Evaluation of synthetic balata for fabricating sockets for below-knee amputation stumps.

Executive Director, Committee on Prosthetics Research and Development, National Academy of Sciences—National Research Council. At the present time, most sockets for artificial limbs are made of a plastic laminate (usually polyester resin and Dacron) which has been molded over a modified replica of the stump. A replica of the stump is required because human tissues cannot withstand the temperatures generated by the exothermic reaction of the plastic as it cures. The replica is modified, using general rules established by research groups, in order to achieve a relationship between the stump and socket that is physiologically satisfactory, yet permits weight-bearing and provides stability. In addition, reliefs must be provided to accommodate bony prominences and any tender spots. A simple plaster-ofparis wrap will usually be too loose for normal use. Therefore, fabrication of plastic-laminate sockets with presently available materials involves at least the following steps (Fig. 1): (a) development of a female mold of the stump by wrapping the stump with plaster-of-paris bandages, (ft) casting a male model of the stump by filling the female mold with plaster of paris, (c) modification of the male model by trimming away plaster in selected areas and building it up in other areas when necessary, and (d) lay-up and cure of the plastic laminate. The average time required to make a hard socket below-knee plastic prosthesis is eight man-hours. It has been the goal of a number of research workers to find a simpler and less time-consuming method for fabricating satisfactory sockets for all levels of amputation. After many experiments involving a number of casting methods and a variety of materials, the Veterans Administration Prosthetics Center by 1961 had developed a technique for molding a socket of synthetic balata directly over a belowknee stump. The first successful results were achieved by using an air-pressure sleeve over a tube of synthetic balata, which had been softened by immersion in hot water (160 deg F) and then pulled over the stump (1,2) (Fig. 2).