In orthopaedic surgery, with a special focus on Total Knee Arthroplasty (TKA), planning the intervention is of fundamental importance. The rate of success of the surgery is strictly connected to the right alignment of the prosthesis. In order to improve overall alignment and to minimize situations of gross positioning, systems for computer-assisted total knee arthroplasty have been introduced. These systems use computer technology for surgical planning, for guiding or performing surgical interventions. The surgeons use computer-assisted systems to acquire the surface of the bone, then the software reconstructs the patient-specific morphology and plans the most appropriate cut, depending on the characteristic of the intervention and on the surgeon’s specifications.