Introduction. The knee joint is a result of a complex interaction of tissues, including bones, muscles, tendons, ligaments and cartilage. In a pathological situation the function of the knee has to be reestablished using a knee prothesis. The goals of total knee arthroplasty (TKA) are to eliminate pain and re-establish a stable and balanced knee. From 2001 to 2016, 812 639 primary TKA were performed in Italy. Although most cases are successful, patients complain about instable knee joint during daily activities. A key element concerns the balancing of the knee, in particular the ligament balancing, a procedure affecting mainly medial (MCL) and lateral (LCL) collateral ligaments.