Field Study Of The Muenster-Type Below-Elbow Prosthesis

New York University Reports Published


In March 1967 four reports of interest were published by New York University Prosthetic and Orthotic Studies. Three of these reports are summarized in this issue of the Inter-Clinic Information Bulletin. Highlights of the fourth article-dealing with a survey of 1,018 limb-deficient children-will be printed in a subsequent issue. Copies of the complete reports may be obtained by writing to Dr. Sidney Fishman, New York University Prosthetic and Orthotic Studies, 317 East 34th Street, New York, New York 10016.

A preliminary report of this study was published in the October 1966 issue of the Inter-Clinic Information Bulletin (Vol. VI, No. 1).

Positive results obtained in evaluation studies of the Muenster-type below-elbow prosthesis conducted in New York University's laboratory led the Subcommittee on Child Prosthetics Problems of the Committee on Prosthetics Research and Development to recommend that a broad-scale evaluation of the prosthesis be initiated in the participating juvenile amputee clinics. The field study was to serve a twofold purpose: to familiarize clinic personnel throughout the country with this method of fitting children with below-elbow deficiencies, and to provide an opportunity to assess the applicability of the technique to a nationwide sample of children.

Data on 53 children (19 males and 34 females) were obtained from 16 juvenile amputee clinics. The ages of the children ranged from two to 19 years, and all but one had unilateral below-elbow deficiencies. One bilateral below-elbow amputee was included in the sample. Actual stump lengths ranged from one inch to 7 1/2 inches. The majority of the children (85%) had worn prostheses prior to their participation in the study.

The prostheses worn in the field study were fabricated by prosthetists who attended a one-week course in the technique at New York University, and in accordance with the procedures described in A Fabrication Manual for the "Muenster-Type" Below-Elbow Prosthesis (Prosthetic and Orthotic Studies, New York University, New York, 1965).

The general characteristics of the experimental limb (Fig. 1 and 2 ) 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), the socket also encompasses the epicondyles and olecranon; (3) the range of motion is typically limited to approximately 70 degrees; and (4) unless contraindicated, a simplified harness system (proximal reaction point system) is employed.

Of 51 children (two being lost to follow-up before sufficient data were obtained) 41 (80%) found the Muenster-type limb highly satisfactory, while 10 (20%) ultimately rejected the limb in favor of the prior-worn type of socket (four preflexed, three double-wall, and three split sockets). The high acceptance rate may be attributed primarily to the following positive factors:

Increased Stability (Socket Retention). The intimate encapsulation of the amputated stump and olecranon increased the lifting power available to the child. Positive findings in live-lift and axial load tests were corroborated by the large number of children who reported that lifting, carrying, and climbing activities were more easily performed with the Muenster-type prosthesis than with prior-worn limbs.

Socket Comfort. Because of the intimate socket fit, motion of the stump within the socket was minimal.

Harness Comfort. Elimination of the triceps pad and front support strap resulted in a feeling of freedom not experienced with the figure-eight harness.

Cosmesis. Improved cosmesis was related to the minimized harness system.

The negative features of the Muenster-type prosthesis most often cited were:

Decrease in Range of Motion. Limited elbow flexion proved to be of greatest concern to older children who were accustomed to wearing a prosthesis that permitted full range of motion and whose pattern of prosthetic utilization involved activities requiring extreme elbow flexion. This was the primary reason for rejection of the limb by the ten children who preferred prior-worn prostheses.

Harness Discomfort. The control attachment strap, riding low across the back, pulled against tightly fitting sleeves, causing discomfort and clothing wear. This problem can be relieved prosthetically by lengthening the control attachment strap, installing a triceps reaction point harness, or, as a last resort, using a standard figure-eight harness.

Some clinics expressed concern that the rapidly growing child might not be able to wear the intimately fitting "Muenster" socket as long as a more standard type. Follow-up data on 19 percent of the sample showed that the mean wear period before limbs were discarded because of growth was approximately ten months. Two-thirds of the sample continued to wear their limbs and have done so for an average of 15 months-the maximum wear period reported to date being 21 months. If desired, a triple-wall laminated socket can be used to prolong wear.

The great majority of the prosthetists participating in the study reported that both the time and the effort involved in the fabrication and maintenance of this limb were the same as or less than for other below-elbow prostheses. Since socket fit is critical, it is essential that prosthetists be adequately trained before undertaking this particular fabrication technique. Upon delivery, the prosthesis should be carefully examined to be sure that maximum elbow motion has been achieved without sacrifice of socket stability.

The Muenster-type prosthesis appears to be most useful for children with unilateral short or very short stumps; children with longer stumps and bilateral amputations probably gain less from this type of fitting. The socket modifications which are often required for donning and doffing the prosthesis when a long stump is fitted may result in decreased socket retention. Although loss of residual forearm rotation did not prove to be a problem in this study, it is a factor to be considered when fitting a child with a long stump. The applicability of this type of fitting to the bilateral amputee remains undetermined, since only one was included in this sample. However, limited elbow flexion did prove to be a problem for this child.

As with other prosthetic fittings, the Muenster-type prosthesis has inherent advantages and disadvantages. In this evaluation the positive features, such as increased socket stability, comfort, and cosmesis, outweighed the major disadvantage of decreased elbow motion for the majority of the children participating in the field study.

-Ann Gorton

Dorrance Model 2 Hand Field Study

A field study of the Dorrance No. 2 hand was initiated in February 1965 by New York University upon the request of the Subcommittee on Child Prosthetics Problems of the Committee on Prosthetics Research and Development. The purpose of the study was to determine the acceptability of the hand by a sampling of children and parents over a broad geographical area, to investigate its durability, and to identify functional strengths and weaknesses in bimanual activity performance.

The Model 2 hand was developed and manufactured by the D. W. Dorrance Company to meet the needs of children ranging from large seven- and eight-year-olds to small 11- and 12-year-olds. It consists of a metal hand shell and two moving fingers (index and middle) which articulate at the metacarpophalangeal joints; a thumb which moves with the two fingers and allows a maximum opening of 2-5/8 inches between thumb and index finger tips; and plastic foam "floating" fingers (ring and little) individually attached to the hand shell, which permit a small degree of passive movement (Fig. 3 ).

Hand function is of the voluntary-opening spring-closing type, i.e., a pull on the control cable opens the movable fingers and thumb against a spring force which closes them when cable tension is relaxed. The hand mechanism provides a pinch force of approximately 3 1/2 pounds and requires about 9 pounds of force to achieve complete finger opening (lighter-weight springs may be inserted to lower these forces). The hand weighs approximately 217 grams, and the overall dimensions are length, 5 1/2 inches (with fingers extended); width, 2 1/2 inches; thickness, 2 1/2 inches; and circumference, 6 3/4 inches.

Thirty-three children with unilateral upper-extremity deficiencies participated in the study, through the cooperation of 18 juvenile amputee clinics. Their ages ranged from six to 13 years, with 15 of the children being male and 18 female. Twenty-four had below-elbow deficiencies and nine were above-elbow amputees. All had been prosthesis wearers for at least six months prior to the study; 17 had worn a hook, nine a hand (six APRL-Sierra No. 1 hands, three Robin-Aids hands), and seven a hook and hand interchangeably.

The evaluation was based on child, parent, and clinic reactions to the experimental hand and to other previously worn terminal devices. Data on hand malfunctions were obtained from the prosthetists as well as from the manufacturer to whom the hands were sent for repair. During the six-month wear period covered by the study, data on each child were obtained on four occasions.

Subjectively the children generally indicated satisfaction with the cosmesis, weight, and function of the Dorrance hand. The vast majority (76%) of the children elected to continue wearing the experimental item at the conclusion of the study. The trend toward preference for the hand over the hook appears primarily related to a concern about cosmesis by this group of subteenage children. In an extensive evaluation of terminal-device use in 72 bimanual activities, no definitive trends emerged to indicate that the hook was measurably more functional than the hand or vice versa.

Seven children (21%) preferred their prior-worn terminal devices, six of which were hooks. The reasons cited for this preference were less effort to operate, greater durability, and a tighter grip, with improved prosthetic function. Two of these children were above-elbow amputees, and two had very short below-elbow stumps. The greater weight of the hand undoubtedly increased the effort requirements and limited the function of these children. However, it should be noted that the six children who preferred their prior-worn hooks comprised only 30% of the subsample of 20 who were hook wearers before participating in the study; 65% favored the Dorrance hand rather than the hook, and one child had no strong predilection for either the hook or the experimental hand.

One boy preferred the cosmesis of the Robin-Aids hand, feeling that it was more masculine in appearance and was a better size, being somewhat larger than the experimental hand. He found all other aspects of the two hands (function, weight, etc.) to be comparable.

Twenty children wore the hand for the six-month period without experiencing any mechanical difficulty. Thirteen children wore 15 different hands that malfunctioned at least once and had to be returned to the manufacturer for repair.

The majority of failures occurred at the attachment point of the active fingers and thumb, which resulted in excessive finger play, loss of three-jaw-chuck, or fracture at the metacarpophalangeal joints. During the course of the study, the manufacturer made various modifications within the hand mechanism, which served to minimize or eliminate these problems in subsequent hands.

The color, texture, durability, and stain resistance of the cosmetic gloves were considered satisfactory by the majority of children and parents. Negative comments in these areas were primarily related to poor glove durability (six children) and inadequate stain resistance (nine children). Since consistent records on the length of individual glove wear were not obtained, no definitive statement can be made regarding wear life of the gloves.

Based on the positive results of this study, the Dorrance Model 2 hand is a valuable addition to the armamentarium of upper-extremity prosthetic components.

-Ann Gorton

Preliminary Evaluation Of The Ambrl Porous Laminate Ptb Prosthesis

Despite the fact that the patellar- tendon-bearing (PTB) prosthesis has achieved a high degree of general acceptance, perspiration problems associated with the intimate fit of the impermeable socket have rendered the prosthesis subject to criticism.

For several years the U.S. Army Medical Biomechanical Research Laboratory (AMBRL) has been involved in the development of techniques for fabricating porous sockets which would allow some ventilation of the stump. The results of an earlier New York University evaluation of prostheses fabricated using a polyester porous laminate technique, completed in May 1965, indicated that this material did not offer a satisfactory combination of porosity, weight, and strength. Further development of the technique resulted in a new fabrication method involving an epoxy laminate, which was presented for evaluation in the spring of 1966 (Fig. 4 ).

Data were obtained on four successful wearers of conventional PTB prostheses, who were fitted with porous prostheses fabricated at NYU in accordance with instructional materials and guidance from the developer. The porous prostheses were worn for one month, then were covered with Saran Wrap to render them impermeable. After a month's wear in the nonporous state, the covering was removed. Thus, the subjects wore the prostheses under both permeable and impermeable conditions. At three months postdelivery, laboratory determinations regarding weight and porosity were conducted. Amputee reactions and stump conditions were recorded at each visit.

Results

All four amputee subjects reported a significant reduction in discomfort associated with perspiration when the porous prostheses were compared to their conventional PTB prostheses. Three noted a definite increase in discomfort following the application of Saran Wrap. None of the four subjects experienced difficulties related to the change from the lined socket of their conventional prostheses to the hard socket of the experimental prostheses.

The porous laminate was structurally adequate for the medium-weight individuals in the study, showing no signs of deterioration after six months' wear. Laboratory checkout procedures confirmed the retention of socket conformation. There was no evidence of dirt or lint clogging the pores to adversely affect the porosity of the sockets.

The porous prostheses were consistently lighter than the conventional prostheses worn by the subjects. In this limited sample, the average weight reduction was about 32%.

Prosthetic procedures involved in the fabrication as presented in the instruction manual provided by AMBRL were found to be consistent with and well within the scope of accepted prosthetic practice; no unusual equipment was necessary. Procedures for fabricating this porous epoxy laminate differ from those used in the polyester lamination system in two essential respects: (1) the utilization of Silastic Elastomer #385 and Foam Elastomer #386 to form the soft dis>tal end, and (2) impregnation of the Banlon and nylon stockinette substrata with a resin mixture consisting of epoxy EPON, Versamid, pigment, and methylene chloride. On average, fabrication of a porous limb took approximately two man hours longer than the time required for a conventional prosthesis.

One additional heavy subject (over 200 pounds) has been fitted for further study of the strength and durability of the porous laminate prosthesis, with satisfactory results to date. During the summer of 1967 a field study will extend the evaluation to a large sample of juvenile amputees.