**Core Concept**
Perthe's disease, also known as Legg-Calve-Perthes disease, is a childhood hip disorder characterized by avascular necrosis of the femoral head. This condition results from a disruption in the blood supply to the femoral head, leading to ischemic damage and potential collapse of the bone.

**Why the Correct Answer is Right**
In Perthe's disease, the blood supply to the femoral head is compromised due to a disruption in the ligamentum teres or the medial circumflex femoral artery. This results in ischemia of the femoral head, leading to necrosis and potentially, deformity of the joint. The movement that is most affected in Perthe's disease is abduction, as the femoral head is no longer able to articulate properly with the acetabulum. This leads to pain and limited mobility, particularly in the abducted position.

**Why Each Wrong Option is Incorrect**
**Option A:** Flexion is not typically restricted in Perthe's disease, as the disease primarily affects the femoral head and not the hip joint's flexion mechanism.

**Option B:** Extension is also not significantly affected in Perthe's disease, as the femoral head's deformity does not directly impact the hip's extension mechanism.

**Option C:** Internal rotation is not typically restricted in Perthe's disease, as the disease primarily affects the femoral head and not the hip joint's internal rotation mechanism.

**Clinical Pearl / High-Yield Fact**
Perthe's disease is often associated with a history of trauma, such as a fall or direct blow to the hip, which can disrupt the blood supply to the femoral head. Early recognition and treatment are crucial to prevent long-term sequelae, including hip arthritis and degenerative joint disease.

**Correct Answer:** D.