**Core Concept**
Rickets is a disease caused by vitamin D deficiency, leading to impaired bone mineralization and growth retardation in children. It is characterized by softening of the bones, which can result in skeletal deformities and other complications.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of rickets. Rickets is caused by a deficiency in vitamin D, which is essential for calcium absorption and bone mineralization. In rickets, the lack of vitamin D leads to softening of the bones, causing them to become bowed or deformed. The correct answer is a feature that is not typically seen in rickets.

**Why Each Wrong Option is Incorrect**
* **Option A:** Osteopenia is a condition characterized by a decrease in bone mass and density, which can be seen in rickets due to impaired bone mineralization.
* **Option B:** Delayed bone age is a common feature of rickets, as the disease affects the growth plates and bone development.
* **Option C:** Rachitic rosary, also known as a rachitic rosary, is a characteristic feature of rickets, where the costochondral junctions are enlarged and visible, giving a rosary-like appearance.

**Clinical Pearl / High-Yield Fact**
One important aspect of rickets is that it can be prevented and treated with vitamin D supplementation, calcium and phosphate supplementation, and adequate sunlight exposure. It is essential to diagnose and treat rickets early to prevent long-term complications.

**Correct Answer: D.**