Ribs
Costae
location_on Thoracic cage, curving from the thoracic vertebrae posteriorly to the sternum anteriorly
The 12 pairs of ribs form the lateral walls of the thoracic cage, protecting the heart, lungs, and great vessels. Ribs 1-7 are true ribs (connecting directly to the sternum via costal cartilage), ribs 8-10 are false ribs (connecting to the sternum indirectly via the cartilage above), and ribs 11-12 are floating ribs (no anterior attachment). Each typical rib has a head, neck, tubercle, and a long curved body with a costal groove sheltering the intercostal neurovascular bundle.
Key Anatomical Features
- Head has two articular facets for articulation with two adjacent vertebral bodies
- Costal groove on the inferior internal surface shelters the intercostal vein, artery, and nerve (VAN order from above)
- Angle of the rib is the point of maximum curvature and a common fracture site
- First rib is the shortest, broadest, and most curved, with grooves for the subclavian vessels
- Costal cartilage connects the bony rib to the sternum and allows elastic recoil during breathing
- Tubercle articulates with the transverse process of the corresponding vertebra (ribs 1-10)
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| External intercostals | Inferior border of rib above to superior border of rib below | Elevate ribs during inspiration |
| Internal intercostals | Superior border of rib below to inferior border of rib above | Depress ribs during forced expiration |
| Serratus anterior | Outer surfaces of ribs 1-8 | Protracts the scapula |
| Diaphragm | Inner surfaces of costal cartilages 7-12 | Primary muscle of inspiration |
| Scalenes | First and second ribs | Elevate the first two ribs during forced inspiration |
| External oblique | Outer surfaces of ribs 5-12 | Flexes and rotates the trunk |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Costovertebral joints | Synovial plane | Thoracic vertebral bodies |
| Costotransverse joints | Synovial plane | Transverse processes of T1-T10 |
| Sternocostal joints | Synovial (2-7) and synchondrosis (1st) | Sternum via costal cartilage |
Common Pathologies
Rib fracture
The most common thoracic injury, usually affecting ribs 4-10 at the angle. Multiple rib fractures can cause flail chest. First rib fracture indicates severe trauma and possible vascular injury.
Flail chest
Three or more consecutive ribs fractured in two or more places, creating a free-floating segment that moves paradoxically during breathing. Causes significant respiratory compromise.
Cervical rib
Supernumerary rib arising from C7, present in about 0.5% of the population. Can cause thoracic outlet syndrome by compressing the brachial plexus or subclavian vessels.
Costochondritis
Inflammation of the costal cartilage causing anterior chest pain that mimics cardiac pain. The second to fifth costochondral junctions are most commonly affected.
Clinical Relevance
Rib fractures are the most common injury in blunt chest trauma. The intercostal neurovascular bundle runs in the costal groove along the inferior border of each rib, so thoracentesis and chest tube insertion should be performed just above the upper border of the rib below. Fractures of ribs 9-12 should prompt evaluation for liver (right) or splenic (left) injury. First and second rib fractures indicate very high-energy trauma.
Development and Ossification
Each rib ossifies from three centers: one for the body (appearing around the 8th fetal week), one for the head, and one for the tubercle (the latter two appearing at puberty and fusing by age 25). The costal cartilages may calcify in adulthood, with patterns that differ between sexes, useful in forensic age and sex estimation.
Did You Know?
- Humans almost always have 12 pairs of ribs, but about 1 in 200 people has a 13th pair (lumbar ribs)
- Contrary to popular belief, men and women have the same number of ribs
- The costal cartilage ossification pattern is so distinctive it can be used to estimate age and sex in forensic cases
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