**Core Concept**
Congenital dislocation of the hip (CDH) is a condition where the femoral head is not properly seated in the acetabulum, leading to instability and dislocation. The Ortolani and Barlow maneuvers are clinical tests used to diagnose CDH.

**Why the Correct Answer is Right**
The Ortolani sign is a clinical test used to diagnose congenital dislocation of the hip. When the knees and hips are flexed to 90 degrees, the affected thigh is at a lower level compared to the normal side. This is because the femoral head is not properly seated in the acetabulum, resulting in a decrease in the acetabular coverage. The Ortolani sign is a key indicator of CDH, and it is often used in conjunction with the Barlow maneuver to diagnose the condition.

**Why Each Wrong Option is Incorrect**
**Option A:** This option does not describe a known clinical sign for congenital dislocation of the hip.
**Option B:** The Ortolani sign is a specific clinical test used to diagnose CDH, and it is not related to the Barlow maneuver, which is a different test.
**Option C:** This option does not accurately describe the Ortolani sign, which involves flexion of the knees and hips to 90 degrees.

**Clinical Pearl / High-Yield Fact**
It is essential to perform the Ortolani and Barlow maneuvers in infants under 6 months of age to diagnose congenital dislocation of the hip. These maneuvers should be performed by an experienced healthcare provider to ensure accurate diagnosis and treatment.

**Correct Answer:** C. Ortolani sign.