Dysplasia epiphysealis hemimelic in the knee: a case report.

Background: Dysplasia epiphysealis hemimelica (DEH) is a rare congenital bone dysplasia characterized by overgrowth of the epiphyseal cartilage on one side, with its etiology remaining unclear. The condition predominantly affects weight-bearing joints of the lower limbs, typically presenting with localized pain due to a rapidly growing mass around the joint. In severe cases, symptoms such as limb length discrepancy and limb deformity may occur. Early diagnosis is challenging, and delayed diagnosis and treatment can easily lead to limb deformity and functional impairment. Case presentation: This paper reports the case of a 9-year-old male patient who was initially misdiagnosed with osteochondritis dissecans of the medial femoral condyle at a community hospital. After two months of immobilization and rest without improvement in pain, he was referred to our hospital, where the diagnosis was revised to DEH. We performed an open surgical excision of the lesion, and postoperative histopathological examination confirmed DEH. At 3-month follow-up, the patient had resumed normal walking. At 6-month follow-up showed complete resolution of pain and restoration of normal knee joint range of motion. At 2-year follow-up, there were no signs of recurrence, and knee function had recovered well. Conclusion: DEH is a rare condition that is prone to misdiagnosis. Establishing a correct diagnosis early requires a combination of clinical presentation, imaging studies and histopathological findings. This case suggests that DEH should be considered in pediatric knee lesions mimicking osteochondritis dissecans, and that complete excision can achieve good outcomes in selected patients.