Should the Münster Below-Elbow Prosthesis be Prescribed for Children?

Liesl Friedmann, O.T.R.


The Münster below-elbow socket was developed by Hepp and Kuhn in 19547 to provide a fitting for short- and very-short-below-elbow amputees ( ) which would maintain stability without the use of split sockets, rigid elbow hinges, or harness suspension6 ( ).

Suspension is attained entirely by shaping the tightly fitting socket to conform to the bony and muscular contours of the stump, and to grip the epicon-dyles and the biceps tendon7,11 ( ). The socket is sometimes fitted so tightly that no stump sock can be used, and in some applications a lubricant must be used on the stump for insertion8. Occasionally, stump socks, protruding through a hole in the socket wall ( ), are used to pull the stump into the socket. If a figure-eight harness is needed for suspension, then the socket has been fitted too loosely and is not functioning as a Münster prosthesis should, i.e., be curved above the olecranon process and the humeral condyles so as to grip them. Anteriorly, the trim line is at the antecubital fold, with freedom for the bicipital tendon, yet the socket grips both the anteroposterior and mediolat-eral aspects of the stump. Kuhn7 has stated that usually the Münster socket needs only a figure-nine harness for activation10, thus implying that on occasion the figure-eight is needed. He does not specify whether this requirement is for adults or for children. VanDerwerker and Paul11 have described a "modification" of the Münster socket which provides increased clamping over the epicondyles and eliminates pressure around the biceps tendon, with a lower trim line and improved elbow flexion.

To facilitate reaching the mouth with the terminal device, and to maintain the stump in the socket, the use of a "banana-shaped" forearm9 with a conventional socket, or the preflexed socket ( ) has been recommended. In the "banana" fitting the bore of the proximal portion of the socket is parallel to the long axis of the stump. The olecranon is not enclosed within the socket. The prosthetic forearm is curved from the distal end of the stump to the wrist unit ( ). A figure-eight harness with flexible elbow hinges is used with this socket. The patient's elbow can be completely extended, and in flexion the hook can be brought closer to the mouth because of the curvature of the forearm. Elbow flexion is limited only by the level of the anterior trim line, which is usually low.

As generally used, the term "preflexed socket" connotes an acute angulation immediately distal to the socket entrance ( and ) and, when this socket is worn, the patient's elbow is somewhat flexed ( ). The socket fits loosely over the olecranon and the humeral condyles.

Various combinations of the described prostheses are used, with flexion at the elbow and a curved forearm shaft. No suspension is provided by the socket, all being supplied by the harness.

The advantages claimed for the Münster below-elbow socket over the split socket are: increased power of elbow flexion, elimination of rigid elbow hinges, and improved cosmesis. The advantage over the preflexed and "banana-shaped" sockets with figure-eight harness is only improved cosmesis due to a decrease in harnessing if a figure-nine rather than a figure-eight harness is used. Cosmetic disadvantages of the Münster socket arc the partial elbow flexion ( ), secondary foreshortening of extremity length, and an olecranon bulge ( ).

In children, we have found that a figure-eight harness is usually needed. When this is used there is no advantage to a tight socket design and many disadvantages. For this reason, we do not believe that the Münster socket is advantageous for children when socket suspension is required. When suspension

Straps are not used, epicondyle clamping such as described by VanDerwerker and Paul should be employed.

Review of Fittings

All the patients seen by the Children's Service of the Institute of Rehabilitation Medicine, New York University Medical Center-from 1964 when the first Münster sockets were used to January 1, 1971-who had short or very-short-below-elbow stumps, were included in this study. One patient with bilateral amputations, three fitted with stump-activated elbow locks, and three others who had not yet received their first prosthesis were excluded from the study (Tables 1 and 2). Follow-up data are reported only on children who had worn preflexed prostheses prior to fitting with Münster arms (Table 3).

Data from our clinic indicate that of 65 Münster sockets fitted only 38 had adequate suspension from the socket to enable us to utilize a figure-nine harness. Of these, eight prostheses eventually had to be converted to figure-eight harnesses because of loss of suspension and/or socket rotation. With four other prostheses, use of the figure-nine harness was continued despite external rotation of the socket on the forearm. Acceptance of limitations in motion and rotation was especially noted with girls who were primarily interested in cosmesis.

The standard for successful wear of a Münster prosthesis at the Institute of Rehabilitation Medicine is that the patient wear it for at least one year with the figure-nine harness. By this standard, success with the Münster socket design was attained in 11 of 65 patients who required 15 prostheses. The average patient-age at which success was attained with the Münster prosthesis was 11 years. 8 months. The average age at which the Münster prostheses were delivered and subsequently failed was 9 years. 8 months.

The most important indicator of failure is average length of wear before socket modification or replacement is required. For the Münster socket, average length of use was 13.2 months and for the looser preflexed socket average length of use was 22.2 months (Table 4).

Discussion

As members of the staff of the New York University Prosthetics Research group, Fishman and Kay2 described the characteristics of the Münster socket but did not distinguish between fittings for adults and children. In a number of studies2,4,5,6 it was indicated by this group that the Münster-socket design made in the United States varied somewhat from the design in Münster. No epicondyle clamp action was claimed by these authors.

Gorton4 observed that 80 per cent of the children in her study considered the prosthesis to have advantages after a three-month test-wear period; however. 20 per cent of the children rejected the limb after three months of wear because of reduction in range of elbow flexion. This was the most significant negative finding of her study. Other disadvantages were excessive clothing wear, and harness discomfort caused by the low-riding control-attachment strap and cable. Males rejected the limb more often than females. Cosmetic improvement by elimination of the figure-eight harness was said to be the reason for improved acceptance by girls.

Gorton also followed the use of this prosthesis by 53 children5. She studied 19 males and 34 females and accepted three months' wear as "successful" fitting, whereas our standard at the Institute of Rehabilitation Medicine is wear for one year. As we found in our cases also, Gorton cited restricted range of motion as limiting the performance of activities such as hair grooming, garment fastening, tying neckties, table-level activities such as cutting meat, typing, and working with tools, and athletic activities. She pointed out that all boys over eight years of age wanted more elbow flexion. Other authors have found7,11 that excessive clothing wear can be eliminated by use of a triceps reaction-point system but this modification increases harnessing and decreases cosmesis. Epps and Hile1 fitted 14 children, and found an average length of wear before socket replacement of 11.8 months.

Gazeley et al.3 reported on four children fitted with the Münster below-elbow prosthesis, but no conclusions concerning the value of the technique were drawn by the authors.

One of the reasons for fitting a patient as early as possible is to encourage him to use the prosthesis naturally as an assistive extremity later in life. This early fitting prevents the patient from becoming dependent upon the use of the intact hand or other sensate body parts in substitution patterns. It is our impression that the Münster design, by inhibiting elbow flexion, is detrimental in that it tends to make patients reject the prosthesis for some or all activities and resort to the use of other body parts to accomplish their activities of daily living.

The socket described by VanDerwerker and Paul11, which uses only epicondyle clamping for supension, is apparently successful, and this design merits more extensive trial. These authors also recommend the use of the "butterfly harness" to diminish clothing wear.

Conclusions

Our experience with the Münster below-elbow socket has convinced us that this prosthesis is by no means the final answer for the majority of juvenile amputees with unilateral very-short or short-below-elbow reduction deformities. Most children with this type of stump must use a figure-eight harness since they cannot obtain adequate suspension from the Münster-type socket. The figure-nine harness is much less efficient because of poor-control-strap alignment.

We feel that the Münster below-elbow prosthesis should not be prescribed for children below the age of 11 years. After the age of 11 it should be prescribed rarely, and then primarily for girls interested in a functional-cosmetic prosthesis.

Acknowledgments

For the assistance given by Lawrence W. Friedmann, M.D., Chester Swin-yard, M.D., Ph.D., and Denyse Winters, C.O.T.A., in the preparation of this article, the author expresses her sincere thanks.

Clinical Supervisor Children's Occupational Therapy Institute of Rehabilitation Medicine New York, New York

References:
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Gorton, Ann, The "Muenster-type" below-elbow prosthesis, a field study. Inter-Clin. Information Bull., 6:1:12-18, Oct 1966.
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Tosberg, William A., Personal communication, 1971.
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