Fabrication Procedures for the Open-Shoulder Above-Elbow Socket
C. A. McLaurim, P. Eng. *
W. F. Sauter, CPO *
C. M. E. Dolan, M.S. *
G. R. Hartmann, CPO *
The Open-Shoulder, Above-Elbow Socket is a new design that offers several advantages over others. Unnecessary parts of the socket have been eliminated, particularly from the deltoid area. Use of this simplified socket in combination with careful fitting of the essential areas provides a prosthesis of less bulk and contact with the skin, and yet one with greater stability and mobility. Fig. 1 - Fig. 2
The two critical features of the open-shoulder, above-elbow socket are shown: the axillary yoke for stabilization of the proximal end, and the distal ring for stabilization of the distal end of the socket with respect to the stump. These two parts of the socket are all that need to contact the stump; the remainder of the socket is needed only for structural integrity. Fig. 3
The relationship of the socket to the skeleton is shown. Note that the anterior proximal extension fits medially to the humeral head, just beneath the clavicle, covering the coracoid process of the scapula. The medial edge is flared to conform with the chest wall.
The posterior proximal edge extends up to but not over the ridge of the scapula. It may extend further medially than the anterior extension, but normally not beyond the center of the scapula. The anterior and posterior extensions of the socket should be flexible, ideally with flexibility graded from nearly rigid in the socket proper to quite flexible at the proximal medial edge of the extensions, this being accomplished by a progressive reduction in layers of stockinet from distal to proximal areas. The lateral opening of the socket follows the natural line of the deltoid muscle group. It normally does not extend distal to the level of the medial brim of the socket, and in short stumps it may be considerably proximal to that level. Fig. 4 - Fig. 5
The medial brim of the socket is essentially straight in the anteroposterior plane. It is not thicker than 1/4 in., and has a well-rounded edge. Excessive thickness is likely to cause discomfort from pressure on the nerves that are medial and slightly anterior to the humerus. Generous radii or curves are essential in order to flare the straight medial brim into the anterior and posterior extensions.
The proximal portion of the socket is elliptical in cross section, with a flat medial wall. Between this point and the elbow turntable, the cross-sectional shape gradually changes from that of the flattened ellipse to a circle. Fig. 6
There are no special preparations required in casting the stump. A protective axillary "apron" should be used. Necessary measurements are the stump length, the stump circumferences at 2-in. increments beginning at the axillary level, and the length of the segments of the contralateral limb.
To provide a smooth cast requiring the least modification, a three-step cast-taking procedure is recommended: an anteroposterior (A-P) wrap, a mediolateral (M-L) wrap, and final cast shaping. Three layers of plaster bandage, at least as wide as the stump M-L diameter, are used. The slabs (splints) should be long enough to allow a 2-in. overlap at the top of the shoulder. The first wrap (A-P) is applied from back to front, fitting well medial to the acromion. Fig. 7
The M-L wrap is applied before the A-P wrap begins to set. One end of the plaster bandage should be draped over three tongue depressors, which are then held in the axilla snugly but not uncomfortably tightly while the rest of the bandage is draped over the end of the stump and up the lateral side. Fig. 8
To ensure adequate covering of the anterior and posterior proximal extensions, an extra slab of plaster may be used. The wrap is then smoothed gently, and the final shaping is obtained by placing the hand as illustrated. Note that the stump is held in the adducted position, thereby compressing the stump mediolaterally. The thumb is placed anterior to the shoulder joint, with the fingers posterior to the joint, over the scapula, to ensure a snug fit in the anteroposterior direction. Typically, the thumb and index finger will lie along the distal portion of the deltoid bulge. For a large amputee, it may be necessary for another technician to assist by holding the tongue depressors while the A-P shaping is performed. This position of the stump is maintained until the plaster wrap is set. Fig. 9
Before removing the wrap, plumb lines should be drawn on the wrap on the anterior and lateral surfaces, with the stump in a relaxed position. The outlines of the proximal brim of the socket should also be marked. Fig. 10
The plaster wrap is then removed from the patient, and the positive cast is poured in the usual manner with a metal pipe inserted as a mandrel. The markings of the wrap are transferred to the cast by means of a sharp awl before the wrap is removed. The lines indicated by the awl markings are drawn in on the positive cast after the wrap is removed.
The cast is trimmed in any areas showing ridges and in the axillary area, where a smooth radius is required. The contours of the cast are then gently smoothed and treated with a suitable separating agent, prior to lamination of the socket. Fig. 11
The permanent socket is laminated with conventional polyester resins, using a mixture that is approximately 50% flexible and 50% rigid. The socket is trimmed according to the principles described on pages 47-48.
A typical completed open-shoulder, above-elbow socket is shown. Fig. 12
Although other harness patterns can be used, the illustration depicts the pattern that is currently used and recommended by Ontario Crippled Children's Centre. This type of harness is more comfortable in the opposite axilla than is the figure-eight type. The actual position for fastening the elbow lock control strap and the control strap may be varied somewhat from that shown in the illustrations, following the principles of conventional shoulder-saddle or chest-strap systems. - Fig. 13
Slight modification of the standard figure-eight harness adapts that pattern to the open-shoulder socket. Fig. 14
Several successful fittings have been made utilizing San Splint* sockets, prefabricated in a series of standard sizes. The advantage of this material is that it can be heated in warm water to a temperature of 140 deg F and then reshaped on the stump to provide an accurate, individual fit. The material also has a satisfactory degree of flexibility, so that a comfortable fit may be maintained as the stump is moved to various positions. The distal end of the socket, after trimming for correct length, can be attached directly to the metal elbow turntable, using epoxy paste. The paste is applied to the turntable, and the roughened distal end of the socket, heated locally to 140 deg F, is placed over the turntable. A hose clamp or flexible electric tape will hold the socket firmly in place. Room-temperature vulcanizing Silastic foam* may be injected to provide total-contact distal fit.
- Anderson, Miles H., Harness and control systems, Chap. 9 in Manual of upper extremity prosthetics, 2nd ed., William Ft. Santschi, Ed., University of California, Los Angeles, 1958.