The "Muenster-Type" Below-Elbow Prosthesis: A Field Study

Ann Gorton, R.P.T.


During the past year New York University has been conducting a field study to determine the applicability of the "Muenster-Type" below-elbow prosthesis to juvenile amputees. Fifty-four children treated at 16 child amputee research program clinics have participated in the study. Their prostheses were fabricated by prosthetists who attended a one-week course in the technique at New York University in April 1965, and in accordance with the procedures described in A Fabrication Manual for the "Muenster-Type" Below-Elbow Prosthesis.

The general characteristics of the experimental limb are (1) the socket is set in approximately 35 degrees of initial flexion; (2) the anterior trim line extends to the antecubital fold (with a channel provided for the biceps tendon), and the socket also encompasses the epicondyles and olecranon; (3) the range of motion is limited to approximately 70 degrees; and (4) a simplified harness system (Proximal Reaction Point System) is employed (Fig. 1 Fig. 2 Fig. 3 and 4 ).

A final detailed report on the findings of the field study is being prepared for publication. This report will indicate that the "Muenster-Type" prosthesis offers definite advantages to the child with a short below-elbow amputation. However, a few problem areas have been reported and the present article will consider these problems and the procedures that may be used to alleviate them. Reports from readers are solicited concerning modifications made in their own clinics to enhance the overall effectiveness of this prosthesis.

High Acceptance Level

Evaluation of the data received thus far indicates a high degree of functional and cosmetic acceptance by children, parents, and clinic personnel. Forty-two children (13 males, 29 females) completed the three-month test-wear period planned for the study by July of this year. The majority of these patients rated the "Muenster-Type" prosthesis as being "very satisfactory" or "satisfactory" in the following respects: socket and harness comfort, weight, general appearance, effort to operate, and socket retention.

Of the 42 children, 33 (79%) considered that the experimental prosthesis offered distinct advantages over their prior-worn limbs and elected to continue its use rather than revert to the type of limb previously worn. Nine children (representing six clinics) rejected the limb after three months of wear. In eight instances the rejection was attributed to a reduction in range of elbow motion. One prosthesis was rejected because the child lived 250 miles from the clinic, making visits for socket adjustments impractical.

Despite the high level of acceptance accorded the "Muenster-Type" prosthesis, its negative features have been mentioned with sufficient frequency as to warrant discussion. The problems, in order of the frequency with which they were cited in clinic reports, are reduced range of elbow motion, clothing wear and harness discomfort caused by the low-riding cable, and problems related to growth.

Limited Range of Motion

Twenty-five of 42 children (7 males, 18 females) were apparently not handicapped functionally by the decreased range of motion. All of these children were fitted unilaterally except for one 11-year-old girl with bilateral 2-5/8" below-elbow stumps (acquired amputations). Even in this bilateral fitting, the limited range of motion did not appear to affect the child adversely. However, the clinic is deferring final evaluation until the child has become more accustomed to the experimental limbs. After three months of wear, the child indicated a preference for the conventional prostheses, feeling that they "perform more easily." The foster parent preferred the "Muenster" prostheses, since the child was "unable to take her stumps out of the sockets as she used to with her old prostheses."

Seventeen children (6 males, 11 females) fitted unilaterally found that certain bimanual activities were less easily performed or were prohibited by the limited range of motion. Nine of these 17 children (1 male, 8 females) were willing to tolerate this limitation in order to secure the benefits of the improved cosmesis, better socket retention, and greater harness comfort provided by the "Muenster" prosthesis. Eight children (5 males, 3 females) rejected the "Muenster" prosthesis in favor of the prior-worn limb (four double-wall sockets, three with flexible hinges and one with a polycentric hinge; three split sockets, two with step-up hinges and one with a stump-activated elbow hinge; and one preflexed socket with a flexible hinge) primarily because they could not perform bimanual activities that required extreme elbow flexion and/or extension.

Reduced elbow flexion imposed the major restriction. Specific activities cited as requiring more flexion than was provided in the "Muenster-Type" fitting were hair grooming, buttoning a shirt, gymnasium activities, and activities performed at table level such as cutting meat, working with tools, and typing. Two children commented that limited extension hindered performance in golf and washing dishes

Relation to Age and Sex

It would appear that limb rejection due to limited range of motion is related in some degree to the sex and age of the child (Table 1 ). All the boys eight years and older desired more elbow flexion in order to perform accustomed bimanual activities. This factor was seemingly less important to most of the girls; improved cosmesis and comfort apparently outweighed the limitations imposed by decreased flexion range. Dr. Pellicore, in a report on nine children fitted in Chicago with the Hepp-Kuhn prosthesis, also found that girls tolerated the limited motion better than boys.2 However, three older girls (ages 10 to 19) felt that the "Muenster" prosthesis significantly restricted activity and preferred their prior limbs, which permitted more elbow motion.

Socket Fit

Accurate socket fit is essential for maximum prosthetic function. If the elbow flexion range is appreciably less than 70 degrees, the possibility of prosthesis rejection increases. Although the suggested range of motion is not always possible (especially on short stumps), a close approximation is most desirable.3 Should the range of motion provided fall significantly short of this goal, the limb should be carefully checked to determine whether optimum socket fit has been achieved-i.e. one which will allow maximum motion without sacrificing retention. Factors which limit range of motion are insufficient relief for the olecranon and/or biceps tendon and high trim lines.

In one instance a child was fitted with two "Muenster" limbs. The first was rejected primarily because limited elbow motion (30 to 80 degrees flexion) did not allow the child to perform activities above the chest level. A second prosthesis, which provided 15 degrees additional motion (60 to 125 degrees flexion), was then fabricated. The child was satisfied with the second fitting, stating that she had sufficient elbow flexion to meet her needs.

Additional Socket Preflexion

Several clinics have reported successful fittings in which the socket was set in 5 to 20 degrees more initial flexion than the suggested 35 degrees- that is, the inner sockets were preflexed up to 55 degrees. In these instances motion was taken away from an area seldom utilized prosthetically (extension) and added to the more functional end of the range of elbow motion (flexion). It is conceivable that a child wearing a socket with 55 degrees of initial flexion might object to the cosmesis of the limb. However, seven children who wore prostheses in which elbow extension was restricted by 50 to 55 degrees (relationship of the prosthetic forearm shell to the humerus rated cosmesis as either "very satisfactory" (two children) or "satisfactory" (five children).

Cable Interference With Clothing

The configuration of the "Muenster" socket provides excellent retention, thus eliminating the necessity of a triceps pad and a front support strap. Many clinics have noted that the Proximal Reaction Point System Harness which may be used provides greater comfort and more freedom of movement (Fig. 5 and 6 ). However, in some instances it was found that the control attachment strap, riding low across the back, pulled against tightly fitting sleeves and caused discomfort and clothing wean This problem may be eliminated by application of a Triceps Reaction Point System, consisting of an axilla loop and a housing crossbar assembly mounted on a small triceps pad, which is secured to the upper arm by a Velcro strap (Fig. 7 ). This system raises the cable enough to prevent drag in the sleeve but does not add a front strap. Hence the simplicity of the harness is still maintained to a certain degree. When test-worn in the New York University laboratory, this harness system proved to be quite satisfactory, with no rotation of the triceps pad on the upper arm evident. Should this method prove to be unsatisfactory, the standard figure-eight harness with triceps pad or half-cuff may, of course, be applied.

Growth

It is conceivable that the total time a given prosthesis can be worn would be reduced by a snugly fitting "Muenster-Type" prosthesis. The field study has not yet been in progress for sufficient time to provide valid data on total length of prosthetic wear for the participants. However, in the prior laboratory study of juvenile fittings conducted at New York University, seven of 13 limbs fitted were worn for periods longer than one year. The shortest period of wear was one month (by a nine-year-old boy who underwent a growth spurt following surgery to the genitals).5

In an attempt to prolong the period of prosthetic wear, both New York University and Sunnyview Rehabilitation Center in Schenectady, N. Y., have fitted triple-wall laminated "Muenster" sockets to children with below-elbow amputations. Although the sample has been small, the results indicate that triple-wall lamination is a plausible method of extending the wear period.

Two children, each with unilateral below-elbow amputations, were fitted with triple-wall "Muenster-Type" prostheses in the New York University laboratory. A nine-year-old boy wore his limb seven months before the inner socket was removed to accommodate stump growth. The child subsequently wore the limb for 15 months. A two-year-old girl wore her triple-wall "Muenster" prosthesis for six months before the inner socket was removed, and then continued wear for five additional months.

The method of socket fabrication, whereby the inner socket is easily removed to accommodate an increase in stump girth, is identical to that described by Dr. William E. Gazeley et al. in the December 1964 issue of the ICIB6.

Summary

As with other prosthetic fittings, the "Muenster-Type" prosthesis has inherent advantages and disadvantages which should be carefully weighed at the time of prescription. The child's age, sex, stump length, and prosthetic utilization should be evaluated in relation to the negative as well as the positive attributes of this fitting technique. The maximum motion obtained with the "Muenster" prosthesis will be significantly less than that provided by the conventional preflexed or split socket limb. If the child actively utilizes his appliance in bimanual activities requiring full elbow flexion and/or extension, the "Muenster" prosthesis is less desirable than one permitting greater elbow motion. However, when a limited range of elbow motion is acceptable (as it has been for 79% of the field study sample to date), the "Muenster-Type" prosthesis has much to commend it. The limb should be carefully examined to be sure that optimum socket fit has been achieved -i.e. one which will provide socket retention and comfort while allowing maximum elbow motion.

Methods for overcoming cable interference in clothing and for lengthening prosthetic wear have been discussed. A Triceps Reaction Point System is recommended for the former problem and a triple-wall socket for the latter. Further investigation of the triple-wall socket would be desirable in order to determine:

  1. Its effect on the wear-life of the prosthesis for a large sample of children.

  2. Whether stump growth is uniform, so that conformity of socket to stump is maintained when the inner socket is removed.

Ann Gorton, R.P.T. is associated with the Prosthetic and Orthotic Studies New York University Post-Graduate Medical School New York, New York

References:
1. A Fabrication Manual for the "Muenster-Type" Below-Elbow Prosthesis, Prosthetic and Orthotic Studies, Research Division, School of Engineering and Science, New York University, New York, 1965.
2. Pellicore, Raymond J., "Experiences With the Hepp-Kuhn Below-Elbow Prosthesis, A Preliminary Report," Inter-Clinic Information Bulletin, Vol. III, No. 11:1-7, September 1964.
3. A Fabrication Manual for the "Muenster-Type" Below-Elbow Prosthesis, op. cit., p. 18.
4. Ibid., p. 32.
5. Evaluation of the "Muenster Type" Below-Elbow Prosthesis. Interim Report, Child Prosthetic Studies, Research Division, School of Engineerin and Science, New York University, New York, 1965.
6. Gazeley, William E., M. C. Ey, and W. Sampson, "Use of Triple Wall Sockets for Juvenile Amputees," Inter-Clinic Information Bulletin, Vol. IV, No. 2:1-4, 8, December 1964.