Cervical Rib
Costa Cervicalis
location_on Arising from the C7 vertebra, extending into the lower neck above the first rib
A cervical rib is a supernumerary (extra) rib arising from the seventh cervical vertebra, present in approximately 0.5-1% of the population. It may be a fully formed rib reaching the sternum, a partial bony projection, or a fibrous band. Though most are asymptomatic, a cervical rib is the most well-known cause of thoracic outlet syndrome, where it compresses the brachial plexus or subclavian vessels between the rib and the scalenus anterior muscle.
Key Anatomical Features
- Supernumerary rib arising from the transverse process of C7
- Ranges from a small bony projection to a complete rib reaching the manubrium
- Present in 0.5-1% of the population, bilateral in 50-70% of cases
- More common in females and often discovered incidentally on chest X-ray
- A fibrous band from the tip of an incomplete cervical rib can still cause compression
- Narrows the thoracic outlet between the scalene muscles and the first rib
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Scalenus anterior | May attach to cervical rib instead of or in addition to the first rib | Elevates the rib during inspiration and flexes the neck |
| Scalenus medius | May attach to cervical rib | Elevates the rib during inspiration |
| Subclavian artery | Passes over or is displaced by the cervical rib | N/A (vascular structure compressed by the rib) |
| Brachial plexus | Lower trunk (C8-T1) may be compressed against the rib | N/A (neural structure compressed by the rib) |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Costovertebral joint (C7) | Synovial plane or fibrous | C7 vertebral body and transverse process |
| Costocostal joint (variable) | Fibrous or bony fusion | First rib (when complete) |
| Costomanubrial joint (rare) | Synchondrosis (when fully formed) | Manubrium (rare, only with complete cervical rib) |
Common Pathologies
Neurogenic thoracic outlet syndrome
Compression of the lower trunk of the brachial plexus (C8-T1) causing pain, numbness, and weakness in the hand (especially ulnar distribution). Accounts for 95% of TOS cases.
Arterial thoracic outlet syndrome
Compression of the subclavian artery causing arm ischemia, Raynaud-like symptoms, and risk of aneurysm and distal embolization. A vascular emergency when symptomatic.
Venous thoracic outlet syndrome (Paget-Schroetter)
Compression of the subclavian vein causing effort thrombosis with acute arm swelling and cyanosis, typically in young active individuals.
Subclavian steal phenomenon (rare)
In rare cases, a cervical rib can contribute to subclavian artery stenosis leading to retrograde vertebral artery flow during arm exercise.
Clinical Relevance
Most cervical ribs are asymptomatic and are incidental findings on chest X-rays. Symptomatic cervical ribs require thorough neurovascular assessment including Adson test (loss of radial pulse with head turned to the affected side), Roos test (arm elevation and hand opening/closing for 3 minutes), and vascular studies. Surgical resection of the cervical rib (and sometimes the first rib) is the definitive treatment for symptomatic thoracic outlet syndrome. An incomplete cervical rib with a fibrous band can be as symptomatic as a complete one.
Development and Ossification
A cervical rib develops from persistence and growth of the costal element of the C7 vertebra, which normally regresses during fetal development. The genetic basis involves mutations in HOX genes that control the cervical-thoracic transition. It is classified as a congenital anomaly of segmentation.
Did You Know?
- About 0.5-1% of people have a cervical rib, but only about 10% of those develop symptoms
- Cervical ribs are bilateral in more than half of cases, though symptoms are usually unilateral
- The cervical rib has been recognized since the time of Galen in the 2nd century AD
Scan this bone yourself
Download Osteo+ and identify the cervical rib instantly with your camera. Get all the details above and more from a single photo.