What condition is characterized by a unilateral limp and external rotation of the hip in an obese teen?

The condition characterized by a unilateral limp and external rotation of the hip in an obese teen is indeed slipped capital femoral epiphysis (SCFE). This condition occurs when the femoral head becomes displaced due to slippage at the growth plate, typically during periods of rapid growth, which is common in adolescents.

The presentation of a limp, particularly when it is unilateral, and external rotation of the hip is classic for SCFE. In this condition, the affected leg often appears shortened and may be held in a position of external rotation. This abnormal positioning is due to the instability at the growth plate, leading the hip joint to function improperly.

SCFE is more frequently seen in overweight and obese adolescents, which aligns with the characteristics mentioned in the question. Early diagnosis and management are crucial to prevent further complications, such as avascular necrosis of the femoral head.