An afebrile, obese 14-year-old boy has developed pain at the right knee and a limp. Select the most likely diagnosis

Slipped capital femoral epiphysis is a disease of unknown etiology and occurs typically in adolescents; the disorder is most common among obese boys with delayed skeletal maturation or in thin, tall adolescents having recently enjoyed a growth spurt. Onset of this disorder is frequently gradual; pain referred to the knee in 20% of cases can mask the hip pathology.