Monostotic fibrous dysplasia in the proximal tibial epiphysis: a case report

INTRODUCTION Fibrous dysplasia is one of many well-known disorders in which there is a defect in the remodeling process of immature bone to mature into lamellar bone, and it often exists in metaphyseal and diaphyseal parts of the long bone. In this report, we describe a rare case where fibrous dysplasia was found only in the proximal part of the epiphysis of the tibia without other bony lesions. CASE PRESENTATION A 14-year-old Asian girl was referred to our hospital after slipping down with pain on the left knee. A radiograph showed an abnormal finding of a central radiolucent lesion with a marginal sclerotic border near the proximal tibial spine. A magnetic resonance image showed the lesion at low signal intensity on a T1-weighted image and at high signal intensity on a T2-weighted image. The biopsy results led us to conclude that the lesion was a fibrous dysplasia. CONCLUSION If an abnormal lesion on the epiphysis, especially in long bones, is detected on a radiograph, several differential diagnoses can be made. Although fibrous dysplasia is usually not encountered as an epiphyseal lesion, it is important to incorporate all the clinical, radiographic and pathologic features to diagnose monostotic fibrous dysplasia when the lesion is located at the epiphyseal location.