The Syme's Amputation: A New Prosthetic Approach

Robert L. Romano, M.D. Joseph H. Zettl, C.P. Ernest M. Burgess, M.D.

This study was conducted under Contract No. V663P-505 with the Veterans Administration.

The vast majority of amputations performed in the Western world are for vascular insufficiency and of necessity are usually done through the shank or at higher levels. While few amputations are performed at the ankle or lower in peripheral vascular disease, the Syme's amputation is used frequently in trauma and particularly in revising congenital abnormalities in children. Whenever feasible, the Syme's amputation should be considered in preference to amputation at a higher level since it presents many advantages.

In this procedure the bone level is immediately above the ankle joint and the bone end is covered with tough plantar skin. The stump is designed for direct end-bearing and has been shown to withstand years of weight-bearing without breakdown. The long lever arm with resultant increased control and power is advantages, and the bulbous end gives increased stability in the prosthetic socket. Moreover, the stump is long and tough enough for weight-bearing without a prosthesis and short enough for application of a prosthetic foot.

For years attempts have been made to improve the surgical technique of the Syme's amputation to eliminate the bulbous stump end. This bulbousness reduces the cosmetic appeal of the prosthesis and is particularly objectionable to removal of the malleoli. This procedure does provide a slimmer stump, but reduction of the bulbous end also reduces socket stability. Moreover, some loss of the broad end-bearing characteristic of the stump is experienced. Ideally, it is better to retain the typical Syme's stump with its long lever arm, broad end-bearing base, and bulbous end for socket stability (Fig. 1 , Fig. 2 , and Fig. 3 ). This report describes an improved socket which makes this type of stump easier to fit.

Syme's Amputations in Children

First, reference should be made to the Syme's amputation as seen in the child amputee clinic. In our experience, most amputations of this type have been done for congenital abnormalities, primarily congenital absence of the fibula. We refer to the typical deformity with dysplasia of the entire limb, including complete absence of the fibula, shortening of the femur, shortening of the tibia (frequently with bowing), equinovalgus deformity of the foot, various tarsal and metatarsal anomalies, and a tight fibrocartilaginous band running from the proximal end of the tibia to the calcaneus. Most of these cases have had multiple surgical procedures, including heel-cord lengthenings, excision of a fibula remnant, tibial osteotomies, leg lengthenings, and epiphyseal stimulation. In all cases, leg-length discrepancies which, at the time of amputation, frequently exceeded three inches have been the end result. This length discrepancy continues to increase until maturity is reached.

There is general agreement that these children should not be subjected to repeated surgical procedures only to be fitted finally with a platform shoe buildup of poor cosmesis and poor function. Early Syme's amputation is the procedure of choice and should be done as soon as it becomes apparent that the inevitable outcome will be a leg-length discrepancy exceeding three inches, or a very deformed foot that cannot be maintained in a weight-bearing position.

The procedure is also frequently done in children with proximal femoral focal deficiency (Fig. 4 ). Because of the short thigh segment, the knee joint is located proximally and the foot is frequently as much as ten inches from the floor. Even though the foot may be normal it is of no value at this level, and in fact compromises bracing or prosthetic fitting. If a Syme's amputation is done, the patient can be fitted with a prosthesis of far better cosmesis and function.

The standard surgical technique varies somewhat in children but, as in the adult, careful attention is directed to the preservation of both the specialized subcutaneous tissue in the heel flap and the neurovascular supply. The talus and calcaneus are dissected out subperiosteally to avoid the calcaneal arteries. To avoid compromising the blood supply, dog-ears are never trimmed. Cartilage is removed from the tibia and the malleoli with a knife. Thus the epiphyses are maintained intact for further growth. In this way we obtain a stump that has the advantages of the adult Syme's amputation but is shorter and can be fitted more cosmetically (especially valuable in girls) because the wide end fits into the prosthesis at a higher and better level. Yet we still have the advantages of an end-bearing stump both with and without the prosthesis and a bulbous end that adds to socket stability.

The typical Syme's prosthesis of the past was made of either wood or molded leather riveted to a one-piece metal frame for structural strength. Both types retained the stump in the socket by means of an anterior lacing arrangement over a firm and usually molded leather tongue. Because of the design, all around total contact was not attained in most cases. A mechanical two-way ankle foot with toe break completed this prosthesis. In most instances, the resulting prosthesis was bulky, heavy, and uncosmetic. If attempts were made to reduce bulk and weight, early metal fatigue and breakdown of the steel frame occurred as a result of the high forces created by the dorsiflexion moment of the toe lever.

In 1954, with the availability of plastic laminates, the Canadian Department of Veterans Affairs introduced a perforated plastic-laminate Syme's prosthesis with a posterior socket opening. Subsequent modifications by the Veterans Administration Prosthetics Center, New York University, University of California at Berkeley, and others resulted in design improvements. Provision of a posterior or medial window (Fig. 5 ) in the socket facilitated stump insertion. The introduction of a modified SACH-type Syme's foot further decreased bulk and appreciably enhanced cosmetic appearance. However, creating the posterior or medial socket window openings weakened the structure of the plastic laminate. In many instances failures occurred just above the junction of the distal vertical and horizontal cut lines of the window opening. Epoxy resins reinforced with glass fibers and metal reinforcements in polyester laminate lay-ups provided only moderate improvements in durability. Also the attachments of the posterior socket segment and window replacements required retainers or strap fasteners that were occasionally noisy and always added extra bulk to the prosthesis.

In 1965 the University of Miami introduced a closed double-walled Syme's prosthesis with a flexible inner wall that expanded as the bulbous stump was inserted into the socket. The resulting prosthesis was light, durable, and more cosmetic than any of its predecessors. At our laboratory Syme's prostheses with expansible, flexible inner-wall sockets have been fitted with good results to patients with mature and stabilized stumps. Patients with very bulbous heel pads are not considered ideal candidates for this type of prosthesis because of limitations in amount of stretch provided by the flexible inner socket and its poor cosmesis. Furthermore, it was essential that the positive mold be extremely accurate since socket adjustments to the flexible inner socket cannot be made without damaging the socket. Thus, for a growing child or a patient with an immature, fluctuating stump that demonstrates atrophic or hypertrophic changes, a more suitable prosthetic socket design seemed necessary.

The New Syme's Prosthesis

The Prosthetics Research Study procedure for a closed Syme's prosthesis utilizes the basic principles of the flexible inner-wall socket by incorporating a removable insert liner constructed of Kemblo rubber and Silastic foam (Fig. 6 ). The liner in effect bridges the narrow portion of the stump just superior to the bulbous heel pad, and maintains a total-contact stump-socket relationship. For the very bulbous Syme's stump, the insert liner is slotted posteriorly three to four inches to allow insertion of the stump (Fig. 7 ). The exterior of the liner is then covered with a thin cast-sock prior to its insertion into the prosthetic socket (Fig. 8 and Fig. 9 ). The procedure results in a Syme's prosthesis to which repeated reliefs and adjustments to accommodate various stump changes can be made. Most patients achieve and tolerate total end-bearing with maximum proprioception. New patients provided with initial prostheses are fitted with partial end-bearing and proximal loading on the patellar tendon and medial tibial condylar flare. Excess tissue redundancy, pain or displaced heel pads as a result of poor surgery might require total proximal weight-bearing temporarily or permanently and thus lose all the inherent advantages of a good Syme's amputation. The cosmetic appearance of the prosthesis can be further enhanced by restoring the shape of the calf region with the aid of polyurethane foam (Fig. 10 ) prior to final socket lamination. We recommend the use of an exteriorized wood-keel-type Syme's foot which is included in the final lamination lay-up and improves cosmetic appearance.

Fabrication of the PRS Syme's Prosthesis

Cast and Modifications

In taking the cast for the PRS Syme's prosthesis, the principles of the premodified casting system are utilized. Bony prominences or sensitive areas are identified and relieved with appropriately shaped and skived felt relief pads attached to the stump. Pressure-tolerant areas of the stump are further emphasized by means of felt compression pads. Elastic plaster-of-Paris bandage is used to make the initial plaster wrap. Care is taken to maintain the heel pad centrally located over the cut end of the bone to avoid medial or posterior displacement. The patient bears partial weight on an appropriately elevated wood platform while the initial plaster wrap hardens. The elastic plaster wrap is reinforced with conventional plaster bandage and, with the patient standing with partial weight-bearing, lateral and anterior alignment reference lines are marked vertically on the cast with the aid of a carpenter's square. When the completed wrap has hardened it is bivalved with a cast saw and removed from the stump. After the positive cast has been prepared the vertical alignment reference lines on the negative wrap are transferred with an awl to assist in achieving the appropriate prosthetic socket-foot relationship during bench alignment.

The positive cast requires only minor modifications, mainly in the areas of the seams caused by the saw cut. A smooth finish is provided for the entire model with screen wire and finally with wet or dry Fabricut silicon carbide, 180 grit. The completed model is sealed with Hosmer-Lac, Ambroid, or equivalent, to prevent dampness in the plaster from affecting the inner PVA bag during lamination (Fig. 11 and Fig. 12 ).

The Socket Liner and Plastic Lay-up

Construction of the socket liner is basically similar to that of the standard PTB Kemblo insert. Noteworthy exceptions are:

  • In place of the customary horsehide leather, Naugahyde or Vibretta has been used successfully (Fig. 13 and Fig. 14 ). This material appreciably outlasts leather but it should be noted that the plastic does not absorb moisture which could contribute to problems of excessive perspiration in warmer climates.

  • Provision must be made for a posterior opening in the liner. The size of the bulbous distal stump determines the length of the opening which extends from the bulbous end to a point of equivalent diameter proximally to permit donning and doffing of the liner. After completion of the Kemblo rubber lay-up, the area between the two aforementioned reference points is bridged with a cardboard cylinder and secured by masking tape. The resulting space is filled with approximately 150 grams of a mixture of 50 per cent Silastic 386 Foam Elastomer and 50 per cent Silastic 388 Denture Release or equivalent (Fig. 15 ). The cured Silastic is sanded as required to achieve a tapered cylindrical sleeve which avoids excess bulk in the area of the concave neck (Fig. 16 ).

A PVA bag and vacuum are applied (Fig. 17 ) and standard procedures for fabricating a polyester socket are followed. Two layers of dacron felt and two layers of nylon stockinette are usually sufficient.

Bench, Static, and Dynamic Alignment Procedures

The previously described vertical-alignment lines transferred to the positive mold for reference are used for standard bench alignment (Fig. 18 ). In our experience the SACH-type foot with an external wood keel is the most satisfactory with respect to strength and cosmesis since it will be laminated into the prosthesis in the finishing process. The use of the PRS-Syme adjustable prosthetic unit is recommended since it permits rapid static and dynamic alignment changes (Fig. 19 ). With the foot-attachment bolt in neutral position, the concavity of the socket-attachment plate provides 10 deg. of plantar flexion or 10 deg. of dorsiflexion for a total foot adjustment range of 20 deg. Horizontal mediolateral slide adjustment of 7/16 in. in either direction for a total of 7/8 in. is provided. These adjustments are independent of each other.

After determining proper bench alignment, the prosthetic socket is fastened initially with glass filament tape to the socket-attachment straps. The use of 8/32 in. flathead machine screws and/or a polyester resin and microballoon mixture will secure the unit to the socket with sufficient strength to complete static and dynamic alignment.

Transfer and Finishing of Prosthesis

The foot and socket are appropriately secured in the UC-Berkeley transfer jig. The prosthetic alignment unit is removed. When a microballoon mixture has been used for socket-unit retention, it must be carefully heated for removal. The resulting space created between socket and foot is in., the thickness of the alignment unit. This space is simply filled with a fresh mixture of solka floc spheres and polyester resin, thus bonding foot and socket permanently to each other.

In cases where the calf size of the sound leg differs appreciably from that of the stump, polyurethane foam (Hosmer or Otto Bock) is used to achieve matched cosmesis, Also, the foot and socket junction is properly filled and shaped to blend smoothly.

The final lamination is done after removing the rubber sole and heel cushion from the wood keel of the Syme's foot. Two layers of nylon stockinette are usually sufficient for a standard laminate finish.

The resulting Syme's prosthesis is self-suspending and does not require an additional cuff-suspension system.

PRS Experience

In our experience twelve prostheses of the type described have been fitted to patients ranging in age from 1 to 82 years. One young man wore the prosthesis for a period of more than four years without evidence of skin irritation or breakdown. Stump atrophy resulted in occasional socket and liner adjustments but neither required replacement. The entire prosthesis was eventually replaced because of growth which no longer could be accommodated.

The disadvantage inherent in this system is the bulk added to the prosthesis as a result of the Kemblo-Silastic insert. Thickness of the insert is held to an absolute minimum by sanding. Because of the rubber liner, perspiration could also be a problem in hotter climates but has not presented difficulties in our experience to date.

Prosthetics Research Study Seattle, Washington

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