PROBLEM TO BE SOLVED: To provide a surgical instrument suitable for performing joint replacement.SOLUTION: A pelvis attachment 100 is placed on the patient's pelvis BA from above the skin, the femur head center is recognized based on it and a cutting drill positioning of the distal end of a femur is done by a femur distal end attachment. A foot joint attachment is placed on the patient's foot joint from above the skin, and a cutting drill positioning of the upper end of a tibia is done by a tibia upper end attachment based on it too. Thus, a mechanical axis passes through the femur head center, the knee joint center and the foot joint center, enables the bone to be cut at an angle reflected by the curvature/extension angle in the sagittal plane and the rotation angle in a cross section in a surgery plan during a surgery and the artificial knee joint replacement can be performed successfully.
