What is adequate blood flow? While uncompromised blood flow with zero pressure on the skin would be optimal, this does not sufficiently preload the soft tissue to provide the biomechanical advantages inherent in the CRS socket. Additionally, within any prosthetic interface where the skin meets an interface wall, zero pressure at the skin is simply not possible. At the other extreme, however, fully compromised or zero blood flow is obviously not an option. The answer lies somewhere between these two extremes.
A third approach is to use a laser-scanning tool to create an exact replica of the exterior of the soft tissue either loaded or unloaded. We have developed a casting jig system to increase precision during the casting process and will be working with computer-aided design systems and their manufacturers to develop the appropriate tools for digitizing and fabricating the high-fidelity interface. When this model is placed on a computer screen with suitable software, the socket can be modified that results in a good first check socket. Rules can be built into the software to modify sockets consistently from patient to patient. For instance, the overall shape can be reduced by a percentage to create a tighter interface. More importantly, the software can be set up to keep the area through any cross section at its initial value or at a value that is reduced by an exact percentage. Such a rule automatically generates the required release areas when the depressions are generated. Some work has been done on creating this software, but again, it is not yet ready. The prosthetist fabricating a TF CRS socket for the first time will benefit from using the casting jig to create the depressions in a traditional plaster wrap. The experience gained will be invaluable when suitable software becomes available.
DOUBLE WALL BELOW KNEE PROSTHESIS WITH REMOVABLE KNEE BRACE ..
The explicit addition of release areas allows the prosthetist to change the traditional double-wall socket into an open-frame interface. Typically, the load-bearing structures become stiff carbon fiber struts and brim structures, with the remaining tissue covered by only a thin flexible membrane that replaces the traditional hard inner socket. In some areas, even the membrane can be eliminated for enhanced cooling and suspension. The four longitudinal depressions in the latest design lock the radius and ulna along their entire length while the release areas between them receive the displaced soft tissue. Merely adding room for muscle hypertrophy as is commonly lauded as a design feature in many sockets is insufficient to stabilize the bones. The four depressions also prevent the rotational instability present in prior designs, allowing for a much lower proximal trim.
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When the humerus is amputated mid-length and is then placed in a typical tight cylindrical socket, considerable potential prosthetic motion is lost when the limb tries to move the socket. This lost motion occurs because the end of the humerus must compress the muscle and fat between the bone and the socket wall before force can be transmitted. In the same way, the proximal socket must compress tissue before substantial torque can be applied to move the prosthesis. Two problems with a conventional socket must be considered. First, the forces are mainly applied only near the end of the humerus and to the bone under the brim, and second, considerable motion is lost before the limb can move the socket and prosthesis. illustrates what happens when a load is applied between a conventional socket and the underlying tissue. Before the load is applied, the bone is centered in the socket. As a load is applied, the tissue must first be compressed until it reaches the level of compression to which no further motion is possible. In illustrations in , -, and -, the dashed line represents the level of compression to which no further motion is possible. shows how far the humerus must move before the prosthetic socket can support a substantial load.
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This article will introduce improved sockets for persons with TR, TH, and transfemoral (TF) amputations created with longitudinal depressions added in the socket walls with open release areas between the depressions that receive the displaced tissue. When the depressions and release areas are correctly located, they reduce motion of the underlying bony structures with respect to both the socket and the rest of the prosthesis. One can define the depressions and releases during cast-taking but only by radically changing the way casts are taken.