A Rare Case of Monostotic Fibrous Dysplasia of the Femoral Neck With Pathological Fracture: A Case Report.

Fibrous dysplasia is a rare benign bone disorder characterized by the replacement of normal bone with fibroblastic and osteoblastic tissue. We present a case of monostotic fibrous dysplasia in a 25-year-old male patient. The case highlights the clinical presentation, radiographic features, and management approach for this condition. This report aims to contribute to the understanding of fibrous dysplasia and its management options. A 25-year-old male presented with a chief complaint of persistent left hip pain. The pain was described as a dull ache, associated with difficulty in weight-bearing activities. There was no history of trauma or constitutional symptoms. Physical examination revealed externally rotated left lower limb. Range of motion of the left hip could not be assessed due to pain, with no neurological deficits noted. Initial imaging included plain radiographs of the right femur, which demonstrated a radiolucent lesion with a ground-glass appearance and cortical thinning. Magnetic resonance imaging of both hip joints reveals an irregular T2 hyperintense and T1 hypointense lesion involving the left femoral neck; moreover, few tiny cystic spaces are seen within the lesion. Part of the lesion is extending into the superior-lateral aspect of the femoral head and surrounding bone marrow edema with minimal left hip joint effusion, features suggestive of a primary bony tumour. Plain computed tomography (CT) of the hip joint and pelvis was suggestive of an expansile lytic lesion with thin bony septation within and thick sclerotic margin in the left femoral head and greater trochanter associated with sub-capital femoral neck fracture suggestive of bone neoplasm (? giant cell tumour > simple bone cyst). A bone biopsy was performed, and histopathological examination confirmed the diagnosis of fibrous dysplasia, with characteristic woven bone and fibrous stroma. In this case, after confirming the diagnosis, the patient was managed with total hip arthroplasty on the left side. Monostotic fibrous dysplasia is a rare benign bone disorder that can present with various clinical manifestations. Timely diagnosis through a combination of clinical, radiographic, and histopathological assessments is crucial. Management should be tailored to the patient's symptoms.