First rib

The first rib is the most superior of the twelve ribs. It is an atypical rib and is an important anatomical landmark and is one of the borders of the superior thoracic aperature. 

Gross anatomy

Osteology

Compared to a typical rib because the first rib is short and thick and it has single articular facet for the costovertebral joint. The first rib has a head, neck and shaft but lacks a discrete angle. The shaft is indented laterally, the groove for the subclavian artery, which contains the lowest brachial plexus trunk as well as the subclavian artery. Anterior to the scalene tubercle is another groove for the subclavian vein. There is no costal groove on its inferior surface. It has two tubercles:

• transverse tubercle:posterior and lateral to the neck; bears an articular facet for the transverse process of T1
• scalene tubercle: anteriorly between the grooves for the subclavian artery and vein; anterior scalene muscle inserts here

Articulations

• costovertebral joint: articular facet on head of the rib with single articular facet
• costotransverse joint: articular facet on transverse tubercle with transverse process of T1 
• costochondral joint: distal shaft with first costal cartilage

Attachments

• anterior scalene muscle: scalene tubercle
• middle scalene muscle: between groove for the subclavian artery and scalenetransverse tubercle
• intercostal muscles: from the outer border
• subclavius muscle: arises from distal shaft and first costal cartilage
• first digitation of the serratus anterior muscle
• parietal pleura: from the inner border
• costoclavicular ligament: anterior to the groove for the subclavian vein

Relations

• superiorly: lower trunk of the brachial plexus; subclavian vessels; clavicle
• inferiorly: intercostal vessels and nerves; parietal pleura
• anteriorly: sympathetic trunk (over neck); superior intercostal artery; ventral T1 nerve root

Variant anatomy

• ossesous or fibrous articulation or fusion with a cervical rib
• bifid (forked) rib
• rudimentary (hypoplastic) rib: most commonly the first rib (0.2%) ⁶
• pseudoarthrosis of the first rib (0.1%) ⁶

Related pathology

The first rib in particular is involved in:

• thoracic outlet syndrome
• Pancoast tumour (this may also affect other superior ribs)

The first rib is also affected by pathology common to all ribs:

• infection, e.g. septic arthritis, osteomyelitis
• malignancy, e.g. chondrosarcoma, enchondroma, metastases
• trauma, e.g. fracture
  • first rib fractures are often associated with clavicle fractures or damage to adjacent neurovascular structures