**Core Concept**
The "corner sign" of Park is a radiological feature that refers to a specific appearance of the metaphysis in the distal femur, characterized by a corner-like deformity. This is a sign of osteoporosis and disorganized growth, typically associated with scurvy, a disease caused by vitamin C deficiency.

**Why the Correct Answer is Right**
In scurvy, the corner sign of Park is due to the impaired collagen synthesis and defective bone matrix formation, leading to fragile and weakened bone structure. This results in a characteristic corner-like deformity at the metaphyseal-epiphyseal junction, seen on radiographs. The impaired bone formation and resorption in scurvy lead to a disorganized growth pattern, manifesting as the corner sign.

**Why Each Wrong Option is Incorrect**
* **Option B:** Rickets, caused by vitamin D deficiency, presents with different radiological features, such as cupping and fraying of the metaphyses, and bowing of long bones.
* **Option C:** Battered baby syndrome, also known as shaken baby syndrome, typically shows features of subdural hematoma, retinal hemorrhages, and metaphyseal fractures, but not the corner sign of Park.
* **Option D:** Sickle cell disease is characterized by bone infarcts, dactylitis, and other radiological features, but not the corner sign of Park.

**Clinical Pearl / High-Yield Fact**
The corner sign of Park is a valuable radiological clue for diagnosing scurvy in patients with unexplained bone pain, joint pain, or weakness.

**✓ Correct Answer: A. Scurvy**