**Core Concept**
Cubitus varus, also known as gunstock deformity, is a common complication of supracondylar fractures of the humerus in children. It is characterized by a varus (inward) angulation of the elbow joint, resulting in a abnormal alignment of the forearm and arm.

**Why the Correct Answer is Right**
The preferred treatment of cubitus varus is corrective osteotomy, which involves surgically cutting and realigning the bone to restore normal alignment and function. This procedure is usually performed in children between the ages of 2 and 5 years, when the bone is still pliable and easier to correct. The goal of the surgery is to restore a normal carrying angle, improve forearm and arm function, and prevent long-term complications such as limited range of motion, pain, and joint degeneration.

**Why Each Wrong Option is Incorrect**
**Option A:** Casting and splinting are not effective in correcting cubitus varus, as the deformity is due to a bony malalignment that cannot be corrected by external immobilization alone.
**Option B:** Observation is not a suitable treatment for cubitus varus, as the deformity can lead to long-term complications and functional impairment if left untreated.
**Option C:** Arthroscopic surgery is not typically used to treat cubitus varus, as the deformity involves bony malalignment rather than soft tissue pathology.

**Clinical Pearl / High-Yield Fact**
In children with cubitus varus, it is essential to monitor for signs of long-term complications, such as limited range of motion, pain, and joint degeneration, which can occur even after successful surgical correction.

**Correct Answer:** C. Corrective osteotomy