## **Core Concept**
Perthes disease, also known as Legg-Calvé-Perthes disease, is a condition that affects the hip joint in children. It is characterized by the temporary loss of blood supply to the hip, leading to necrosis of the femoral head. This condition primarily affects a specific pediatric age group.

## **Why the Correct Answer is Right**
The correct answer, **B. 4-10 years**, is right because Perthes disease most commonly affects children between the ages of 4 and 10 years. This age range is crucial for the diagnosis, as the disease tends to manifest during this period due to the specific changes and vulnerabilities in the femoral head's blood supply during childhood.

## **Why Each Wrong Option is Incorrect**
- **Option A: 1-3 years** - This age range is too early for the typical presentation of Perthes disease. While it's not unheard of for younger children to be affected, it's less common.
- **Option C: 10-15 years** - This age range is generally considered too late for the typical presentation of Perthes disease. As children approach adolescence, the likelihood of Perthes decreases, and other hip pathologies become more common.
- **Option D: 15-20 years** - This age range is well beyond the typical age for Perthes disease. At this stage, other conditions such as slipped capital femoral epiphysis (SCFE) or hip osteoarthritis are more likely.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that Perthes disease has a higher incidence in males than females, with a male-to-female ratio of approximately 4:1. Additionally, it more commonly affects the right hip than the left. Early diagnosis and treatment can significantly improve outcomes.

## **Correct Answer: B. 4-10 years**