Total knee arthroplasty (TKA) is one of the most clinically successful and cost-effective interventions in health care, with numerous investigators reporting excellent long-term results in terms of reducing pain, improving function, and increasing quality of life in patients. Among the many factors that influence TKA outcomes, surgical technique and final prosthesis alignment appear the most critical. It is known that an accurate restoration of the overall lower limb alignment reduces polyethylene wear and therefore the risk of aseptic loosening. Furthermore, errors in varus/valgus alignment greater than 3 degrees for the femoral or tibial component have been shown to result in less satisfactory clinical outcomes and a higher risk of loosening. Also, malrotation in the transverse plane of the femoral or tibial components has been shown to affect correct function of the extensor mechanism of the replaced knee, which may lead to anterior knee pain. The elevation of the joint line limits the range of motion of the knee. Finally, instability, malalignment, and/or malposition are the major reasons for TKA revision and, except for infection, are all related to incorrect surgical technique. Although various guides for alignment have been designed to improve accuracy, several limitations remain.
Computer Assisted Orthopedic Surgery (CAOS) is a discipline where computer technology is applied pre-, intra- and/or post-operatively to improve the outcome of orthopedic surgical procedures. The principal idea behind CAOS is that operative outcomes will be improved through the use of computer technology. Taking the example of joint replacement, the task of the surgeon is to integrate the new joint components into the patient's existing anatomy. CAOS technologies allow the surgeon to: plan the component placement in advance, including determination of the appropriate component sizes; measure the intra-operative placement of the components in real time, making sure that the plan is adhered to; and measure the post-operative result.