Computer Navigated Hip Replacement
When performing hip replacement surgery the surgeon has to accurately place the new hip in a position that enables the new joint to function perfectly. If the position is not correct then, the hip can dislocate (the ball and socket separate, which usually requires an anaesthetic to put the hip back in joint); the leg can be a different length; the muscles may not function optimally and the joint can wear out earlier than expected.
The computer navigation system works by combining computers, infrared cameras and instruments that reflect infrared light back to the camera. The computer system creates an image of the hip joint during the operation, and it coordinates reference points on the natural hip to those on the new hip. This permits the surgeon to finely adjust the position of the new hip with certainty, so that he can orientate the replacement joint to function optimally with the bones, muscle, ligaments, and other structures around them. The surgeon is always in control of the operation and only uses the computer to provide information on where to place the new hip. When using the computer navigation, pins are required to be temporarily inserted into the bone; they are then removed once the new hip is inserted. This requires two very small (half a cm long) cuts to be made on the skin over the pelvis bone, which is in addition to the standard scar over the side of the hip that is used to insert the new hip.
Patients undergoing a Total Hip Replacement without computer navigation have a high incidence of a leg length discrepancy; (one leg being longer than the other) after their operation. This is due to the fact that the usual methods that a surgeon uses of checking leg length are notoriously inaccurate. The computer can avoid this by precisely measuring the leg length difference during the operation, which enables the surgeon to correct this.
The interest in the particles released by the metal bearings of certain hip replacements and hip resurfacing has focused attention on the importance of the correct placement of the hip joint in hip replacement and hip resurfacing. The computer navigation system provides the surgeon with detailed information on where the new hip is to be positioned, allowing the surgeon to place the hip in the correct position. This avoids problems with incorrect positioning, leading to the potential problems associated with the new joint wearing out. The computer also provides detailed information on how much the muscles have been stretched around the hip, to enable to surgeon to correctly position the new joint to provide the best function to the patient following the replacement.
The computer technology is still rapidly advancing, with the new systems generating a “virtual model” of the patients’ hip and then calculating what the optimum position the hip should be placed in to provide the individual patient with the very best result. This is due to the fact that different peoples’ hips are all slightly different and therefore a “one position fits all” approach does not provide the optimum solution. The computer is clever enough to do a huge number of calculations, once it knows certain information about the patients’ hip and provides the surgeon with the information required to place the hip in the perfect position for that patient.
Unfortunately, computer navigation in hip replacement is still not used by all surgeons despite the obvious advantages. In England and Wales only 1% of all hip replacements are performed with this technology. One of the main reasons why this technology is not more widespread; is that it can take longer to perform the surgery until the surgeon becomes skilled in using the information provided by the computer and the use of different instruments. However, this extra time is minimal once the surgeon becomes proficient and in Prof Davis’ practice he is able to perform the computer navigated hip replacement in approximately 45 minutes, which is quicker than some surgeons who perform hip replacement using the conventional technique.
