Typical ribs

Ribs 2 to 10 are considered typical. Ribs 1, 11 and 12 can be considered atypical.

Gross anatomy

A typical rib is long and flat. They contain a:

• head

• neck

• tubercle

• shaft

• angle

Ribs have a rounded, smooth superior border. The inferior border is thin and sharp. 

Osteology

Head

The head of a rib has two facets.  These two facets are separated by the crest of the head.

Neck

The neck follows the head. It is a narrow portion of the rib found between the head and tubercle. 

Tubercle

The tubercle is found immediately after the neck. It is a prominence on the outer surface of the rib. the tubercle contains a facet that articulates with the transverse process of the numerically corresponding vertebra. This area is called the articular part. The non-articular part provides attachment for the costotransverse ligament.

Shaft (or body)

The lengthy shaft follows the tubercle. It is thin, flat and twisted on the long axis. The shaft bends anteriorly at the angle of the rib. The angle marks the lateral limit of the attachment of the deep muscles of the back to the ribs.

Costal groove

The inferior border contains a groove called the costal groove. The costal groove carries a vein, artery and nerve (mnemonic: VAN) in that order.

Articulations

Vertebrae

Ribs articulate with vertebra by two facets.  The inferior facet articulates with the vertebra below. The superior facet articulates with the numerically corresponding vertebral body above.

The joint capsule is reinforced by the radiate ligament. This ligament has three bands. The upper band extends to the body of the vertebra above. The lower band extends to the vertebra below. The central band runs horizontally, deep to the anterior longitudinal ligament, into the intervertebral disc.

The tubercle articulates with the transverse process also by means of a synovial joint.

Costochondral joint

Every rib articulates with costal cartilage with a cartilaginous joint.

Sternocostal and interchondral joints

Costal cartilages 2 to 7 articulate by their own synovial joints to the lateral border of the sternum.

Ribs 6 to 10 articulate with costal cartilages which then articulate with each other along their borders through small synovial joints.

There are a number of muscles related to typical ribs.

Intercostal muscles

• The intercostal muscles are situated in the intercostal spaces. there are three main groups running superficial to deep:
  • external intercostal muscle
  • internal intercostal muscle
  • inner most intercostal muscle

Diaphragm

• The diaphragm rises from the inner surfaces of the costal cartilages on the sixth rib

Serratus anterior

• The serratus anterior muscles originate anterolaterally from ribs 1 to 8

Pectoralis

• The pectoralis major and minor muscles arise from superior anterior ribs

Latissimus dorsi

• The latissimus dorsi has origins in the 9th to 12th ribs

Scalene muscle group

• Scalenus anterior, posterior and medius muscles have attachments in the first and second ribs

Rectus abdominis

• The rectus abdominis inserts at the xiphisternum and 5th to 7th costal cartilages

Radiographic features

In frontal chest radiographs, 12 pairs of symmetric ribs should be visible. Typical ribs specifically demonstrate a flanged inferior cortex where the costal groove runs.