To investigate the role of prosthetic arthroplasty in treating osteosarcoma around the knee joint and the related questions.Methods:Between 1993.9 and 2005.9,36 limb sparing procedures were done using mega prostheses after resection of osteosarcomas around knees,25 located on the distal femur and 11 on the proximal tibia,24 male and 12 female,the mean age when they receive the operations is 23.114-7.7 years(range,15~44 years),the mean time of follow up was 49.82 months (range,6~ 122 months).Limb function and life quality of the patients after operation are evaluated by 2 systems,MSTS (Musculoskeletal Tumor Society) and TESS (Toronto Extremity Salvage Score).