Osteosarcoma is the most common bone tumor that occurs in children and young adults with prevalence of teenage. There can be identified many subtypes of osteosarcoma by how they look on X-rays and under the microscope. Osteosarcoma can be classified as high-grade, intermediate grade, or low-grade. This has a significant prognostic value of tumor development suggesting the growth rate and the potential for expansion. Between 2009-2013, in the Department of Orthopedics and Traumatology, University Emergency Hospital of Bucharest, Romania, were treated seven cases of osteosarcoma of the proximal third of the tibia in young, early-diagnosed cases without metastasis. The treatment involved resection of tumor formation and reconstruction with a modular prosthesis. Postoperative patients were mobilized for a week without charging the operated limb under the protection of orthesis. During this period continued active and passive mobilization of the ankle and foot to prevent stiffness and to reduce postoperative swelling. From the second postoperative week, patients are mobilizing with progressive charging but not being allowed to do any flexion in order to protect de insertion of medial gastrocnemius muscle rotation flap used to cover the prosthesis and to protect the patellar tendon reinsertion. This extensive surgery does not improve survival rate of these patients compared to treatment by amputation of this pathology but greatly increases the comfort of life and in all cases ensure socio-professional reintegration of these patients. To ensure optimal postoperative results perform a complete diagnosis and preoperative oncological treatment before surgery, if applicable.