A Fitting for the Unilateral Below-Elbow Amputee with a Dislocated Radial Head.

Carman Tablada, C.P. Susan Clarke, B.S., O.T.R.


This work was supported by a grant from the Maternal and Child Health Service, Department of Health, Education, and Welfare.

In recent years the staff of the Child Amputee Prosthetics Project at the University of California at Los Angeles has been concerned with the difficult fitting problem presented by the child with a short-below-elbow amputation (congenital partial hemimelia) and a dislocated radial head. The clinical picture presented is that of a short stump, prominent radial head, and excessive hyperextension at the elbow3 (Fig. 1 ). When the child is fitted with a conventional short-below-elbow prosthesis, two major problems arise (At the UCLA Child Amputee Prosthetics Project single-pivot rigid hinges are not used in conventional below-elbow fittings. The hinge consists of distal extensions from a plastic humeral cuff which are riveted to the socket. Use of a .030-in. spacer during the riveting provides an attachment which permits the straps to pivot on the socket.). First, the stump tends to "pop out" of the socket as the child's elbow goes into hyperextension. Second, the extended stump may rotate in the socket and remain rotated as the child flexes his elbow as the prominent radial head prevents the child from derotating his stump (Fig. 1 -B). Although a Munster-type fitting solves these two problems, this prosthesis has not been satisfactory in our experience because of the limited range of elbow motion provided and its short life when applied to an active child1,2.

Design criteria for our new fitting procedure for the short-below-elbow amputee with a dislocated radial head were that the prothesis should:

  • Prevent hyperextension of the elbow.
  • Contain the radial head comfortably.
  • Allow for moderate growth changes
  • Allow functional freedom at the elbow.
  • Provide suspension and terminal-device control.

Standard socket fabrication and suspension procedures were modified to meet these criteria. A high socket brim which cups the olecranon and encases the epicondyles prevents hyperextension of the elbow by limiting elbow extension, the brim acting as a stop when it reaches the distal posterior humerus. Accommodation for the protruding radial head is made within the proximal lateral area of the socket.

If the overall length of the prosthesis permits, a 1/2-in. (12.5 mm) extension of the socket will accommodate moderate linear stump growth. Harness alignments for growth can be made by letting out the control-attachment strap of the figure-9 harness.

Primary suspension of the prosthesis is by means of a full cuff, with a fully adjustable Velcro closure. Secondary suspension is provided by the socket and harness/control cable system. The terminal device is controlled through the figure-9 harness (Fig. 2 ).

Fabrication

In typical fashion the fabrication of this prosthesis begins with measurements and casting. The usual sound-side measurements are taken. The length of the stump is measured and circumferential measurements are made at the bicubital fold, at mid-stump, and distally, with the stump flexed at 90 deg. The socket is designed to provide maximum stump-lifting power at this angle. The forearm will be preflexed to establish the desired maximum flexion angle. The circumference of the mid-third of the humerus is measured to establish the circumferential dimension of the full cuff.

The casting is a two-part procedure. Elastic plaster-of-Paris bandage is used routinely. The first part of the plaster wrap encompasses the bicubital fold and the olecranon, extending proximally over the epicondyles and distally to approximately 1 in. (2.54 cm) beyond the bicubital fold. Four to six layers of plaster bandage are used. While the plaster is still wet the patient is instructed to flex his elbow as far as he can. The wrap should be snug but not tight, as this would restrict the patient's elbow flexion. If necessary, the prosthetist can assist the patient in maintaining the elbow in flexion until the plaster has set. When the plaster has set the patient is instructed to extend his elbow as much as he can while the prosthetist prevents distortion of the wrap around the elbow. The second part of the plaster wrap encompasses the remaining portion of the stump. This is done in the conventional manner and allowed to set.

The initial portion of the wrap has predetermined the socket trim line. Once the positive mold has been poured, only minor modifications should be necessary. The circumferential measurements of the positive mold should correspond to those of the stump. A 1/4- to 3/8-in. (6.3 mm to 9.4 mm) buildup is made over the olecranon. The cast should also be built up to provide adequate relief for any other bony protuberance on the stump, especially the radial head. The anterior brim area on the positive mold will probably have a very sharp curve as a result of the patient flexing his elbow during the casting. This sharp curve can be filled in with plaster and blended into the anterior surface of the positive mold. As previously indicated, a 1/2 in. (12.5 mm) buildup is added to the end of the cast to allow for growth when the overall length of the prosthesis makes this addition possible. The socket is then laminated in the usual manner.

In forming the forearm, a cardboard cone is placed over the end of the laminated socket in whatever amount of forearm preflexion is desired (10 to 30 deg.). An adequate amount of light rigid polyurethane foam is mixed and poured into this cone and allowed to set. The remainder of the prosthesis is finished in the conventional manner. At the time of the fitting, the socket trim line will be established 1/2 in. (12.5 mm) higher than the epicondyles on the medial and lateral aspects. Posteriorly, the socket will extend 1/2 to 3/4 in. (12.5 mm to 18.7 mm) proximal to the apex of the olecranon and anteriorly right up to the bicubital fold. During the fitting the patient should be asked to flex and extend his elbow fully at which time any areas of impingement should be relieved. In every case the material used for the full cuff has been polyethylene and Velcro has been used for the closure. The uprights which attach the cuff to the socket are fabricated of 1/2 in. (12.5 mm) dacron webbing, triple layered and sewn together.

The attachment points of the straps to the socket are determined in the usual manner by using sharp outside calipers to determine the approximate center of rotation of the elbow joint. The polyethylene cuff is cut according to the humeral measurements previously taken, plus 1 to 1 3/4 in. (2.54 cm to 4.41 cm). This overlap facilitates the Velcro closure. The dacron-webbing uprights are attached to the socket. The socket and cuff are then put on the patient and the point of attachment to the cuff itself is found by arranging the dacron uprights so that they lie along the mid-shaft of the humerus and parallel to each other. The dacron-webbing uprights are attached to the cuff by two rivets on each side. The crossbar hanger and retainer plate are attached in the usual manner. An axilla loop or figure-9 harness has been used in all cases (Fig. 3 ).

Results

To date 15 prostheses using all or part of the design described have been fitted to 11 patients ranging in age from 5 to 18 years. Four children with short-below-elbow amputations and dislocated radial heads have been fitted with 7 prostheses. The average life of the prostheses has been 20 months with a range from 13 to 30 months.

The fittings have met all of the design criteria. During the functional evaluation and periodic follow-up visits a number of additional advantages were revealed. None of the children required major harness adjustments during the life of the prosthesis. The axilla loop remained comfortable in all cases and the parent or child, following brief instruction from the therapist or prosthetist, was able to adjust the control-attachment strap to allow for growth. A number of children also experienced greater freedom of arm movement during gross play (Fig. 4 ). This was attributed to the fact that the stump obtained a better purchase on the socket which allowed them to move their limb through its range without having to maintain their elbow in active flexion to retain the socket on the stump. The girls preferred the figure-9 harness to the standard figure-8 because of the improved cosmesis.

Because of these additional advantages, three children with short-below-elbow amputations and normal elbow joints were fitted. None has outgrown his prosthesis at this time, the longest period of fitting being 23 months. Maximum elbow flexion angle allowed by the 10 below-elbow fittings averaged 111 deg. with a range of 100 to 125 deg. Two of the children with dislocated radial heads have limited flexion due to the abnormal elbow joint. Three wrist-disarticulation amputees and one long-below-elbow amputee have subsequently been fitted using the full cuff-suspension and axilla-loop control system with standard socket fittings. This fitting was selected because of the simplicity of harnessing which provided both better cosmesis and a reduced number of trips to the prosthetics shop for harness adjustments. The range of motion at the elbow and life of each prosthesis were the same as those reported for the previous fittings.

Summary

A new type of prosthetic fitting has proved very successful for the child with a short-below-elbow amputation and a dislocated radial head. The problem of stump "pop out" and rotation in the socket has been controlled, the radial head has been retained comfortably in the socket, and a functional elbow range has been maintained. The life of the socket has been equivalent to that achieved with standard short-below-elbow fittings. The additional advantages of simplified harness adjustments, greater stump purchase on the socket, and a more cosmetically acceptable harness have broadened the range of patients who can benefit from all or part of this fitting. The range now includes all levels of below-elbow amputations.

Child Amputee Prosthetics Project University of California Los Angeles, California

References:
1. Epps, Charles H., Jr., and John H. Hile, Experience with the Münster-type below-elbow prosthesis, a preliminary report. Artif Limbs, 12:1:20-24, Spring 1968.
2. Friedmann, L., Should the Münster below-elbow prosthesis be prescribed for children? Inter-Clin. Inform. Bull., 11:7:7 15, April 1972.
3. Kruger, Leon M., and Nicholas R. Breyan, A study of radial-head dislocation in children with transverse partial hemimelia of the upper limb. Inter-Clin. Inform. Bull., 10:1:1-4, October 1970.