The thorax contains 12 pairs of ribs, 12 thoracic vertebrae, and the sternum. The ribs articulate posteriorly with the vertebral column [1]. Anteriorly, the costal cartilages of the first ribs attach directly to the manubrium by synchondroses, the second through seventh ribs articulate with the manubrium or body of the sternum by synovial cavities, and the eighth through 10th ribs form a synchondrosis with the seventh costal cartilage. The 11th and 12th ribs are often referred to as floating ribs because they end blindly in the anterior abdominal wall [2].

At either side of the suprasternal notch is the sternoclavicular joint, a double diarthrodial (synovial) joint bisected by an articular disk (Fig. 1). A prominent transverse ridge at the manubriosternal joint—the sternal angle or the angle of Louis—forms a palpable landmark for the second costal cartilages and, indirectly, the level of the T4-T5 intervertebral disk [1] (Fig. 2).

The posterior end of each rib is composed of a head, neck, and tubercle. The head articulates with the corresponding vertebra, forming the costovertebral joint. The tubercle, a bony protuberance on the posterior surface of the rib, articulates with the transverse process of the vertebra, forming the costotransverse joint (Fig. 3). The costal groove on the inferomedial aspect of the rib contains the intercostal vessels and nerves.

Calcification of the costal cartilages tends not to be radiographically apparent in most healthy patients younger than 35 years. Before that age, calcification of the costal cartilages may be associated with chronic renal failure, thyroid disease, autoimmune disorders, and chondrosarcoma [2]. The normal patterns of calcification differ between males and females, usually appearing as peripheral parallel lines in males (Fig. 4A,) and as central, globular clumps in females (Fig. 4B).

Fractures are the most common lesions to affect the ribs overall [9]. Acute rib fractures may be radiographically occult and even subtle on CT. Fatigue-type stress fractures in the ribs may be associated with sporting activities such as rowing, golf, or other activities that cause repetitive stress [9]. Insufficiency-type stress fractures may be found in association with chronic osteopenia or osteomalacia. Bone scintigraphy has a high negative predictive value for stress fractures (Figs. 17A, and 17B).

Septic arthritis is most often due to hematogenous spread of Staphylococcus aureus originating from a skin lesion. In adults, the sternoclavicular and sacroiliac joints, symphysis pubis, and spine are most frequently affected [10]. Infection may also involve the ribs in places such as the costosternal junction (Fig. 18). CT findings may include soft-tissue edema, articular erosion, joint effusion, subchondral bone destruction, and reactive sclerosis.

Ankylosing spondylitis is a chronic inflammatory arthritis that involves predominantly the sacroiliac, apophyseal, diskovertebral, costovertebral, and costotransverse articulations [13]. Early changes in the costovertebral and costotransverse joints include indistinctness of the subchondral bone, and, in the costovertebral joint, sclerosis that is most evident on the vertebral side [13, 14] (Fig. 21). The changes ultimately progress to bony ankylosis.

The ribs are involved in a variety of traumatic, metabolic, inflammatory, neoplastic, and congenital disorders. CT is useful to further characterize a rib lesion found on radiography or bone scintigraphy. A rib lesion inadvertently discovered on a CT examination of the chest may be the first sign of a systemic disorder or a remote primary neoplasm.

Address correspondence to L. L. Seeger ([email protected]).