ObjectiveTo investigate the causes of the complications and prevention strategy by analyzing occurrence of prosthesis-related complications after extensible semi-joint prosthesis replacement for lower limbs osteosarcoma in children. MethodsEleven children with lower limbs osteosarcoma underwent resection of tumor and replacement of the extensible semi-joint prosthesis between May 2006 and October 2012. There were 6 boys and 5 girls, with an average age of 9.3 years (range, 7-12 years). The lesions located at the distal femur in 6 cases, at the proximal femur in 2 cases, and at the proximal tibia in 3 cases. The disease duration was 2-8 months (mean, 3.6 months). According to the Enneking stage, 3 cases were rated as stage ⅡA and 8 cases as stage ⅡB. The pulmonary CT and ECT results showed no pulmonary metastasis or multi spots before operation. All patients received preoperative chemotherapy treatment for 4 times. ResultsPrimary healing of incision was obtained in 10 cases. Infection occurred in 1 case at 1 week after operation, and was cured after symptomatic treatment. Nine patients received postoperative chemotherapy for 12 times, 2 patients for 2 times and 4 times respectively. One case died of multiple metastasis; in 3 cases of pulmonary metastasis, 2 cases died and 1 case survived after resection of metastatic lesion. Eight survival cases received a follow-up of 25-89 months (mean, 42.5 months). Loosening and dislocation of the proximal femoral prosthesis occurred in 1 case, loosening and subsidence of the distal femoral prosthesis in 1 case, subluxation in 1 case, and retraction in 1 case. The incidence of prosthesis-related complications was 50%. Lengthening operation was performed on 3 cases for 1 time, and on 1 case for 2 times. And 4 cases did not undergo lengthening operation. According to Enneking function evaluation standard after malignant tumor limb-salvage surgery, the results were excellent in 1 case, good in 3, fair in 3, and poor in 1 at last follow-up with an excellent and good rate of 50%. ConclusionThe prosthesis-related complications include loosening and subsidence, dislocation, knee instability, and retraction after extensible semi-joint prosthesis replacement for lower limbs osteosarcoma. The prosthesis-related complications can be reduced by the improvement of prosthesis design and manufacture, and the use of intraoperative bone cement, artificial mesh, and postoperative restrictive brace.