A 25-year-old woman presents with a 4-month history of progressive right knee pain that worsens with activity. She reports no fever, weight loss, or night sweats. Physical examination reveals mild tenderness over the distal femur without a palpable soft-tissue mass. Plain radiographs show a geographic lytic lesion with internal trabeculation centered in the epiphysis of the distal femur, extending to the subchondral articular surface. The cortex is thinned but intact, with no periosteal reaction and no extension into surrounding soft tissue. The physeal plate is closed.
Which of the following is the most likely diagnosis?