BACKGROUND A retrospective cohort study was conducted to evaluate the outcomes of massive allograft arthrodesis in the management of high-grade osteosarcoma around the knee. METHODS The results of 19 patients with high-grade osteosarcoma around the knee, which was treated by wide resection and reconstruction using allograft arthrodesis, were evaluated for a mean length of 7.3 years (range, 3-13 years). The mean age at the time of surgery was 13.3 years (range, 6-27 years). According to the Musculoskeletal Tumor Society staging system, 17 patients were stage IIB and 2 were stage IIIB at presentation. Evaluations were based on the oncologic results, non-oncologic results and complications. Functional evaluation was performed with the Enneking functional evaluation form. RESULTS Four patients (21.1%) died of their disease; 3 (15.8%) are alive with disease; and 12 (63.2%) are free of disease. Four patients (21.1%) had local recurrence of their tumor at a mean of 23 months postoperatively (range, 9-44 months). The mean time to union of the metaphyseal junction was 24.7 weeks (range, 16-30 weeks) and the diaphyseal junction was 47 weeks (range, 24-78 weeks). The overall complication rate was 31.6%, including 2 (10.5%) infections, 3 (15.8%) allograft fractures, and 1 (5.3%) nonunion. Our mean final functional result was 65%. CONCLUSION Due to the high rate of complications in this study, we conclude that allograft arthrodesis should be left as a salvage or "back-up" reconstructive procedure after resection of osteosarcoma around the knee, unless there are special indications for this procedure. We found allograft fracture to be the most common complication.