**Core Concept:**
Congenital dislocation of the hip (CDH) is a condition where the baby's hip joint is unstable or completely dislocated at birth. Early diagnosis is crucial to prevent permanent damage to the joint and muscles surrounding it. The following tests are used to diagnose CDH:

**Why the Correct Answer is Right:**
The correct answer is **D** - **Orthopedic Examination**. This is because the diagnosis of CDH relies heavily on clinical examination skills in a pediatrician or orthopedic surgeon. They must be able to assess the joint stability by checking for:

1. **Active flexion and abduction limitation:** This is the most common sign in CDH and indicates that the hip cannot move freely.
2. **Deformity of the thigh:** If the thigh appears shorter or more flexed than the other side, it may indicate a dislocated hip.
3. **Decreased motion of the hip:** If the physician is unable to move the hip joint easily, it may be a sign of dislocation or instability.

**Why Each Wrong Option is Incorrect:**

A. **X-ray:** While X-rays can confirm CDH, the correct answer is **D** - **Orthopedic Examination** because the physical examination allows for the detection of early signs of the condition. X-rays are typically ordered after clinical suspicion has been raised and can provide further confirmation.

B. **Ultrasound:** Though ultrasound can be useful in detecting CDH, the primary method of diagnosis is **D** - **Orthopedic Examination**. Ultrasound is often performed after clinical suspicion has been raised and can provide more detailed images of the joint.

C. **Physical examination:** This option is incorrect because the core concept requires the use of specialized examination techniques to diagnose CDH. While a physical examination is essential, the correct answer is **D** - **Orthopedic Examination** because it is the initial step in detecting CDH and guides further diagnostic steps, like X-rays and ultrasounds.

**Clinical Pearl:**

In clinical practice, the physician should perform a thorough physical examination of the hip joint in newborns and infants, paying special attention to the signs mentioned above: active flexion and abduction limitation, deformity of the thigh, and decreased motion of the hip. This will help identify infants who require further diagnostic steps, such as X-rays and ultrasounds, for definitive diagnosis and appropriate management.