Limb Salvage Using Knee Arthrodesis Endoprosthesis for Ewing Sarcoma With Extensor Mechanism Loss: A Case Report and Surgical Decision-Making Review.

Introduction: Malignant tumors around the knee pose a complex reconstructive challenge, particularly in the setting of an unreconstructable extensor mechanism. Although limb-salvage surgery with megaprosthetic reconstruction is the standard approach, its success is contingent upon extensor mechanism preservation. When this is not achievable, knee arthrodesis with modular endoprosthetic systems remains a robust salvage strategy. Case Presentation: A 17-year-old male presented with a one-year history of progressive left knee swelling, pain, and functional impairment. Imaging demonstrated extensive involvement of the soft tissues, distal femur, and proximal tibia, with articular extension and close association with the patellar tendon. Biopsy confirmed Ewing sarcoma. The patient underwent neoadjuvant chemotherapy with vincristine, doxorubicin, and cyclophosphamide. This was followed by wide oncologic resection, including the distal femur, proximal tibia, and extensor mechanism, and reconstruction with a knee arthrodesis prosthesis. Final histopathology confirmed negative margins and 30% tumor necrosis. At 6-month follow-up, the patient remained disease-free with satisfactory functional recovery. Conclusion: Endoprosthetic knee arthrodesis provides a durable and oncologically sound limb-salvage option in cases where the extensor mechanism cannot be reconstructed. Optimal outcomes depend on appropriate patient selection and rigorous oncologic management.