Computer Assisted Joint Replacement
As the name suggests it is computer-assisted surgery, the computer assists the surgeon, but the actual surgery, is done by the surgeon.
Basically there are arrays, which are fixed to the bones (fig 1), which emit/ transmit the infrared signals, which are picked up by an infrared camera. There are also instruments, which emit/transmit the infrared signals which are picked up by the infrared camera (fig -1). These instruments are used to register the important landmarks inside the joint. The infrared camera transmits these signals to the computer. The computer then processes these signals and accurately generates very important parameters such as the weight bearing mechanical axis, the joint line ,and also parameters which helps in gap balancing(video-1).
The weight bearing mechanical axis is a very important parameter on which the long-term survival of the artificial joint depends upon. This can be compared to the vehicle wheel alignment, which is done before the tires are changed (fig-2). If the wheels were not aligned optimally the tires would not last long. Similarly the weight-bearing mechanical axis of the lower limb is deranged when it is affected with osteoarthritis of the knee joint (fig-3). This has to be rectified to optimal levels before an artificial joint is put in, if not the artificial joints would not last long. The computer assistive technology helps in accurately guiding the surgeon as to where the mechanical axis is.
Whatever technology is used, principally one has to make sure that the weight-bearing mechanical axis of the lower limb is realigned (fig-4) before an artificial joint is put in, there are evidences which emphasizes that this weight-bearing axis has to be corrected to optimal levels to get maximum mileage out of the artificial joints. The artificial joints have interfaces such as metal, cement interface and cement, bone interface that does not tolerate uneven loading and would result in early failure.
There are various techniques of performing a total joint replacement, such as the mechanical jig-based, computer assisted, patient specific jigs, and robotic arm assisted total joint replacement. Whichever method the surgeon uses, principally one has to make sure that the mechanical weight-bearing axis is realigned to an optimal level, so that the artificial joint implanted would last long. There are evidences to show that by using computer assisted joint replacements this important parameter is realigned very accurately.
