The Development of Modular Joint Units for use with Actuators


A 16-year-old boy with a unilateral, right, upper-extremity amputation was fitted with a hydraulic arm prosthesis in February 1969. He had lost his arm at shoulder level as a result of electrical burns. Since the fitting the boy has returned to the Institute twice for follow-up examinations and for determination of the efficiency of this apparatus.

It was found that the hydraulic system functioned satisfactorily with this patient as was evidenced by utilization of the device in his activities in daily living. It was noted that the patient wore the apparatus daily.

In 18 months of use no leaks from the hydraulic system were reported. The batteries were recharged every night indicating that the energy storage was sufficient for the activities of each day.

The only problems encountered to date have been a broken wire on two occasions and poor contact in a switch in the shoulder vest at the acromion level, possibly as the result of perspiration.

A second hydraulic arm prosthesis is now available for fitting. It incorporates a hydraulically operated shoulder joint which permits active flexion and extension. Abduction and adduction will be performed passively. The elbow will also provide active hydraulically operated flexion and extension. The wrist will be a wedged unit which permits a certain amount of circumduction. It is hoped that a new hook design by the Northern Electric Company ( Fig. 1 ) can be incorporated into this arm.

Modular Hydraulic Elbow

A modular hydraulic elbow was developed for above-elbow amputees who require greater than usual elbow strength because of their occupations ( Fig. 2-A and Fig. 2-B ).

It is hoped to fit this elbow to a suitable candidate in the near future. One of the prime features of this device is that, depending on the level of amputation, the piston will be inserted in either the arm or the forearm; i.e., if the stump is short the piston will be inserted in the arm shell, thus ameliorating the weight problem.

Modular Wrist Joint

Three patients have tried a new type of wrist joint developed with the cooperation of Northern Electric Company ( Figs, 3-A and 3-B ). This wedged unit permits circumduction and locks automatically in any desired position. With the unit the terminal device can also be tilted in radial deviation to a maximum of 45 degrees.


In studying the use of external sources of power, e.g., pneumatic and electrical, it has been determined that, for the time being at least, three main types of switches are essential. These types are: a) push-button, b) pull, and c) rocking.

Rehabilitation Institute of Montreal Montreal, Quebec, Canada