Experience With The Muenster-Type Below-Elbow Prosthesis: A Preliminary Report

Charles H. Epps, Jr., M.D. John H. Hile


Following publication of a manual of instruction by New York University in 1965(1), our clinic undertook the routine fitting of short below-elbow cases with Muenster-type prostheses. The traditional problems which arise when very short and short below-elbow stumps are fitted with split-sockets and step-up hinges are well known. However, individual clinic experience in fitting Muenster-type prostheses to these patients has not been well documented. This paper presents an analysis of patients fitted with the Muenster-type prosthesis at the Juvenile Amputee Clinic of the District of Columbia General Hospital. The principles of construction and fitting outlined in the New York University manual were followed very closely.

Clinical Material

Fourteen patients were fitted with a total of 24 Muenster-type below-elbow prostheses between 1965 and 1967. Eight female and six male patients comprised the group. The right upper extremity was involved in eight patients, the left in six. There were no bilateral cases. One ten-year-old boy had an amputation of traumatic etiology; the remaining 13 patients had congenital deficiencies. An 11-month-old infant is not included in the analysis because her family moved to another city shortly after fitting, and no long-term follow-up data could be obtained. The length of stump varied from 1 1/4 to 7 inches, with all but two measuring less than 4 inches. The distribution is presented in the following table:

Table 1

During the study period two patients received three prostheses, six received two prostheses, and six had single fittings. In the multiple fittings, the shortest period before replacement was five months, the longest 26 months. The average for the entire 13 patients on whom adequate follow-up information was obtained was 11.8 months. One patient lost his prosthesis after ten months while water skiing. The three patients requiring replacement at five to six months gained weight rapidly or experienced growth spurts.

Fabrication and Fitting Procedures

Taking the wrap cast is one of the most critical considerations in preparing the Muenster-type prosthesis. Use of a proper molding grip is essential to the success of the technique. It was our experience that the stump of the young infant is more difficult to cast than that of older children because of the discrepancy between the size of the infant's stump and the hands of the prosthetist. Accentuation of the groove for the ulna formed by the thenar and hypothenar eminences seems to be less critical in casting the infant than it is in the older child or adult. This difference is probably due to the generous layer of subcutaneous fat so characteristic of this age. We have not made special efforts to relieve the olecranon during casting but do add a build-up to the male mold. Pressure at the posterior distal surface of the humerus above the epicondyle level and the two-fingered pressure on either side of the biceps tendon on the anterior surface of the stump are important factors (Fig. 1 ). On small patients, the middle finger is slightly bent because of the different lengths of the index and the middle fingers. A symmetrical socket brim which provides overall fit is the goal (Fig. 2 ). Aside from these minor differences, the casting and all the construction procedures, including lamination and harnessing, followed the NYU manual exactly.

The simplified harness system commonly referred to as the figure-nine harness, with the cable reaction point located on the proximal-posterior socket, was used in our series. For the nine-month-old patient a small triceps pad with conventional figure-eight harness was used, in order to make the prosthesis more secure. We felt that a nine-month-old patient with a 1 1/2 inch stump would be able to remove the prosthesis without the additional suspension provided by the triceps pad and the anterior forked strap (Fig. 3 and 4 ).

Evaluation

The value of the prosthesis was judged on two bases. First, the reactions of the patient and his parents were considered. Second, patient response and performance were compared with the checkout criteria published in the manual.

All patients and parents were pleased with the Muenster-type prosthesis. The simplified harness and light weight were consistently mentioned as favorable features. It was interesting to note that the seven patients who had previously worn other types definitely preferred the Muenster type. The patient who had worn the split socket was even more emphatic in his approval, as were his parents.

Standard checkout forms were used in the clinic. However, for purposes of this study, special attention was given to several specific items: range of motion with and without prosthesis, stability, and control system efficiency. These data are summarized in Table 2 .

Terminal device openings were recorded for all patients within the limits of 30 and 90 degrees of elbow flexion and were considered acceptable. The number of rubber bands varied between one-half a band to three, depending upon the functional requirements of the patients.

The recorded ranges of elbow motion without the prosthesis illustrate the hyperextension so characteristic of upper-extremity terminal transverse partial hemimelia. In our series maximum flexion varied from 80 to 100 degrees with the prosthesis for most patients. In all instances, full terminal device opening was obtained at maximum forearm flexion. The test of full terminal device opening at the mouth did not apply, as the terminal device could not be brought to the mouth. However, as all patients were unilateral, the flexion ranges were considered acceptable.

Retention of the prosthesis under axial load testing revealed suspension stability to be excellent, as most prostheses tolerated one-third of the child's weight without excursion of the socket. The greatest slippage recorded was one-half inch.

Control system efficiency was better than 80 percent in one-half of the prostheses, and in no instance was the percentage less than the 71 percent recorded in one case.

Perspiration has not been a problem even during humid summer days. All patients used cotton stockinette stump socks for insertion of the stump, with the ends tucked back into the forearm shell after donning. We believe that the opening provided in the medial socket wall for this purpose may have been a significant factor in heat regulation.

Summary

We have presented an analysis of our experience in fitting a total of 23 Muenster-type prostheses to 13 patients. The prostheses were fitted, with very minor modifications in casting technique, according to the New York University fabrication manual. Actually, the differences were more quantitative than qualitative. It should be mentioned that our clinic prosthetist attended the pilot course in Muenster-type fabrication technique at New York University. This technique may be better acquired by firsthand instruction than by independent reading of a manual.

The results have been very gratifying. The parents and patients found this prosthesis acceptable, and in seven cases preferred it to other types that had been previously worn. Although the range of motion in the prosthesis did not always equal the expected 70 degrees of active flexion, function was acceptable. The stability achieved was excellent. In no case was there more than 1/2-inch displacement of socket on the stump with one-third of body weight in axial pull. Control system efficiency was within acceptable limits in all cases, with one-half checking out at 80 percent or better.

On the basis of our limited experience, we believe that the Muenster-type prosthesis is the fitting of choice for the child with a unilateral short or very short below-elbow amputation.

Charles H. Epps, Jr., M.D. and John H. Hile are associated with the Juvenile Amputee Clinic D. C. General Hospital Washington, D.C.

References:
1. The "Muenster-Type" Below-Elbow Prosthesis ," Prosthetic and Orthotic Sudies, New York University, New York, April 1965.