Development of Layered "Onionized" Silicone Sockets for Juvenile Below-Elbow Amputees


The Hugh MacMillan Medical Centre, with Canada's largest child amputee group, was the site of a new project. Silicone rubber elastomer sockets with successively laminated liners (Fig. 1 ) were designed and fabricated for children wearing myoelectrically controlled below-elbow prostheses. Whey amputation limb growth necessitated removal of a liner, fit and comfort coup be reestablished readily.


Twenty children, aged 5 to 14 years, participated in a two-year study. All have below-elbow amputations between a third to a half of the length of the sound side. Patients were divided into two groups matched as closely as possible for sex and age. Group A was assigned to the layered socket and Group B to the standard hard, polyester resin socket. All sockets were the Northwestern design, with the medial and lateral brims terminating above the humeral epicondyles for suspension.

Fabrication of the layered socket required a plaster wrap of the amputation limb which served as the basis for the positive mold for the silicone socket. In the laminating process, six pieces of stockinette, sewn on one end, were used. Lamination was performed so that the first and second liner consisted of one layer of nylon tricot each. The third lamination had four layers of tricot. Polyvinylacetate film was the separator between each successive lamination. When the multilayered laminations were fully polymerized, they were trimmed along the brim line.

A short pipe was attached to the distal end of the socket. At the other end of the pipe a 500 to 900 gram (17.5-31.5 oz) weight was added, depending on the size of the patient, to simulate the overall anticipated weight of the finished prosthesis. The weighted socket was placed on the patient, and fit, comfort, effectiveness of suspension, and range of elbow motion determined. Only when the socket check proved satisfactory was the final fabrication completed, using standard procedures. Because of the multiple lay-up, fabrication time was approximately two hours, as compared with the one hour customary for a rigid socket. The initial total cost for the prosthesis with layered socket was essentially the same as for a standard prosthesis.

For children fitted with the layered socket, circumferential and axial growth of the amputation limb and its effect on prosthetic fit were charted (Fig. 2 ).

For those fitted with conventional sockets, the average number of socket modifications required because of growth were posted for each child, in addition to the average interval between modifications and the annual cost.

Results and Discussion

The layered socket design achieved goals established at the initiation of the project. Comfort and prosthetic wearing tolerance were excellent because silicone rubber elastomer adjusted easily to the wearer's amputation limb. Elbow range of motion was greater because of the flexibility of the silicone. Patients reported that the flexible sockets were more comfortable than rigid ones and continued to wear the new sockets even when they became too tight. Parents could remove a liner when the child felt the present socket was excessively snug, and could reinstall a liner that had been removed previously to accommodate any loss in girth of the amputation limb. Seven children wore the layered sockets for the entirety of the project; two continued to use the original three socket layers 19 months after original fitting. Three required liner removal, an average of 6.6 months after prosthesis delivery. Two others needed forearm relamination, probably because the original forearms were too thin. Of the eight control subjects who required growth adjustments, these averaged approximately two per year.

Average annual cost for the layered sockets was $143, as compared with $466 for rigid sockets. Thus, the new approach proved nearly three times more cost effective than the conventional hard socket, even though fabrication requires one hour more and makes greater demand on the prosthetist's laminating skills. Clinic visits were less frequent because parents could remove or reinstall liners readily. The largest single expense was associated with relaminating forearms, costing $600 each. Flexible sockets are virtually indestructable, an important economic factor in management of vigorous youngsters.

Silicone itself is inert and did not cause skin problems. One adolescent, however, withdrew from the study because of allergic reaction to a sealant (acetic acid-based bathtub caulk) used to reseal the electrodes into the socket wall after a liner had been removed. The two youngest participants, both 5 years old, complained that the layered sockets were too bulky. They were refitted successfully with rigid sockets. Silicone sockets are difficult to modify, not lending themselves to rapid alteration. If the socket does not fit and suspend well, the prosthetist should make a new one. For children whose first liners were removed within two months of prosthesis delivery, it is likely that shortcomings in the basic shape of the socket existed.

The overall success of the project suggests that optimum candidates for the layered, "onionized" socket are children old enough to accept a slightly thicker socket wall.


We appreciate the support received from the National Health Research Development Programme, Health and Welfare, Canada, Project #6606-2115-55.

*The Hugh MacMillan Medical Centre, 350 Rumsey Road, Toronto, Ontario M4G 1R8