Counting ribs is a useful skill in various medical fields, particularly in radiology and physical examination. The following methods can be used to accurately count ribs:
1. Using the Angle of Louis:
- The angle of Louis, also known as the sternal angle, is a prominent bony landmark located at the junction of the manubrium and the body of the sternum.
- It corresponds to the level of the second rib.
- Start counting ribs from the angle of Louis, moving downwards.
2. Counting Posterior Ribs:
- This method involves counting ribs on the back, starting at the lower back.
- The inferior angle of the scapula generally sits on the 7th rib posteriorly.
- Count upwards from this landmark.
3. Using Computed Tomography (CT):
- CT scans provide detailed cross-sectional images of the chest.
- While useful for detecting lesions, counting ribs on CT can be challenging due to the complex anatomy.
- Specialized methods, like the Modified Sternoclavicular Method, can be employed for more accurate counting.
4. On a Chest X-ray:
- The clavicles, ribs, scapulae, spine, and proximal humeri (upper arms) are visible on a chest X-ray.
- Counting ribs can be easier on a lateral chest radiograph, where the sternal angle or the 12th rib can be used as starting points.
Important Notes:
- Most people have 12 ribs on each side of their body, totaling 24 ribs.
- Rib variations do exist, and these may affect the accuracy of counting.
Example:
If you are counting ribs from the angle of Louis, and you reach the fourth rib, you know that the three ribs above it are the first, second, and third ribs.
