ABSTRACT
The solitary osteochondroma or exostosis, is the most benign frequent tumor of the skeleton. It is the privilege of the young. It can be solitary or multiple in the framework of a multiple hereditary osteochondromata. The surgical indication is retained only when the tumour becomes symptomatic. The degeneration occurs in 1 to 25%, this rate increase when the great size tumors and the old patient. We report the case of a 25 years old patient, presenting a solitary osteochondroma of the left lower femoral metaphysis, with signs of malignancy in low grad secondary chondrosarcoma, suspected on elements of imagery and confirmed by the biopsy, this patient has underwent a monobloc large resection of the tumor, the bone and the adjacent muscle, with a favourable outcome after four years. This case illustrates the great limits ambiguity between the benign and the malign in the cartilaginous neoplastic pathology of the bone and the importance of the respect of algorithms of the skeleton tumors surgery in suspicious cases, because even if the histological examination of the operative model has not found the clear malignancy aspect, that does not eliminate the diagnosis of a chondrosarcoma, indeed, the histological distinction between an osteochondroma and a chondrosarcoma of low rank is very subtle