A 14-year-old boy is seen by his physician because of pain in the right hip. He is noted to have a limp on walking. His symptoms gradually developed over the past 3 months. The most likely cause of his symptoms is which of the following?

It is important to recognize this entity on x-ray. Treatment must be carried out to avoid further slipping of the joint epiphysis, because arthritis may result in neglected cases. Unlike fractures of the head of the femur occurring in older persons, the condition is unlikely to lead to necrosis of the femoral head.