An Improved Prosthesis for Fitting the Ankle-Disarticulation Amputee

Leslie C. Meyer, M.D. Harry L. Bailey, M.D. Dewey Friddle, Jr., C.P.O.


In the management of children with congenital anomalies of the lower extremities we have followed the accepted principle of delaying surgical conversion until absolutely certain that it was desirable. When it was obvious that fitting would be enhanced by surgical removal of a foot, this clinic has used ankle-disarticulation applying a modification of the Syme technique.1

The advantages and disadvantages of this amputation have been well described elsewhere and will not be repeated here. Briefly, the surgical technique consists of a standard Syme's skin flap with disarticulation of the ankle and transection of the malleoli at the level of the articular surface of the tibia. No attempt is made to reduce the flare of the malleoli in the mediolateral diameter. Following skin closure the heel pad is usually secured to the under-surface of the tibia by a large K wire which is passed directly through the center of the pad into the center of the articular surface of the tibia.

A well-padded plaster-of-Paris wrap is applied. The cast is changed in two weeks; the pin is removed; and a plaster pylon prosthesis, which will allow weight bearing, is applied. Fitting of the definitive prosthesis is generally accomplished in six weeks. Originally we fitted this stump with a standard Canadian-type prosthesis with a removable medial "window." This method of fitting proved to be satisfactory although cosmetically it left much to be desired, particularly in girls.

New Socket Designs

Sarmiento, Gilmer, and Finnieston,2 and most recently Marx,3 have described fabrication techniques for Syme's prostheses utilizing a silicone elastomer in the fabrication of the inner wall of the socket. For the past two years we have been fitting these patients with a double-wall socket containing a silicone elastomer "window." Our technique allows for the passage of a bulbous disarticulated stump without the necessity of the unsightly removable "window." The "window" in a standard Canadian prosthesis normally reduces the strength of the prosthesis, and some additional strength has been obtained by our method of fabrication. This method has provided adequate suspension and excellent cosmetic appearance, and there have been no major maintenance problems.

A stump of ideal length will allow positioning of the bulbous distal end of the stump within the double-wall socket at a level which permits utilization of a standard SACH foot, thus achieving a good cosmetic result, if at all possible, the stump should be of sufficient length to permit ambulation without the prosthesis. The procedure therefore lends itself well to conversions of congenital malformations where some atrophy and shortening already exist. In the juvenile traumatic amputee, where insufficient leg-length discrepancy exists, a properly timed epiphysiodesis of the proximal tibia is indicated.

Fabrication

Before beginning construction of the prosthesis, the prosthetist must determine the size of the window which will be built into the socket wall.

The width of the window usually approximates the maximum diameter of the distal end of the stump. The length of the window is determined by the length of the narrowest part of the stump, which we call the isthmus. The proximal boundary of the window is located at a point where the diameter of the proximal stump equals the diameter of the bulbous end. A preformed wire oval of the desired width and length is selected (Fig. 1 ). This oval is positioned on the mold to coincide with the most bulbous portion of the stump end. In most cases this has been on the medial side. It is sewn to the four layers of stockinette which have been placed over the positive mold (Fig. 2 ). The oval now serves as a reservoir for the 384 elastomer (Dow Chemical Co.) (Fig. 3 ). We recommend strongly that this material be vigorously rubbed into the underlying stockinette so that it becomes completely dispersed through the filler material (Fig. 4 ). A sheet of PVA is pulled tightly over the elastomer (Fig. 5 ) and is held firmly around the mold until the elastomer is firm (Fig. 6 ). The sheet of PVA is removed, and another stockinette is placed over the original layers (Fig. 7 ), followed by a PVA sleeve (Fig. 8 ). The plastic-laminate inner socket is then poured and molded in the usual fashion (Fig. 9 ). The wire oval is removed by sanding down to it. The unfinished prosthesis is shown in Fig. 10 .

If the fit of the prosthesis is judged to be satisfactory, a beeswax buildup is placed over the window to provide space for the elastomer to expand. Two layers of stockinette are then applied and laminated again in the usual fashion, covering the elastomer window and hiding it from external view. The beeswax is removed by melting and draining through a quarter-inch hole drilled in the external wall. The window remains plainly visible inside the socket (Fig. 11 ). A completed prosthesis is shown in Fig. 12 A/B . The elastomer window allows the bulbous end of the stump to pass through the socket, and once past the window the stump is held firmly within the prosthesis by the spring action of the elastomer. No additional suspension of the prosthesis is necessary.

Our series consists of 15 patients (six females and nine males) fitted with 17 prostheses (two bilateral cases). Table 1 presents the age and diagnosis for each patient. Fig. 13 shows patient number 6 in his completed prosthesis.

The follow-up on this series is not long. However, we feel it is of sufficient duration for us to conclude that this method of fabrication has merit.

Leslie C. Meyer, M.D., Harry L. Bailey, M.D. and Dewey Friddle, Jr., C.P.O. are associated with the Shriners Hospital for Crippled Children Greenville, South Carolina

References:
1. Syme. J., "On Amputation at the Ankle Joint," London and Edinburgh Monthly Journal of Medical Sciences, 3:93, February 1843.
2. Sarmiento, A., Gilmer, Jr., R. E., Finnieston, A., "A New Surgical-Prosthetic Approach to the Syme's Amputation, A Preliminary Report," Artificial Limbs, 10:1:52-55, 1966.
3. Marx, H., "An Innovation in Symes Prosthetics," Orthotics and Prosthetics, 23:131 138,1969.