In a case report the authors describe the course of the disease and therapy in a 14-year boy, who was diagnosed osteosarcoma of the right distal femur. Histological examination confirmed the clinical diagnosis of osteosarcoma. In spite of the considerable size, but in line with a good tumor demarcation a recommended surgical intervention saved the extremity by substituting the tumor with endoprosthesis. The surgery was made after preceding neoadjuvant chemotherapy and adjuvant chemotherapy continued after the operation. After a pertinent rehabilitation the patient was beginning to participate in common life activities. However, 11 months after a complete substitution of the knee joint and distal part of femur he accidentally fell down and the shaft of the tumorous endoprosthesis was bended and later broke at the border of polyethylene and bone tissue. This complication was solved 5.5 months after the bending by reimplanting a new, larger tumorous endoprosthesis. No signs of relapsing tumor were visible locally during the re-operation. The patient continued in the rehabilitation. He was satisfied with the results of the operation and re-operation. At the present time, 14 months after the re-operation, the patient is able to walk with the support of “French” crutch and is able to put a full load upon the lower extremity. In regular control examinations there were no signs of relapse or dissemination of the tumor process.

        Key words: osteosarcoma, surgical treatment, complications