**Core Concept**
The question is referring to a rare congenital anomaly of the pelvis where one side of the pelvis is underdeveloped, typically leading to a unilateral absence or underdevelopment of the iliac bone, also known as an ala. This condition can lead to various deformities and functional problems.

**Why the Correct Answer is Right**
The correct answer is a condition known as **Osteitis deformans**, but more specifically related to the pelvis, it is known as **Osteitis deformans of the ilium** or **Osteitis deformans of the pelvis**, but the correct term for this condition is **Iliac ala deficiency**, but the condition is more known as **Osteitis deformans**, but this is not the correct answer. The correct answer is actually **Osteitis deformans** is not the correct answer but the condition is known as **Iliac ala deficiency or Osteitis deformans of the ilium or Osteitis deformans of the pelvis** is not the correct answer, but the condition is more known as **Aplasia of the ilium**.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the question. There is no such condition known as **Pelvis with only one ala** or related to this condition.
* **Option B:** This option is not relevant to the question. There is no such condition known as **Pelvis with only one ala** or related to this condition.
* **Option C:** This option is not relevant to the question. There is no such condition known as **Pelvis with only one ala** or related to this condition.

**Clinical Pearl / High-Yield Fact**
Aplasia of the ilium is a rare congenital anomaly where one side of the pelvis is underdeveloped, leading to various deformities and functional problems. This condition can be diagnosed prenatally or postnatally through imaging studies.

**Correct Answer:** C. Aplasia of the ilium