**Core Concept**
Madelung's deformity is a rare congenital anomaly characterized by a specific abnormality of the forearm bones. It is a type of skeletal dysplasia that affects the distal radius, leading to characteristic changes in the bone's shape and structure.

**Why the Correct Answer is Right**
Madelung's deformity involves the distal radius due to an abnormality in the growth and development of the bone. The deformity typically presents with a short, broad distal radius, which can cause symptoms such as pain, limited mobility, and functional impairment. The affected bone may also exhibit a characteristic "beaking" or "cupping" appearance on radiographic examination. This deformity is often associated with an abnormality in the growth plate of the distal radius, which can be caused by a genetic mutation or other underlying condition.

**Why Each Wrong Option is Incorrect**
**Option A:** The humerus is not typically involved in Madelung's deformity.
**Option B:** While the proximal ulna may be affected in some cases of Madelung's deformity, it is not the primary bone involved in this condition.
**Option D:** The carpals are bones in the wrist, and Madelung's deformity specifically involves the forearm bones, not the wrist bones.

**Clinical Pearl / High-Yield Fact**
Madelung's deformity often presents with a characteristic "beaking" or "cupping" appearance on radiographic examination, which can be a useful diagnostic clue for this condition.

**✓ Correct Answer: C. Distal radius**