Check for abnormalities of single bones and for diffuse bone disease
The bones are helpful in assessing the quality of the chest X-ray
Bones are the densest tissue visible on a normal chest X-ray. Despite this, it is easy to overlook important abnormalities of the bones, which may be very subtle.
The bones visible on a chest X-ray include the clavicles, the ribs, the scapulae, part of the spine, and the proximal humeri (upper arms). Of these only the clavicle is seen in entirety. The sternum is also included on a frontal view, but overlies other midline structures and so is obscured.
The bones are used as useful markers of chest radiograph quality. They are used to assess patient rotation, adequacy of inspiration and X-ray penetration.
The ribs play a role in assessing the adequacy of inspiration taken by the patient. The anterior end of approximately 5-7 ribs should be visible above the diaphragm in the mid-clavicular line. Less than this indicates an incomplete breath in, and more than 7 ribs or flattening of the diaphragm, suggests lung hyper-expansion.
On this normal X-ray the anterior end of the 7th rib (asterisk) intersects the diaphragm at the mid-clavicular line.
This chest X-ray also demonstrates the subcostal grooves (red highlights) on the underside of the ribs. These grooves contain the neurovascular bundles that accompany each rib. To avoid damaging the nerves or vessels, the superior edge of a rib is used as the landmark for needle insertion during procedures such as chest drain insertion.
Note: The spine can be seen through the heart, indicating adequate X-ray penetration.
Assessing the bones
Bones are useful for the initial assessment of image quality, and offer useful information regarding rotation, inspiration and penetration.
Acute rib fractures are often invisible, therefore chest X-rays are not helpful if there is clinical suspicion of a rib injury, unless complications such as pneumothorax are suspected.
Occasionally you will see an important abnormality of the bones on a chest X-ray such as a metastatic deposit. These may be seen in the bones at the edge of the image such as the scapula or proximal humerus. Therefore, always look carefully at all the bones when viewing a chest X-ray.