A Silastic-Lined Knee-Disarticulation Prosthesis

REES R. SWEITZER, B.A.


A recent issue of Newsletter . . . Amputee Clinics on knee-disarticulation amputations and prostheses mentioned the increasing use of Silastic-lined Syme's prostheses by various responding clinics. Phelps and Stanford gave excellent coverage of the prosthesis for the Syme's amputation in the October 1971 Inter-Clinic Information Bulletin , These authors reported that similar fabrication procedures could be applied in the fitting of knee-disarticulation amputees. It has been our finding also that with only minor modifications the technique is equally valuable for other disarticulations of both upper and lower limbs.

The procedure described in this report is used for all disarticulation levels mid-limb and distal with a knee-disarticulation case used as the illustrative example.

Cast Preparation

A positive model ( Fig. 1 ) is obtained in the usual manner. If the circumference of the area just proximal to the bulbous end is less than 80 percent of the maximum dimension, the cast should be built up to the 80-percent proportion. The posterior and medial cast surfaces are not built up, thus providing two rigid walls in intimate contact with the stump.

A distal pad of 1/4-in. soft-cell crepe or similar materia' is added to the cast and a PVA sheet is pulled over the pad, or lacquer is applied ( Fig. 2 ).

Socket Lay-Up

A lay-up of two thicknesses of nylon stockinette is used ( Fig. 3 ), and a distal PVA cap is applied and taped in place. In those cases where the circumference of the "neck" of the (unmodified) cast is less than 85 percent of that of the bulbous end, a third layer of nylon stockinette should be added.

A PVA bag is installed and the level to which the elastomer is to be applied is marked. This level is the point at which the circumference of the proximal stump is equal to that of the bulbous end. This portion of the socket is then impregnated with RTV 384 Silastic elastomer ( Fig. 4 ).

Following removal of the PVA bag, a wax build-up is applied to increase the diameter of the "neck" of the prosthesis so that the stump will pass through. Two surfaces-the medial and posterior- are left without build-up ( Fig. 5 ).

Lamination

Two more layers of nylon stockinette are now applied and laminated with a mixture of approximately 85-percent rigid and 15-percent flexible polyester resin ( Fig. 6 ).

Outside knee hinges are typically used with our knee-disarticulation prostheses and the upper bars of appropriately sized hinges are now placed in position ( Fig. 7 ). The distal end of the socket is contoured about the axes of these hinges. Two additional layers of nylon stockinette and a PVA bag are pulled over the model ( Fig. 8 ), and the whole lay-up is laminated with polyester resin.

Shank Installation and Finishing

Following lamination the selected shank is installed. Fig. 9 depicts a prosthesis with an adjustable pylon*, while Fig. 10 shows the leg finished with VS-400 vinyl foam as described by Mr. William F. Sauter of the Ontario Crippled Children's Centre**.

* This pylon is now under evaluation and will be described in more detail in a subsequent issue of the Inter-Clinic Information Bulletin, together with the results of the clinical study.

** A description of Mr Sauter's technique is carried as a separate article in this issue of the Inter-Clinic Information Bulletin (page 10)-Editor.

References:
Eckhardt, Arthur L., and Harold Enneberg, The use of a Silastic liner in the Syme's prosthesis. Inter-Clin. Information Bull., 9 :6:1-4, March 1970.
LeBlanc, Maurice A., Elastic-liner type of Syme prosthesis: basic procedure and variations. Artif. Limbs, 15 :1:22-26, Spring 1971.
Marx, Herbert W., An innovation in Syme's prosthetics. Orth. and Pros., 23 :3:1 BIOS, September 1969.
Mazet, Robert, Jr., Syme's amputation, a follow-up study of fifty-one adults and thirty-two children. J. Bone and Joint Surg., 50-A : 8:1549-1563, December 1968.
Meyer, Leslie C, Harry L. Bailey, and Dewey Friddle, Jr., An improved prosthesis for fitting the ankle-disarticulation amputee. Inter-Clin. Information Bull., 9:6 :-11-15, March 1970.
Newsletter . . . Amputee Clinics, CPOE, NAS, IV:4, August 1972.
Phelps, Marcus E., and James W. Stanford, Fabricating an expandable inner-socket prosthesis. Inter-Clin. Information Bull., 11 :1:7-10, October 1971.
Ruder, Karl H., A different approach to suspension of Syme's or knee bearing prosthesis. The Canadian Ortho-Pros., 5 :4, Fall 1971.
Sarmiento, Augusto, Raymond E. Gilmer, Jr., and Alan Finnieston, A new surgical-prosthetic approach to the Syme's amputation, a preliminary report. Artif. Limbs, 10 :1:52-55, Spring 1966.