A Two-Piece Wrist Disarticulation Prosthesis

William A. Tosberg, C.P.O. Liesl Friedmann, O.T.R.

Following World War II an extensive survey revealed that only a small percentage of upper-extremity amputees derived worthwhile function from the prostheses provided them. Since that time, intensive research and education efforts have been directed toward the improvement of artificial arms, and those efforts still continue. This article describes an attempt to provide an improved prosthesis for one type of upper-extremity amputee.

Usually, the amount of function which can be obtained from an artificial arm increases in direct relation to the length of the stump. A shoulder disarticulation amputation offers the least possibility of prosthetic functional regain; a wrist disarticulation amputation offers the most. Yet it is questionable whether even in the wrist disarticulation prosthesis we have yet achieved the best possible results.

Since pronation and supination are still available in a wrist disarticulation amputation stump, it is essential that the prosthesis for this amputation level take advantage of and incorporate the maximum amount possible of this very important residual motion.

The standard wrist disarticulation socket is fitted closely to the styloids, reaches posteriorly almost to the olecranon, and is trimmed low over the anterior stump. This socket is connected to a triceps pad by means of flexible hinges. If such a prosthesis allows about 50 percent of the residual forearm rotation available in the stump, it is generally considered acceptable.

Typically, a below-elbow stump has a tapered configuration. Hence, the conventional socket can only be retained in its proper relationship to the stump by means of the harness, which therefore has to be tighter than if it were used for control of the terminal device alone. To eliminate the discomfort caused by this tightness, the so-called Muenster-type socket was

created. In this prosthesis the socket is fitted very snugly and is essentially suspended on the olecranon and humeral condyles. Hence, a simplified harness used primarily for control is all that is necessary. This type of socket, however, does not lend itself to long below-elbow or wrist disarticulation stumps. It would not only be very difficult to apply the Muenster socket to long stumps, but also no utilization of any remaining pronation or supination would be possible.

To overcome this dilemma, the prosthetic service at the Institute for Rehabilitation Medicine has constructed two-part sockets for several wrist disarticulation patients. The distal portion of this prosthesis is closely molded to the styloid processes, while the other part consists essentially of the proximal section of a Muenster socket, which is short enough to allow full elbow flexion. The two parts are connected by means of dacron webbing.

This configuration has been well received by our patients, especially by bilateral child amputees, who take full advantage of the active pronation and supination obtainable with these arms (Fig. 1 , Fig. 2 , Fig. 3 , Fig. 4 and Fig. 5 ). In addition to the retention of almost all residual pronation and supination available, an additional advantage is that adjustment for growth (which in young children is more linear than circumferential) is facilitated. By replacing the dacron connection, we can lengthen these arms rapidly and inexpensively.

It is recognized that pronation and supination will effectively change the distance between the olecranon and the end of the stump. This differential, however, has not yet created any problems, since the amount is minimal and the fit of the proximal section of the socket is not so critical as would be the case in a Muenster prosthesis for a short below-elbow stump.

William A. Tosberg, C.P.O. is the Technical Director, Prosthetics Service and Liesl Friedmann, O.T.R. is the Therapist-in-Charge of Children's Division Institute of Rehabilitation Medicine New York University Medical Center New York-, New York