What is the standard centering for the AP coccyx projection?

• A. Center approximately 2 inches above the pubic symphysis with a 10-degree caudad angle
• B. Center 2 inches below the pubic symphysis with a 10-degree cephalad angle
• C. Center at the pubic symphysis with 0-degree angle
• D. Center 4 inches above the pubic symphysis with a 20-degree caudad angle

Answer: (A)

AP coccyx imaging uses an axial setup to bring the coccyx into view by reducing pelvic bone overlap. Since the coccyx sits just above the pubic symphysis, centering the CR about two inches superior to the pubic symphysis aligns the beam with the coccygeal region. A caudad angle of roughly 10 degrees tilts the rays downward, helping to project the coccyx away from the pelvic bones and improving its visibility and the clarity of the sacrococcygeal joint. Centering lower or higher, or using a different angulation, would either miss the coccyx or worsen superimposition, making this combination the standard choice.