The Use of a Silastic Liner in the Syme's Prosthesis

Arthur L. Eckhardt, M.D. Harold Enneberg


The Syme's amputation has proven to be one of the most satisfactory lower-extremity amputations in the adult male. The main advantage of amputation at this level is the preservation of the heel pad which materially increases the amount of weight which can be borne on the end of the amputation stump. When leg-length inequality is not extreme, the amputee can ambulate without a prosthesis with little difficulty.

In children, a similar endbearing amputation stump can be achieved by performing an ankle disarticulation, which does not damage the distal tibial or fibular epiphyseal growth centers. The preservation of a long below-knee lever arm gives excellent prosthetic control and stability. Snug fitting of the socket around the narrower part of the limb proximal to the bulbous end provides excellent suspension when the stump is well seated. This construction usually does away with the necessity for providing any type of suspension about the upper end of the prosthesis. To allow the enlarged end of the stump to reach the bottom of the prosthetic socket, it has usually been necessary to make a "door" in the narrow portion of the socket. This "door" is then closed after the stump is seated.

In spite of the many advantages of the Syme's-type amputation and prosthesis, they have some undesirable features. The large dimensions of the distal end of the prosthesis where it fits around the bulbous stump present a poor cosmetic appearance. This is one reason a Syme's amputation is rarely performed on females. The "door" that allows the stump to pass into the distal end of the prosthesis disrupts its smooth contours as do the straps needed to secure the panel in place. Furthermore, although the long lever arm provided by this type of amputation provides excellent control of the prosthesis, it has the disadvantage that it places more stress on the prosthetic socket than does a conventional below-the-knee amputation. Because of this stress the Syme's socket must be made stronger and thicker than the usual below-the-knee socket, thus increasing weight and giving a bulky appearance.

In the Child Amputee Clinic at the Portland Shriners Hospital we have been experimenting with a silastic liner which is built into the socket of the Syme's prosthesis. By expanding this liner the bulbous distal stump can reach the end of the socket and thus the need for a "door" in the prosthesis is eliminated. The liner also provides total contact for the amputation stump, thereby providing excellent socket suspension. The prosthesis is stronger than the type requiring a "door" because of its cylindrical construction and does not necessitate an excessively thick laminate.

Fabrication

The negative cast of the stump is taken with alginate.* The plaster positive moid is prepared in the usual manner and is modified proximal to the bulbous end to ensure a snug fit (Fig. 1 and 2 ). A PVA (poly-vinyl-alcohol) bag is applied over the mold as a parting agent to prevent the resin from binding to the piaster.

In the fabrication of the socket, 1/2 ounce dacron felt, four lengths of nylon stockinette, and another PVA bag are used initially. The last PVA bag is

wrapped with plastic tape at a point about two-thirds of the distance toward the proximal end of the cast where its circumference equals the circumference of the bulbous stump (Fig. 3 ). This wrap must be tight enough to provide a seal. The PVA bag is then filled with "below-the-knee" silastic elastomer (#384) to this level. When the silastic has set, the tape is removed and the PVA bag is filled with 4110 laminae resin which impregnates the rest of the nylon stockinette. The outer PVA bag is removed and the concave area over the silastic liner is covered with a mixture of beeswax and paraffin (Fig. 4 ). Next, two more layers of stockinette are pulled over the entire model and laminated with 4110 resin. The vacuum lamination procedure is used throughout. When the laminate is cured, the wax is melted and drained out through a hole in the popliteal area of the socket leaving an air space around the silastic liner. A wooden keel and laminated foot are attached to the socket. The entire socket and foot is laminated again. The socket is then trimmed and smoothed, and is ready for use (Fig. 5 ). This prosthesis is essentially the same as the "balloon prosthesis" described by Mazet.1

This prosthesis has now been used in our clinic by five children (three boys and two girls) ranging from seven to fifteen years of age.

Case Histories

T.B. is a seven-year-old boy with a right ankle disarticulation (Fig. 6 ). He had previously worn a Syme's-type prosthesis with a suspension strap. The strap was needed because he had a minimal enlargement at the end of his stump and the socket could not be retained without some type of auxiliary suspension. He has worn his silastic-lined prosthesis for two weeks only. He has an excellent gait and has had no problems with loosening of the prosthesis when he runs and plays.

K.E. is a 15-year-old girl who has congenital shortening of the right femur and a right paraxial fibular hemimelia. A Syme's amputation was performed on the right lower extremity in 1960. She wore a conventional Syme's prosthesis until August, 1968, when she was fitted with a silastic-lined prosthesis. In spite of the fact that her knees are at different levels, she has a good gait. The liner prevents pistoning of the stump in the prosthesis. Since she began wearing the silastic-lined prosthesis she has worn out three liners. Fortunately, it has been possible to replace the liner without fabricating an entire new prosthesis.

Two other children, a girl 15 years and a boy 10 years, have worn silastic-lined prostheses for approximately five months. Both have an excellent gait and like the total contact aspect of the silastic liner. The girl is pleased with the improvement in cosmetic appearance.

R. T., a very athletic 15-year-old boy who has earned letters in basketball and football in high school. He is our one "failure." He found the prosthesis adequate for normal activities but did not have good control of the prosthesis when running and jumping. The liner allowed too much rotation of the stump during his participation in strenuous sports (Fig. 7 and 8 ).

Summary

In summary, we feel that there are advantages in using the Syme's prosthesis with a silastic liner. Its cosmetic appearance has been well accepted by our two female amputees. The total contact of the liner with the amputation stump has not caused any skin problems and has provided good socket suspension in most cases.

*This material gives a superior impression of the stump and when set is somewhat elastic so that the limb may be withdrawn without splitting the cast. It is. however, more expensive than plaster of Paris and does not permit palpation of the stump to locate the heel pad during the casting process.

Arthur L. Eckhardt, M.D. and Harold Enneberg are associated with the Child Amputee Clinic, Shriners Hospital" Portland, Oregon

References:
1. Mazet. R. Jr., "Syme's Amputation," J. Bone and Joint Surg., 50-A: 1549 1563, 
December 1968.