COMPUTER-ASSISTED KNEE TOTAL ARTHROPLASTY

1 PhD, Orthopaedics and Traumatology Institute, Hospital das Clínicas, Medical College, University of São Paulo. 2 Assistant Doctor, Orthopaedics and Traumatology Institute, Hospital das Clínicas, Medical College, University of São Paulo. 3 Emeritus Professor, Department of Orthopaedics and Traumatology, Medical College, University of São Paulo. 4 Post-graduation student, Orthopaedics and Traumatology Institute, Hospital das Clínicas, Medical College, University of São Paulo. INTRODUCTION Technological evolution has marked the recent history of medicine, revolutionizing diagnostic and therapeutic methods in all its fields. In this context, one of the most recent achievements is the computer-aided orthopaedic surgery (CAOS). The development and clinical application of computer-assisted surgery systems in orthopaedics has recently resulted in the establishment of a specific international society, the CAOS International, the first meeting of which occurred in 2001, in Davos, Switzerland. In our environment, we got the first computed-assisted orthopaedic surgery system in 1999, at the Orthopaedics and Traumatology Institute, Hospital das Clínicas, University of São Paulo, which was donated by Aesculap Academy. That system, named OrthoPilot, is intended to Surgical Navigation in Orthopaedics, its major application is on Knee Total Arthroplasty, with which we had our first experience in this area. OrthoPilot was the first navigation system for knee arthroplasty to be widely employed in clinics, especially in Europe. Navigation consists of surgical instrumentation guidance, offering objective intra-operative parameters to surgeons, providing accuracy and safety to a surgical procedure, enabling the performance of minimally invasive procedures, and reducing or mitigating exposure to X-ray. Thus, navigation is the surgical or intra-operative arm of CAOS, which can also be applied in surgical planning, results simulation, and robotics. Many reference possibilities exist for navigation systems, those based on images that can be captured before or during surgical procedure (computed tomography (CT), magnetic resonance (MR), fluoroscopy, ultra-sound (US), etc) and those that are not based on images, but in anatomical references captured during surgical procedure. OrthoPilot fits in the latter group, with particular anatomical points of a patient are sent to the computer during surgery through infrared (IR) active conveyors, which are found by an optical tracking system similar to a GPS (Figure 1). The position and movement of those points are followed up in real time by the computer, allowing to find the core of the three major joints of a patient’s lower limb by a mathematic algorithm applied to the performance of standardized movements of those joints, thus enabling a virtual reconstruction of the lower limb’s mechanical axis. The association of this lower limb virtual model to anatomical references achieved ant to the presence of IR conveyors (Figure 2) in tibial and femoral section guides enable bone sections to be performed in a surgical procedure to be guided by the computer in an accuracy degree equal or lower than 1o. The system “sees” the section guides and their position towards tibial and femoral joint surface and to lower limb’s mechanical axis, providing a feedback to the surgeon by means of a virtual image on screen with objective parameters about the result to be achieved as a result of section guides position, namely: section thickness and angle towards mechanical axis at frontal and sagittal planes (Figure 3). Therefore, conventional alignment guides are not used, with intraor extra-medullar reference, thus reducing the risk of thromboembolic complications as well. Here, we report the results of lower limbs alignment for our first series of 72 knees in 68 patients submitted SUMMARY One of the most significant technological advancements in current medicine is the computer-assisted surgery, which, for orthopaedics, one of the major uses of this technology is in knee arthroplasty. The main contribution provided by computer-assisted orthopaedic surgery (CAOS) to knee arthroplasty is its potential to improve prosthesis implant precision and the operated limb alignment, contributing to results optimization and longevity. The image-independent navigation, based on anatomical references acquired during surgical procedure through infrared rays’ transmitters, has been the prevailing technique in knee arthroplasty. We used the navigation system “OrthoPilot” version 2.2 in total knee arthroplasty for inserting ORIGINAL ARTICLE