In case of malignant bone tumor, the sufficient preservation of joint anatomy should be required even with resection margin of 1.5 cm away from reactive zone of tumor. The sufficient preservation of joint is defined when at least 1 cm subchondral bone is remained after tumor resection, because 1 cm subchondral bone is required for fixation with allograft in subsequent reconstruction. The sufficient preservation of joint is also defined when articular surface is removed, but more than 50% of articular surface has to be saved.