Background Giant cell tumors (GCTs) most commonly occur around the knee.The most beneficial procedure for this disease has been extensive curettage with reconstruction.However,since many GCTs may compromise the subchondral bone,surgery can further jeopardize the articular cartilage and result in secondary osteoarthritis.In this study,we aimed to determine the factors associated with the development of degenerative arthritis and the effect of bone grafting on the prevention of secondary osteoarthritis.Methods We retrospectively analyzed 76 patients with GCT around the knee.The mean age at first diagnosis was 31.1 years.Surgical treatments included extensive curettage and cementation with or without bone grafting in the subchondral bone.Patient follow-up was a median duration of 35 months,ranging from 18 to 113 months.Results The local recurrence rate was 5.3％ (4/76).Secondary degenerative changes occurred in 30.3％ (23/76) of the patients.Less than 10 mm of the residual thickness of the remaining subchondral bone was correlated with secondary degenerative changes in 57 patients (P ＜0.001).Of these 57 patients,56.5％ (13/23) treated with bone cement reconstruction alone developed secondary degenerative changes; following bone grafting,the rate decreased to 29.4％(10/34),with a statistically significant difference (P=0.041).Conclusions GCT patients with less residual thickness of the subchondral bone are more likely to develop degenerative arthritis after curettage.Bone grafting in the subchondral bone area is recommended when the residual thickness of the subchondral bone is less than 10 mm.