The restoration of the joint line (JL) is essential for the proper functioning of Total Knee Arthroplasty (TKA). The exact position of JL can be determined using anatomical landmarks such as femoral condylar width (TEW), tibial tubercle, fibular head, and adductor tubercle during preoperative planning or intraoperatively. However, in cases of severe varus deformity in Type M gonarthrosis, it is unknown which method is most suitable for accurately determining the precise JL position. The aim of this study is to identify the most appropriate method for determining the JL position in Type M gonarthrosis. To achieve this goal, two groups of patients with Type 1A and Type M gonarthrosis will be compared by measuring preoperative values and comparing them with intraoperative reference values.