Cervical rib
A cervical rib in humans is an extra rib which arises from the seventh cervical vertebra.
It is a congenital abnormality located above the normal first rib.
A cervical rib is estimated to occur in 1 in 500 people to 0.5% of the population.
People may have a cervical rib on the right, left or both sides.
Most cases are not clinically relevant and do not have symptoms.
They are generally discovered incidentally.
However, they vary widely in size and shape.
Rarely may cause problems such as contributing to thoracic outlet syndrome, because of pressure on the nerves that may be caused by the presence of the rib.
A cervical rib represents a persistent ossification of the C7 lateral costal element.
In early development, this ossified costal element usually becomes re-absorbed.
When reabsorption fails, it results in an elongated transverse process or complete rib that can be anteriorly fused with the T1 first rib below.
Cervical ribs can be distinguished: their transverse processes are directed inferolaterally, whereas those of the adjacent thoracic spine are directed anterolaterally.
Cervical ribs can cause a form of thoracic outlet syndrome due to compression of the lower trunk of the brachial plexus or subclavian artery:
The brachial plexus or subclavian artery can become encroached upon by the cervical rib and scalene muscles.
Compression of the brachial plexus may be identified by weakness of the muscles around the muscles in the hand, near the base of the thumb.
Compression of the subclavian artery is often diagnosed by a positive Adson’s sign on examination, where the radial pulse in the arm is lost during abduction and external rotation of the shoulder.
A positive Adson’s sign is non-specific for the presence of a cervical rib.
Compression of the sympathetic chain may cause Horner’s syndrome.
Cervical ribs have been connected with leukemia in children