**Core Concept**
Ortolani's test is a clinical examination maneuver used to detect **congenital dislocation of the hip joint** in infants, particularly in the first few months of life. It assesses hip stability by evaluating the reducibility of the femoral head within the acetabulum during passive abduction.

**Why the Correct Answer is Right**
Ortolani's test is performed by gently abducting and flexing the infant’s hip while applying downward pressure on the femoral head. A positive test is indicated by a **sudden "click" or "pop"** due to the reduction of the femoral head from the acetabulum. This movement reflects the presence of a **developmental hip dislocation** (e.g., developmental dysplasia of the hip, DDH), where the femoral head is not properly seated in the acetabulum. The test is most reliable in infants under 6 months due to the high mobility of the hip joint in early development.

**Why Each Wrong Option is Incorrect**
Option A: The knee joint does not undergo Ortolani’s test; congenital dislocation of the knee is extremely rare and not assessed by this maneuver.
Option C: Shoulder dislocation is evaluated using the **Apprehension test** or **Ortolani’s test is not applicable** in shoulder joints.
Option D: Elbow dislocation is assessed by **allis' sign** or **sensation loss**, not Ortolani’s test.

**Clinical Pearl / High-Yield Fact**
Ortolani’s test is a **key early diagnostic tool** for developmental dysplasia of the hip (DDH) in infants. Early detection allows for timely intervention (e.g., Pavlik harness), which significantly improves outcomes and prevents long-term disability.

✓ Correct Answer: B. Congenital dislocation of the hip joints