**Core Concept**
A painless limp in infancy can result from various underlying causes, most of which are related to musculoskeletal or neurological conditions. This symptom requires prompt attention and diagnosis, as it can be a sign of a more serious condition that may require early intervention for optimal outcomes.

**Why the Correct Answer is Right**
A painless limp in infancy can be caused by congenital dislocation of the hip, which occurs when the femoral head does not properly articulate with the acetabulum. Infantile coxa vara, a congenital deformity of the hip where the angle between the femoral neck and shaft is decreased, can also lead to a painless limp. Poliomyelitis, an infectious disease caused by the poliovirus, can result in muscle weakness or paralysis, leading to a painless limp in infants. All of these conditions can cause a painless limp in infancy, making option D the correct answer.

**Why Each Wrong Option is Incorrect**
**Option A:** Congenital dislocation of the hip typically presents with a painful limp, due to the abnormal stress and pressure on the surrounding muscles and joints. However, this is not always the case, and some infants may be asymptomatic.
**Option B:** Infantile coxa vara typically presents with a painful limp, due to the abnormal stress and pressure on the surrounding muscles and joints. However, this is not always the case, and some infants may be asymptomatic.

**Clinical Pearl / High-Yield Fact**
A thorough physical examination, including palpation and range-of-motion testing, is essential in diagnosing the underlying cause of a painless limp in infancy. It is crucial to differentiate between congenital and acquired causes, as the latter may require immediate medical attention.

**Correct Answer:**
✓ Correct Answer: D. All of the above