Rib Counting Landmarks

Rib counting landmarks

Counting ribs lets examiners put a stethoscope, an ECG electrode, a chest drain or a needle at the right level. Because the 1st rib is hidden behind the clavicle, counting at the front starts at the sternal angle, where the 2nd costal cartilage joins the sternum. At the back, the inferior angle of the scapula and the free tip of the 12th rib give extra starting points.

Anatomical Data

Structure & Landmarks

Articulations	2nd costal cartilage at the sternal angle (manubriosternal joint) Heads and tubercles of the ribs with the thoracic vertebrae posteriorly
Landmarks	Sternal angle and 2nd costal cartilage, the starting point at the front 2nd intercostal space just below it, beside the sternum (aortic area on the right, pulmonary area on the left) 4th intercostal space at the sternal edges (ECG leads V1 and V2) 5th intercostal space in the midclavicular line (apex beat, ECG lead V4) Inferior angle of the scapula over the 7th rib or 7th intercostal space at the back (arm by the side) Free tip of the 12th rib in the posterior flank, used to count upward

Clinical Relevance

Clinical Notes

Chest drains are placed in the 5th intercostal space just in front of the mid-axillary line (the triangle of safety), and needles always pass just above a rib, because the intercostal vein, artery and nerve run in the costal groove under the rib above. The nipple is an unreliable marker, especially in women. Counting up from the 12th rib can mislead when that rib is very short, so the sternal angle is the preferred reference.

Palpation

Find the jugular notch at the top of the sternum and slide your fingers about 5 cm down to the horizontal ridge of the sternal angle. Move sideways onto the 2nd costal cartilage; the soft dip directly below it is the 2nd intercostal space. Walk down one rib and one space at a time with two fingers, staying close to the sternum where the ribs are easiest to feel, then follow the chosen space outward. At the back, the inferior angle of the scapula (arm relaxed at the side) lies over the 7th rib, and the 12th rib can be traced from its free tip in the flank to count upward.

Pathology

Common Injuries & Conditions

Rib Fracture

Most often affects ribs 4-9 near their angles after a fall or blow, causing sharp pain on breathing and coughing and point tenderness over the break.

Intercostal Vessel Injury

A needle or drain passed along the lower border of a rib can tear the intercostal artery and cause bleeding into the chest.

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