The Syme Prosthesis Revisited
William Doyle, CP
Jerry Goldstone, MD
Dave Kramer, PT
ABSTRACT
Surgically successful Syme amputation.
have often been followed by use of less
successful prostheses. A unique design
for medial-opening Syme prostheses
has been developed to address issues of
comfort, flexibility, strength, lightness
and durability. Parallel goals of reducing fabrication complexity, and therefore time, as well as providing ease of
adjustment were also achieved.
The design employs carbon graphite
material in conjunction with a construction technique that is compatible with
commonly used plastic fabrication
methods. The procedure is designed to
be readily adaptable to advances in materials technology. This article details
the fabrication procedures for this medial-opening Syme prosthesis.
Key Words: SYME amputation, ankle amputation; below-knee prosthesis
Introduction
The Syme technique of amputation has
existed since 1842 (1). Several excellent monographs have been written
concerning the initiation of the technique and its subsequent development
(1-5). Syme referred to his surgery as a
disarticulation at the ankle affording
ease of execution, less risk to life and a
comfortable residual limb (2). "A successful Syme amputation ensures for
the patient a mobility and independence not accorded to any patient with
an amputation at a higher level" (3).
In spite of these advantages, surgeons have been reluctant to perform
this operation. One cause for this hesitancy may have to do with the manufacture and use of the prostheses fitted
afterward (6). These prostheses are often less than satisfactory, especially
when compared to the dynamic potential known to exist in the Syme residual
limb. Prosthetic results after a BK amputation, although not as spectacular,
have been more predictable.
This article will describe a Syme
prosthesis and fabrication method used
in five prostheses. Patient activity levels varied from a bilateral moderate
walker to a jogger and racquetball enthusiast. The participants reported the
technique provided significant advantages. Attention was given to the needs
of the prosthetist for a method that afforded not only economy of time and
materials but also a simple technique
compatible with a variety of prosthetic
designs and configurations.
Background
The Syme procedure has several distinct prosthetic advantages over standard below-knee amputation levels:
Proprioception: The level of sensation is much closer to the ground than
for the below-knee amputee. The tissue that is preserved is constructed by
nature to bear weight and to deliver
sensory feedback from walking (2).
Control: Since there is much more
surface area and a longer lever arm, the
amputee has considerably enhanced
control of his/her movement (7).
Suspension: The typical Syme prosthesis is self-suspending. It does not
need a strap or belt. As a result, there
is little or no "pistoning" of the prosthesis during the transition from swing
phase to stance phase. This is a significant advantage. It makes the prosthesis
seem much more a part of the person
while increasing his/her self-assurance
and activity level.
Weightbearing Options: There are
three choices of weightbearing configurations in the Syme prosthesis:
- Distal: the preserved heel pad is
used to bear body weight (8).
- Proximal: the PTB characteristics of
the upper socket bear body weight while
unloading the distal surface (9,10).
- Shared: various percentages of
body weight are shared between the
proximal and the distal socket areas to
accommodate the patient's needs (8).
In spite of these prosthetic advantages, this very functional type of amputation surgery has waxed and waned
in popularity for distinct surgical and
prosthetic reasons.
Concerning Syme's surgical technique, Harris very strongly states: "No
matter how many Syme's stumps may
be examined to ascertain the results,
the conclusions will be misleading unless the technique of the operation is
known for each case. If the basic principles have been observed, and if the operation has been performed properly,
the result is an assured success. If any
of the fundamental principles have
been disregarded, the result may be
unsatisfactory, and it may not be possible to improve it" (2).
Primary among the prosthetic obstacles are: the intricate processes necessary to make the prosthesis, difficulty
of fitting (often due to the above processes), frequent structural failures and
poor cosmesis.
Several types of prostheses are fabricated for the Syme amputee, including
(see Figure 1
):
- Plastic prostheses with soft insert
liners that provide suspension by
means of compressible section in the
prosthesis wall or in the insert itself
(10,11).
- Plastic prostheses with a built-in
air chamber and bladder. The latter expands upon entry and then rebounds to
grip the residual limb and thus suspend
the prosthesis (11,12).
- Leather sockets usually with eyelets and lacing to allow entry and then
suspension when tightened. They have
metal uprights or a plastic "half socket." Some are articulated (5,10).
- Plastic prostheses with medial-opening "windows" that provide a
mode of entry and when closed provide
suspension (9,10).
- Plastic prostheses with posterior
removable sections, either a half-section hinged at the distal end or a
window. These sections provide a
means oof entry and when closed, suspend the prosthesis (8).
Method
The medial-opening Syme prosthesis
was proposed for improvement. The
goal was to construct a limb that incorporated comfort and flexibility; durability; lightness; ease of adjustment
during the initial fitting and trial
phases; a construction system compatible with the plastic prostheses techniques commonly in use; and a procedure that is adaptable and can accommodate further advances in materials
technology (i.e., vacuum forming, Spectra® fibers or other new materials)1.
Considerations
The primary objective of most lower extremity prostheses is to restore mobility. Obviously, levels of mobility differ,
ranging from the household ambulator
to the far-ranging athlete. To achieve
any of these functional levels, the prosthesis must first fit comfortably.
In addition, heat and perspiration
must be considered. There is a long residuum that - for reasons of leverage -
must be encased by the prosthetic socket. The leather-type prosthesis allows
transpiration. The plastic type allows little or none. If an insulating insert or air
chamber is added to the latter, the heat
trapping effect is significantly increased.
Therefore, the totally enclosing types of
prostheses are not optimum in a warm
climate or on a patient who perspires
heavily or has poor hygienic habits (13).
Cosmesis is also important. Not much
can be done about the poor similarity to
the contralateral limb afforded by the
bulbous--end Syme amputation. As a result, this factor must be considered before surgery. If cosmetic restoration is a
primary concern to the patient, the
Syme level may be ruled out (5,11).
Fabrication is the final consideration.
Traditionally the Syme prosthesis has
been made using complicated and
heavy-duty construction techniques. For
the socket, many layers of nylon, nyglass, glass stockinette, etc. are combined with other materials such as glass
roving, Kevlar2, carbon fiber, etc. These
are then impregnated with epoxy-, polyester-3 or acrylic-type resins. Frequently, the foot is given similar special treatment. As a result, the prosthesis often
weighs more than desired and is complicated to make.
There is good reason for this heavyduty approach. In clinical practice,
these prostheses can fracture due to the
high activity level of the Syme amputee
when compared to other amputees (see
Figure 2
) (14,15). As a result, prosthetists are concerned about the burden of
momentary forces upon the walls of the
Syme prosthesis and strengthen them
accordingly.
There is a dilemma here. On one
side, strength and durability are necessary and can add weight and bulk. On
the other hand, the patient wants and
often has a specific need for a minimal
prosthesis that is light and cosmetic.
The tubular Syme prostheses (no openings to cause weak areas) are considered the strongest. Unfortunately, the
cosmetic result is often less than desirable due to the bulk of the chambers
necessary to allow entry (12). When
made lightweight, these too can buckle
or fracture (8).
Description
In brief, the proposed prosthesis is a
flexible, lightweight medial-opening-type Syme with a standard foot that is
bolted and adhered to the socket. The
flexible structure's integrity and
strength are enhanced through the engineered use of carbon graphite fiber.
The major thrust has been twofold:
- To optimize fit and function
through the application of new materials
to achieve both strength and flexibility.
- To reduce time and energy required in fabrication through simplifying design.
Technical Procedure
Take a plaster impression in the customary fashion, paying close attention
to weightbearing design and any individual anomalies. At this time, stand
the patient in the solidified plaster
wrapping. Use spacers under the amputated limb to establish the correct
height. With the patient standing comfortably, place anterior and lateral
alignment lines on the exterior of the
plaster wrapping.
Once modification of the positive
model is completed, heat and form a
Pe-lite end pad.3 This pad should extend up to the "equator" of the Syme
bulb but not interfere with the distal
edge of the planned window opening.
Bevel the entire edge of the pad to provide a smooth transition on the inner
surface of the socket. Now make a
hemispherical spacer of Pe-lite designed to provide an adequate recess in
the distal interior of the socket for the
Kingsley Syme retaining nut.4 Plan the
location of this spacer to accommodate
the foot's alignment and placement
(see Figure 3
). Temporarily secure the
spacer to the Pe-lite pad and then secure the pad to the positive model. Apply a PVA bag over the model, with
end pad and spacer in place. Do not
include the metal Syme nut.
Apply the material layers:
- One 1/2-ounce Dacron with extra
pieces as needed
- Two nylon stockinettes with the
ends sewn (reduces bulk)
- A single layer of fiberglass
wrapped in the proximal four inches
and over the distal end
- Two strips of 3/16-inch Pe-lite 1 1/4
inches wide. Taper (skive) these
around their entire perimeters to a fine
edge. The anterior strip continues from
the proximal edge of the ball up to the
tibial tubercle. The anterior vertical
edge is kept approximately 1/4-inch
away from the planned medial opening. The posterior Pe-lite strip is the
same length as the anterior and starts at
the posterior proximal edge of the ball.
Warm these two lengths of Pe-lite and
form them to the contours of the model.
Flatten a layer of 2-inch-wide unidirectional carbon fiber tape on a piece of
paper.5 This carbon tape strip should be
continuous and long enough to encircle
the ball and incorporate the length of
both Pe-lite strips (see Figure 4
).
Glue the Pe-lite to the longitudinal
center of the graphite using spray adhesive. Fold the parallel edges of the
graphite over the upper surface of the
Pe-lite strip. This will form the "Ibeam" configuration that optimally
employs the enormous strength of the
carbon fibers (15,16). Leave the center
section of the graphite that will shroud
the ball at its full width. Adhere all of
these to the layers of nylon already on
the model and in the places previously
measured (see Figure 4
).
Add: two more layers of nylon stockinette with the ends sewn, another layer of fiberglass top and bottom as in
step three, one finishing nylon.
Using polyester resin mixed at 75
percent to 25 percent rigid to flexible
proportion, laminate the above. Be
sure to saturate all layers thoroughly.
In our five prostheses, this resulted in a
reasonably thin socket with good flexibility. It allowed torsion and yet was
strong enough to absorb shock and tensile/compression stresses (15). It may,
for some patients, be prudent to add
more carbon fiber layers or substitute
Kevlar stockinette for one or two layers of nylon. "The choice of materials
to be used for socket fabrication depends entirely upon the patient's demands and requirement" (16).
Locate, design and cut out a medial
window. Make a horizontal mark approximately '/8-inch above the "equator" of the bulb. Measure the circumference of the bulb. Wrap the measurement tape around the tibial shaft and
proceed proximally until the same measurement is noted and mark the socket.
At a level 1/2-inch proximal to the mark,
make a definitive horizontal line for the
proximal margin of the window.
Remember, the vertical tibial border
of the window is 1/4-inch away from the
edge of the carbon tape and parallel to
it. The width of the cutout is equal to
approximately one-fourth of the measured circumference of the bulb. If
there are doubts about the opening design, use a check socket. Mark the posterior vertical limits of the window on
the horizontal lines. With a straight
edge, connect these two points and
mark the anterior window border (9).
Look at the window thus designed to
make sure it is cosmetically correct.
Draw in radii at the four corners. These
should be sufficiently large to be cut in
one pass with an autopsy blade on a
cast cutter. It has not been necessary to
do a second lamination to finish the
medial window. Forethought, accurate
measurement and careful cutting of the
window from the socket have been sufficient to make a clean opening. Place
1/8-inch padding on the inner surface of
the window and close it with two one inch Velcro(r) straps.
Remove the plaster model from the
socket. Trim the socket and window,
and select the foot that is appropriate
to your patient's needs. We have successfully used several types of feet, including the SAFE foot, Kingsley Syme
SACH-both high heel & standard
height-as well as standard SACH
feet.6 Hollow out the keel section of
the foot to approximate the measured
height discrepancy of the patient.
Proceed with static alignment and
when satisfied with the location of the
foot, carefully mark it. Relocate the foot on the socket and mark the location for the attachment hole on the
socket. If unsure of the alignment, try a
test arrangement: Drill the smaller 3/8 inch hole and try the components on
the patient again using a 3/8-inch bolt
and thin standard nut to temporarily
hold it all together. Then drill the larger hole for the Kingsley heavy-duty
Syme nut. (The flange will rest on the
inside of the socket in the recess created for it.) When properly done, this
recess is slightly oversize in diameter
(see Figure 3
). Then, if foot adjustment
is needed, the through hole can easily
be enlarged to allow the nut to move in
its recess.
Anecdotally, one of our patients
wanted to be able to change back and
forth between low- and high-heel shoes
(boots). This was accomplished by
fashioning a mandrel on the distal
socket that fit into the Kingsley Syme
SACH foot. Since the recesses in these
feet are analogous, the mandrell maintains alignment. To exchange feet, he
had only to unscrew the foot bolt.
To achieve dynamic alignment, the
foot is bolted on with a piece of wet/dry
sanding screen between foot and socket. In this way, alignment changes can
be accomplished and maintained.
When the optimum alignment has been
achieved, mark the location and remove the sand screen. Bond the foot
and socket together with a strong acrylic adhesive such as Seiglehartz® and
replace the bolt.7 Be sure the socket
surface is roughened and that neither
surface is contaminated. Allow no
voids to occur in this adhesive. If the
foot-to-socket transition is less than
ideal, fill and smooth the margins with
a lightweight paste filler (e.g., 4110 & microspheres). Color this appropriately.
In our experience, the foot, attached
to by this method, can be removed and
replaced without destroying this socket.
Summary
We support the use of the Syme technique of amputation surgery when it is
medically appropriate. Both the physical and prosthetic advantages are significant and can considerably enhance
the quality of life for the amputee (16).
To further encourage use of the technique we have tried to simplify the fabrication (i.e., a single-lamination);
minimize the use of expensive materials; use standard resins and feet; eliminate extra steps (e.g., fabrication of
sleeves or inserts, multiple laminations, foot/ankle modifications, etc.);
make its components adjustable and
replaceable; and make it light yet
strong.
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