Computer-assisted surgery has been exclusively used whereas conventional surgery was only used for revision arthroplasty surgery. Thus more than 200 total knee prostheses were implanted with a system that may now seem outdated, but which, at that time, gave entire satisfaction from September 2003 to July 2006. The duration of the intervention and more specifically the time of tourniquet were studied [12] at the beginning and end of the user experience (Fig. 3) of this system. In July 2006, we decided to use a more user-friendly system including a touch screen covered with a sterile drape allowing us to avoid cumbersome cables and pedals. It is also 

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... reduced, limiting the aggression of the surrounding soft tissues (skin, subcutaneous cellular tissue, muscles and tendons). Some operators limit their incision to a few centimeters (approximately half a conventional incision). Clinical improvement was described in the immediate aftermath of these minimally invasive techniques. Studies are currently being carried out to confirm such progress. Computer-assisted surgery is the second line of research to improve the ancillary equipment. The computer appeared in operating rooms in the early 1990s under the leadership of neurosurgeons. The precursor surgical intervention was the computer-assisted transpedicular spine surgery, then, in the mid-1990s, it was followed by the computer- navigated total knee arthroplasty performed in France by the Grenoble university surgical team [10]. From the beginning, two systems were used, one using pre-operative imaging (CT), the other one using "bone-morphing" TM. At the time, the computer created practical difficulties because of its volume and the numerous cables required by a complex connection. An immediate preoperative tedious calibration of the ancillary equipment considerably lengthens operating time. For simplicity, concerning total knee arthroplasty, computer-assisted surgery must be regarded as a tool aiming to bring improved accuracy in the realization of bone cuts, leading to a better ligament balancing of the prosthetic knee and a global alignment of the lower limb being more frequently close to the vertical (the ideal range of the angle between the femoral mechanical axis and the tibial mechanical axis extending from 3 degrees of varus to 3 degrees of valgus). The so-called femoral mechanical axis is the line joining the center of the femoral head and the center of the knee; the tibial mechanical axis connects the middle of the tibial plateaus and the center of the ankle joint. Thanks to that regularity in the alignment, the unexplained outliers of the overall mechanical axis of the lower limb are scarce. With the help of a stereoscopic infrared camera, the rays being reflected by optically reflective balls, it is possible to obtain a virtual anatomical reconstruction of the operated knee. The software, using an extensive database, then guides the various bone cuts via a graphical user interface (screen) and benchmarks for instant viewing of the various cutting blocks. This is seen as an aid to surgery and not a robot automation of the surgical gesture. The surgeon remains the master of the surgical gesture, following on the screen the computer’s visual indications to guide and set the different cutting blocks. As mentioned above, this improvement in cutting accuracy induces a better ligament balancing and an alignment of the lower limb more consistently correct, which should increase prosthetic longevity. However no study has so far clinically demonstrated any lengthening of the lifespan of a so- called “navigated” total knee prosthesis. The follow-up is too short, which explains this gap. Indeed, computer navigation is still, in terms of its regular practice, in its infancy. Therefore the success is less massive than expected with the improvements achieved during surgery. Among the reasons for this limited development, the cost of materials [11] is mentioned, given its limited distribution. Longer operative time with the addition of specific technical steps required by the computer, leading to an increased septic risk, and finally difficulty of learning the technique, even for a trained operator. Given his experience and the excellent results of the so-called conventional prosthetic surgery, the operator is not always convinced that new technique is really useful. It seemed interesting to mention our personal experience of learning computer-assisted surgery in the field of total knee replacement. Indeed, the obstacles seemed to be overcome without great difficulty. Using more user friendly and easier systems, we were even able to modify our practice as our experience grew. A comparison of operating times enabled us to demonstrate the permanent aspect of learning by making our adaption to a totally new and unknown computer system easier and easier. In February 2003 we achieved our first computer-assisted total knee arthroplasty. Two implantations were performed during the same operating session in the Val de Sambre clinic in Maubeuge. At the time, concerning the primary knee arthroplasty, the author exclusively used the Natural Knee II TM sliding prosthesis (Zimmer, Warsaw, Indiana, USA). The provision on a trial basis of the Navitrack Navigation System TM (Orthosoft, Zimmer) allowed those first two projects. It is an imageless system requiring the calibration of computer tools (pointer, and cutting blocks) (Fig. 1) during the operation and not involving the bone morphing TM. It was actually a simplified bone morphing including deposition of "computer chips" on the screen allowing to adjust cutting thickness (Fig. 2). The graphical user interface not being interactive, the use of keyboards and pedals in the immediate vicinity or in direct contact with the operative field was a source of congestion and increased the risk of lack of asepsis. After those two trials which were considered conclusive, the decision to purchase the equipment was made and, from September 2003, all primary knee arthroplasties were performed by the author using that ...