Aneurysmal Bone Cyst Presenting as a Pathological Subtrochanteric Femur Fracture in an Adolescent: A Case Report

Introduction: Aneurysmal bone cyst is a locally aggressive as well as benign bony lesion most commonly seen in adolescents. Although it mostly involves the metaphysis of long bones, presents as a fracture which is pathological in the subtrochanteric region of the femur is rare. The subtrochanteric femur is a biomechanically demanding region of the lower limb, and the presence of an underlying cystic pathology can complicate fracture management. Management of subtrochanteric femur fractures due to aneurysmal bone cysts in adolescents is limited, as described in the literature. This case is a rare presentation and to denote an effective surgical treatment with anatomical reconstruction and stable fixation. Case Report: A 14-year-old male presented with pain and inability to bear weight on the left hip joint following trauma which was trivial. There was localized tenderness and restricted hip movement on clinical examination. X-rays demonstrated left sided subtrochanteric femur fracture along with an underlying expansile lytic lesion. Magnetic resonance imaging was done in order to assess the extent of the lesion and to help in further management. The patient underwent surgical management, which consisted of curettage of the lesion, fixation using a dynamic condylar screw with cancellous allogenic bone grafting. Confirmation with the diagnosis of aneurysmal bone cyst was also confirmed using histopathology. The post-operative course was uneventful, and follow-up showed union of the fracture with incorporation of the bone graft with gradual full weight bearing without pain. Conclusion: Subtrochanteric femur fractures, which are pathological due to aneurysmal bone cysts, are rare in adolescents and are challenging to manage. This case demonstrates that there are satisfactory results if the lesion is managed by clearance combined with bone grafting and stable internal fixation. The novelty of this report lies in documenting the successful fixation of this rare presentation using a dynamic condylar screw. The important learning point is that adherence to both biological as well as mechanical principles are necessary for optimal outcomes in involving the subtrochanteric femur, which are pathological in origin.