[Paraosteal osteosarcoma of the tibia treated with the OSS prosthesis. Case report].

Parosteal osteosarcoma originates on the surface of long bones and spares the medullary canal. Its peak incidence occurs in the third decade of life and it is more frequent in females than males. The juxtacortical variety of parosteal osteosarcoma is one of the most common ones, accounting for 1-6% of all osteosarcomas. The classical radiographic appearance of osteosarcoma includes high ossification density and a lobed mass, usually in the posterior aspect of the distal femur, sparing the medullary canal. We report herein the case of a 31 year-old male patient with a clinical picture that included left knee pain and who was seen as outpatient. He was started on treatment for enbloc resection of the tumor and implantation of the OSS (Orthopedic Salvage System) prosthesis. Treatment consisted of broad resection of the proximal tibia, of approximately 14 cm, as well as the implantation of a nonconventional modular tibial prosthesis. Both the radiographic and the clinical results were good and appropriate at the three week follow up.