RESUMEN
INTRODUCTION AND IMPORTANCE: Osteosarcomas are primary malignant bone tumors that are driven from bone-forming mesenchymal cells and account for nearly 20 % of primary bone tumors. CASE PRESENTATION: A 16-year-old female presented with chief complaint of pain and swelling on her right knee for 6 months with history of trauma. Her knee mobility and ROM was limited due to pain and the mass. Physical examination revealed a 15 × 22 cm mass on distal part of right femur with visible dilated veins. There was normal distal motor, sensory functions. Imaging revealed distal femur mass with mixed lytic and blastic features, wide transitional zone with hair and periosteal reaction; features suggestive of osteosarcoma that was confirmed by histopathological examinations as intramedullary osteosarcoma. She undergone surgical treatment consisting of surgical excision of the mass with safety margins and knee reconstruction by knee arthrodesis using femoral-nail and bone cement technique with excellent outcome. CLINICAL DISCUSSION: Osteosarcoma is best investigated through plain imaging, MRI and possible CT with histology being confirmatory. It is best approached with meticulous dissection to ensure clear margins or if necessary, amputation. Following resection, reconstruction can be done. In this specific case, the tumor was on the distal femur and the underlying knee was arthrodesed using cemented nail technique in which a cemented intramedullary nail was inserted with excellent clinical outcome. CONCLUSION: Surgical approach to osteosarcoma can be performed through limb salvage or amputation. Arthrodesis with cemented nail technique using an intramedullary nail can be performed in some patients with excellent clinical outcome.