction was corrected by increasing the spring tension on the flexion unit plunger. KC's problem disappeared as she acquired more skill in the manipulation of the devices. Loss of the lateral screw on one unit was the only other item requiring maintenance. Within the relatively brief period of the study, there was apparently no significant change in plunger tension with use.

Fig. 1 , Fig. 2

Conclusions and Recommendations

The study of the redesigned unit tended to confirm the findings of the earlier studies as follows: (1) no significant negative features associated with the wear and use of wrist flexion units were identified. Cosmesis was acceptable and the weight of the units was not an appreciable factor. Major problems were not encountered either in the operation of the units per se or in the prostheses as a result of the addition of the units; (2) all three children demonstrated a significant improvement in the performance of certain functions, and some activities which could not be performed previously were now possible.

In regard to the question as to whether the flexion units should be fitted unilaterally or bilaterally, the study indicated that bilateral fitting is desirable. It would be useful, as a "fudge" factor, to have a spacer and fairing which could be used in place of a flexion unit if it were found unnecessary.

The problem of inadvertent operation which prompted the study appears to have been markedly reduced, and perhaps could be made virtually nonexistent with proper installation and adjustment of the flexion units (maximum tension commensurate with facile operation). On the basis of their findings, NYU recommended that information concerning the modifications incorporated in the test units be made a-vailable to the manufacturers) who are interested in providing the units commercially.