**Core Concept**
Perthes 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 its collapse and deformity. The disease typically affects children between the ages of 4 and 10.

**Why the Correct Answer is Right**
Perthes disease is typically diagnosed using radiographic imaging. The characteristic X-ray features of Perthes disease include a "crescent sign" or "crescent-shaped" area of lucency (bone loss) in the femoral head, representing the area of avascular necrosis. Other features may include a "flaked" or "chipped" appearance of the femoral head, representing fragmentation of the bone, and a "sclerosis" of the surrounding bone, indicating reactive bone formation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a characteristic X-ray feature of Perthes disease. While some bone lesions may exhibit "moth-eaten" borders, this term is more commonly associated with other conditions, such as metastatic bone disease.
**Option B:** This option is not a specific X-ray feature of Perthes disease. While some bone lesions may exhibit "ground-glass" appearance, this term is more commonly associated with conditions such as Paget's disease or fibrous dysplasia.
**Option C:** This option is not a characteristic X-ray feature of Perthes disease. While some bone lesions may exhibit "lytic" lesions, this term is more commonly associated with conditions such as multiple myeloma or osteoclastoma.

**Clinical Pearl / High-Yield Fact**
Perthes disease is a childhood hip disorder with a characteristic "crescent sign" on X-ray. Remember the "C3" features of Perthes disease: Crescent-shaped lucency, Chipped or flaked appearance of the femoral head, and Sclerosis of the surrounding bone.

**Correct Answer: A. Crescent sign**