Hydatid Disease Masquerading as Infected Non-Union of Subtrochanteric Femur: A Rare Case Report.

Introduction: Infected non-union of the subtrochanteric femur is commonly attributed to bacterial infection and mechanical instability; however, rare etiologies may mimic this presentation and delay appropriate management. Hydatid disease involving bone is an uncommon manifestation and is often overlooked due to its non-specific clinical and radiological features. Reports of intraosseous hydatid cyst presenting as infected non-union are exceedingly rare, making this case clinically significant. Case Report: A 32-year-old female of Indian origin presented with pain, inability to bear weight, and a discharging sinus over the proximal thigh 9 months following fixation of a subtrochanteric femur fracture. Clinical and radiological findings were suggestive of an infected non-union. During surgical debridement, multiple cystic structures were encountered within the bone, raising suspicion of an unusual pathology. Further evaluation revealed hydatid disease involving the liver. The patient was managed with a staged approach including debridement, stabilization, antiparasitic therapy, and subsequent definitive reconstruction with total hip replacement. At follow-up, the patient showed good functional recovery without recurrence. Conclusion: This case highlights a rare presentation of hydatid disease mimicking infected non-union, emphasizing the importance of considering atypical etiologies in endemic regions. It adds to the limited orthopedic literature on osseous hydatidosis presenting as implant failure and underscores the role of intraoperative vigilance and multidisciplinary management. This report broadens the understanding of disease presentation and reinforces the need for tailored treatment strategies in complex non-unions.