In the operating room, one tiny millimetre can make the difference between illness and health, mobility and paralysis, success and failure. The orthopaedic surgeons at the University Hospital of Antwerp (UZA) have been the first in Belgium to introduce computer assisted surgery to facilitate their precision work. Within the UZA, the advanced CAS procedures are already frequently being applied for bone, head and neck surgery. The Müller Institute at the University of Bern in Switzerland has developed the CAOS or Computer Assisted Orthopaedic Surgery system that has been implemented in the Antwerp University Hospital to the tremendous delight of the Flemish surgeons who immediately have discovered the great potential and accuracy of the CAOS system.
Spinal fractures or lateral distortions can be treated with surgery by attaching screws to the spine. This is a rather delicate operation because vital nerves might be damaged, which can cause paralysis. Use of traditional procedures in 20 to 25% of the cases leads to inaccurate fixing of the screws. The physician has to rely on his intuition with regard to the exact location of tissue and bone structures. Since the arrival of the innovative CAOS system in 1997, the UZA surgeons have succeeded in reducing the percentage of ill-fixed screws to 2%, a truly remarkable improvement. A 3D patient image of the spine helps the doctor to determine the exact spot where the screw has to penetrate the vertebra, before actually fixing it. Before as well as during the intervention, surgical actions can be simulated and evaluated previous to the carrying out of any decision.
In December 1998, the UZA orthopaedists began to use the CAOS system for hip prosthesis implants as well. It is of extreme importance to properly align the acetabular cup in which the implant's femoral neck or ball joint will have to rotate, with the specific pelvis anatomy of the patient. The better the cup is positioned, the less the degree of wear debris resulting from impingement, and the smaller the risk for dislocation. In the near future, the Müller Institute will provide the UZA with software modules for knee surgery. First, a series of Computed Tomography (CT) scans of the lesion are taken. In case of a spinal fracture, the scanner produces different cross sections of the area in the spinal column. These slices are computed into a 3D reconstruction of the vertebrae. The thinner the slices, the more reliable the image.
The surgeon is able to explore the virtual spinal column from different angles to determine the ideal pathway for insertion of the screws and perform a pre-operative simulation on the computer. The pre-operative plan has to prevent complications from emerging afterwards. During the intervention, the doctor not only views the patient's virtual column and the pre-planned trajectory on the computer screen but also the exact position of the surgical instruments. Each instrument has been equipped with four light emitting diodes (LEDs) in order to permit the set of three infra-red cameras in the operating theatre to track the LED-signals. In addition, the computer has to locate the position of the real patient's column by coupling the virtual body part to it by means of four to six anatomic landmarks in the pre-operative CT image scans.
During the operation, one of the surgical tools, provided with LEDs, indicates the same landmarks in the patient's body. In this way, the computer is able to register the exact position of the real column. Dr. Dirk Vandevelde, who is the driving force behind the computer assisted orthopaedic surgery at UZA, stresses the importance of an accurate matching between the virtual and the real body part. The computer uses a quality index to express the exact value of the mutual matching. The surgeon is able to read it from the screen at any moment. The maximum deviation for one vertebra can be 0.5 millimetre but for another one, 1 to 2 millimetres. A solid reference base is being installed near the concerned body part, as not to disturb the matching by shifting the patient's or the camera unit's position while the operation continues.
The position of the anatomic landmarks and the surgical tools is compared to this base, registered by the computer through the four LEDs. For safety reasons, the computer has to take care that no steps are being missed and that each action takes place in the right order during the intervention. The use of computer assisted surgery is expensive. The basic equipment costs about 250.000 euro while each software module amounts to some 50.000 to 62.500 euro. As long as the social security system doesn't reimburse the patient, the UZA staff considers the expenses as an investment in innovative technologies. In the long run, computer assisted surgery is bound to save money by reducing the risk for complications, and avoiding difficult revision operations as a result.
By the end of 1999, the UZA orthopaedists will be able to ensure a perfect matching between the body part which has to be operated and its digital image. This will be achieved by way of ultrasound. A number of operations will become far less invasive with the support of computer assisted surgery. You can read more about these novel techniques in the VMW articles Virtual pelvis and hips sockets show surgeons where to screw and Surgeons align hips more accurately with HipNav which both appeared in the August 1998 issue.