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Computer-Assisted Surgical Navigation

Computer-assisted surgical navigation of the knee is a new technique used to optimize accuracy. Although computer-assisted joint replacement is identical to the traditional knee replacement, in many ways, exposure and time are fundamentally different. Computer systems are designed with a variety of different applications and qualities. Many of them rely on infrared tracking, which like a GPS, calculates elapsed time for signals to go and come between an infrared sender. By an extremely accurate mathematical calculation, angular distances can be precisely calculated.

Computer Assisted Surgical Navigation

Most computer-assisted navigation involves fixing frames around the knee by affixing them to the lower femur (above the knee) and upper tibia (below the knee). These reference frames are applied to the bone by small pins. Older CAOS systems use an infrared, stereostopic camera that follows the movements of these reference frames lets the surgeon know exactly where the femur and tibia are during surgery. Knowing where the positions of the surgical instruments compared to the bones during surgery allows the system to make an accurate calculation as well as predictions about all important aspects of the knee replacement surgery, including size, position, alignment, motion, and ligament balance.

CAOS (computer-assisted orientation surgery) also provides numerous advantages. For example, by avoiding the use of alignment bars and rods used to calculate positions of the traditional knee replacement systems, computer-assisted surgical navigation allows for the replacement to be performed without drilling holes in the end of the leg bone or femur, and pushing a metal rod into the femur to gauge alignment. This was the older method of performing a total knee replacement surgery. Many of the complications from knee replacement surgery are an indirect result of this particular maneuver in that they increase the bone pressure producing microembolism of the bone marrow, forcing air and/or fat during the knee replacement surgery into the circulatory system. Microembolism is often a subtle problem that can cause temporary confusion, mild breathing trouble, and occasionally respiratory distress following surgery. If these symptoms can be eliminated or at least reduced by the use of the CAOS system, while not sacrificing any type of accuracy, it is thought that this will lessen some of these postoperative complications.

A newer and more exciting variety of this is electromagnetic tracking systems. This has a distinct advantage in that it can look around a corner or through non-metallic objects. In a surgical application, this has definite advantages. Although still under development, this less invasive system gives us an idea of what horizons are still uncharted in terms of making more accurate the orientations of surgical navigation.

David R. Lionberger, MD, 2005