What is the anatomical landmark used to count ribs and intercostal spaces on a chest exam?

• A. The sternum and its manubrium; the sternal angle (Angle of Louis)
• B. The clavicle
• C. The spine
• D. The xiphoid process

Answer: (A)

Counting ribs and intercostal spaces on a chest exam relies on a stable, palpable midline landmark that marks the level of the second rib: the sternal angle (Angle of Louis), where the manubrium meets the body of the sternum. This point is easy to feel along the sternum and corresponds to the attachment of the second costal cartilage, making it the reliable zero point for rib counting. From there, you can identify the second rib at that level and count upward to locate the first intercostal space just above it, and count downward for lower spaces. The sternum is the central chest bone, so using this landmark is more reliable than other surface features. The clavicle sits above and laterally and isn’t a consistent rib-counting reference, the spine is posterior and not accessible for this purpose, and the xiphoid process is far below and variable, so it isn’t used for rib counting.