An Efficient Low Cost Prosthetic Structural System
Geraldo R. Angarami, C.P.
Carlos E. Samaria
For the lower extremity amputee, we have developed a prosthesis which we call Sauer-bruck Trimodular Physiological Prosthesis. The
prosthesis has been proven to be highly efficient due to its light weight and durability. It has a knee control mechanism that is easily
adjusted by the patient. The result is a highly versatile and inexpensive prosthesis, comparable in quality and features to other prostheses
of much higher cost.
Forty to 50 Sauerbruck prostheses are manufactured and sold per month. Case histories on file exceed 2,600 above-knee prostheses
and 2,000 below-knee. In Argentina there are a greater number of above-knee amputations than below-knee because many vascular
patients are treated too late, thus resulting in more severe amputations.
A total of 2,610 above-knee prostheses (Figure 1)
, weighing approximately four pounds each, have been manufactured. The prostheses
have a knee bolt length of 3", which provides improved durability due to the increased bearing surface. The bolt is assembled with teflon,
self-lubricated bushings, and the fastening nut has an inverted thread that self adjusts with use. The friction control mechanism (Figure 2)
is placed at the back under the bolt, where the friction adjustment is located. This mechanism is constructed of two metal bands: a steel
band to which the regulating nut is welded, and a bronze band against which the knee bolt bears. Bronze is placed against the steel bolt
because these materials are compatible and provide an efficiently regulated friction. This
mechanism is controlled by a screw which is adjusted with a wrench. The amount of friction is controlled by compression of a rubber
washer. The friction control assembly grasps the knee bolt during extension to limit terminal swing impact and, due to the decompression
of the rubber washer, loosens during flexion. The knee extension assist is located anteriorly with an elastic lower part going through the
knee and ending in an attachment to the proximal part of the socket. The assist contains many holes in the upper end so that the patient
may adjust the speed with which tbe knee extends. The knee allows maximum flexion without obstructions (Figure 3)
. The knee extension
stop has a large bearing surface cushioned by a long-lasting soft rubber bumper, which is easy to change in case of wear and does not make
any noise during extension.
The Sauerbruck knee may be used for residual limbs of all lengths without affecting the height of the knee center relative to the other
leg. The shin is trimodular in construction and made of seamless steel tubes. To adjust the length of the shin, the unit's telescopic tubes
are used. To finish, the device is welded in the correct height, providing a monostructure. This is considered to be the key to the unit's
success. Limbs in use for many years have continued to work without any kind of repair or maintenance.
The ankle has an alignment device made of two spheroidal discs, a concave one and convex one. A slot allows the discs to slide relative
to each other for the correction of the dorsiflexion and plantarflexion as needed. The top surface of the foot is hollowed with a cutter to conform to the contour of the discs in order to provide a proper seat. Consequently, the
weight of the prosthesis can be reduced by eliminating the weight of a seating base. The shin can be adapted to any type of foot, either SACH or articulated. There are alignment discs of similar
design that may be imposed between the socket and knee as an aid in alignment.
When the socket is made of wood, it may be fastened to the knee with special screws; when it is made of polyester, it is glued to the
knee with resin. Wooden sockets are used because their compatibility and adaptation to the human body is considered greater, especially
during heat waves, as wood absorbs perspiration. In finishing, the thigh is laminated and the intermediate cups, if used, are removed during
the transfer and finishing.
We have fit 825 manual locking knees called "ankerum," which lock themselves automatically with an internal elastic strap that pulls
the locking lever into position. The lever is attached to the proximal portion of the knee and in its locked position bears against a ledge on
the shin (Figure 4)
. This system may be used with long residual limbs without compromising the cosmesis of the prosthesis. It is important
to point out that the broad bearing surface of the locking lever guarantees reliable locking. To unlock the knee, the user pulls the strap. In cases where a pelvic belt is used, the strap is attached to the belt and the unlocking takes place automatically
when the patient sits (Figure 5)
. Thus, unlocking is achieved without manually pulling the strap.
A total of 2,090 Sauerbruck prostheses for below-knee amputees have been manufactured (Figure 6)
. This prosthesis consists of a tn-tubular, parallel structure, constructed with semispherical
and convex devices at the opposite ends of the tubes (Figure 7)
. It allows for bi-directional, multi-angular, and
rotational correction alignment. The whole structure is a geometrical bi-pyramidal unit with the bases aligned at right angles to each other, medial-lateral proximally and anteroposterior at the
foot, thus minimizing wear on the moving parts.
The parallel towers are made of 5/8" and 1/2" seamless steel tubes assembled together to allow height adjustment via telescopic movement. Once it is aligned and the final height of the prosthesis is determined, the tubes are welded together for strength and to provide a monostructure.
Using the same tubular pyramidal principle, 192 prostheses for hip disarticulation patients (Figure 8)
have been successfully fit. Both knee and hip joints are used. The axis of the hip is
placed at the anterior part of the socket, according to standard techniques, thus providing alignment stability. The hip joint is of similar characteristics as the knee
and contains the same constant friction control. The adjustment of the attitude of the socket relative to the thigh is achieved by trying rubber bumpers of different thicknesses between the
two at the joint. The thigh structure is telescopic for height adjustment and nothing obstructs complete flex- ion. An elastic strap, which proximally fastens posterior to the greater trocanter,
is used to extend the knee and to limit flexion of the hip.
The sockets are made of epoxy, thermoplastic, or metal and leather according to the
patients' wishes. They are finished in a highly aesthetic fashion and weigh no more than seven pounds.
Ortopedia Alemana has used this modular system, which has proven itself to be very practical for patients of all ages and lifestyles, for more than ten years.
Gerardo R. Angarami, C.P., is Director, Ortopedia Alemana, Montevideo 865, Buenos Aires, Argentina.
Carlos E. Samaria is President, Ortopedia Alemana, Montevideo 865, Buenos Aires, Argentina.
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