First Rib
Costa Prima
location_on Uppermost rib, at the thoracic inlet between the manubrium and T1 vertebra
The first rib is the shortest, broadest, and most curved of all the ribs, forming the superior boundary of the thoracic cage. Unlike other ribs, it has broad flat superior and inferior surfaces rather than internal and external surfaces. It bears grooves for the subclavian artery and vein and the scalene tubercle for the scalenus anterior muscle. First rib fractures indicate extremely high-energy trauma and are associated with major vascular injury.
Key Anatomical Features
- Broadest and most curved rib with flat superior and inferior surfaces
- Scalene tubercle on the superior surface separates the subclavian vein (anterior) from the subclavian artery (posterior)
- Groove for the subclavian artery lies behind the scalene tubercle
- Groove for the subclavian vein lies in front of the scalene tubercle
- Single articular facet on the head (articulates only with T1, not two vertebrae)
- Costal cartilage articulates directly with the manubrium (synchondrosis)
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Scalenus anterior | Scalene tubercle on superior surface | Elevates the first rib during forced inspiration and flexes the neck |
| Scalenus medius | Superior surface posterior to the subclavian groove | Elevates the first rib during forced inspiration |
| Subclavius | Junction of first rib and its costal cartilage | Depresses the clavicle and protects the subclavian vessels |
| Serratus anterior (first digitation) | Outer border | Protracts the scapula |
| Intercostalis intimus (first intercostal space) | Inner surface of first rib | Stabilizes the intercostal space |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| First costovertebral joint | Synovial plane (single facet) | T1 vertebral body only |
| First costotransverse joint | Synovial plane | Transverse process of T1 |
| First sternocostal joint | Synchondrosis (primary cartilaginous) | Manubrium of sternum |
Common Pathologies
First rib fracture
Indicates extremely high-energy trauma due to the rib's protected position. Associated with subclavian vessel injury, brachial plexus damage, and intrathoracic injuries in up to 60% of cases.
Thoracic outlet syndrome
Compression of the brachial plexus, subclavian artery, or subclavian vein between the first rib and clavicle or scalene muscles. A cervical rib (supernumerary rib from C7) can exacerbate this.
First rib stress fracture
Rare overuse fracture seen in overhead athletes (pitchers, rowers) from repetitive scalene muscle traction. Can mimic thoracic outlet syndrome symptoms.
Clinical Relevance
First rib fracture on a chest X-ray should trigger evaluation for major vascular injury (subclavian artery and vein) and brachial plexus injury. CT angiography is recommended. Thoracic outlet syndrome can be neurogenic (most common, brachial plexus compression), venous (Paget-Schroetter syndrome), or arterial. First rib resection is a definitive surgical treatment for thoracic outlet syndrome.
Development and Ossification
The first rib ossifies from three centers like other ribs but has a single head facet because it articulates with only one vertebral body (T1). The costal cartilage of the first rib is the only one that forms a synchondrosis (primary cartilaginous joint) with the sternum rather than a synovial joint.
Did You Know?
- The first rib is the only rib that lies horizontally, with flat upper and lower surfaces instead of inner and outer surfaces
- The scalene tubercle on the first rib was described by the French anatomist Lisfranc, the same surgeon who described the midfoot joint
- First rib fractures are relatively rare and almost always indicate severe trauma, often from high-speed motor vehicle collisions
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