**Core Concept**
Perthe's disease is a childhood hip disorder characterized by avascular necrosis of the femoral head. It occurs in children between 4 and 12 years of age, with a peak incidence around 5 years. The exact cause remains unknown, but it is thought to be related to a disruption in the blood supply to the femoral head.

**Why the Correct Answer is Right**
Perthe's disease is the most common cause of limp in children aged 5-9 years. The disease typically presents with a painless limp, which may progress to a painful limp. The pain is usually localized to the hip and groin area. As the disease progresses, the affected child may exhibit signs of limited hip movement and a characteristic "gait" or walking pattern. The disease is often bilateral, but it usually affects one side first.

**Why Each Wrong Option is Incorrect**
**Option A:** Tuberculosis (TB) of the hip is a rare cause of limp in children. TB hip typically presents with a more chronic history of pain, weight loss, and fever, and is often associated with a positive Mantoux test.

**Option B:** Congenital dislocation of the hip (C.D.H) is a rare condition that usually presents in the neonatal period or early infancy. It does not typically cause a limp in a child of seven years.

**Option D:** Slipped upper femoral epiphysis (S.U.F.E) is a condition that affects adolescents, typically around the age of 12-14 years. It presents with a sudden onset of pain and a limp, but is much less common in children aged 7 years.

**Clinical Pearl / High-Yield Fact**
Perthe's disease is often associated with a history of trauma or minor injury to the hip area. However, it is essential to note that most cases of Perthe's disease occur without any identifiable trauma.

**✓ Correct Answer: C. Perthe's disease**