Hydatid cyst is a condition endemic to many parts of the world and is mainly caused by Echinococcus granulosus ( E. granulosus). It rarely affects the bone tissue, with the most commonly impacted sites being the vertebrae and the pelvis. Preoperative diagnosis is challenging and very rarely possible because of its similarities with other pathologies. In this report, we present the case of a 64-year-old patient with osseous hydatidosis of a pathological distal femur fracture. The fracture pattern was not recognized on the initial operation and multiple serial debridements were required to control the disease, leading to a large bone defect and a weakened extensor mechanism. A knee arthrodesis with a segmental defect-bridging intramedullary system was eventually performed, which led to satisfying outcomes. Osseous hydatidosis very often presents itself as a pathological fracture and is difficult to diagnose preoperatively with plain radiographs. Orthopedic surgeons are advised to maintain a high index of suspicion and to test for this disease when cystic bone lesions are detected at fracture sites, especially in patients from endemic regions.