Bone tumor near the articular cartilage is hard to remove sufficiently without damaging adjacent joint. The purpose of this study was to evaluate the feasibility of navigation-assisted surgery for saving joint in bone tumor resection or curettage. In this study, the investigators hypothesized that computer-assisted surgery is feasible method to get both enough margin and joint salvage. Each of them is important intermediate factor for either oncologic outcome or functional outcome respectively. The investigators designed this study to find what proportion of patients who underwent computer-assisted resection could get enough margins using some criteria obtained by overlapping preoperative and postoperative images. The investigators also evaluated whether computer-assisted surgery can be feasible for joint saving using some criteria including functional outcome.