Cervical rib

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Cervical rib
Classification and external resources
ICD-10 Q76.5
ICD-9 756.2
OMIM 117900
DiseasesDB 2317
3D CT reconstruction of a cervical rib.

A cervical rib in humans is a supernumerary (or extra) rib which arises from the seventh cervical vertebra. Sometimes known as "neck ribs",[1] their presence is a congenital abnormality located above the normal first rib. A cervical rib is present in only about 1 in 500 (0.2%) of people;[2] in even rarer cases, an individual may have two cervical ribs.

A cervical rib represents a persistent ossification of the C7 lateral costal element. During early development, this ossified costal element typically becomes re-absorbed. Failure of this process results in a variably elongated transverse process or complete rib that can be anteriorly fused with the T1 first rib below. [3]

Associated conditions[edit]

The presence of a cervical rib can cause a form of thoracic outlet syndrome due to compression of the lower trunk of the brachial plexus or subclavian artery. These structures 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 finding 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 however, as many individuals without a cervical rib will have a positive test.

Other animals[edit]

Many vertebrates, especially reptiles, have cervical ribs as a normal part of their anatomy rather than a pathological condition. Some sauropods had exceptionally long cervical ribs; those of Mamenchisaurus hochuanensis were nearly 4 meters long.

In birds, the cervical ribs are small and completely fused to the vertebrae.

In mammals the ventral parts of the transverse processes of the cervical vertebrae are the fused-on cervical ribs.

Recent studies have also found a high percent of cervical ribs in woolly mammoths. It is believed that the decline in mammoth numbers may have forced inbreeding within the species which in turn has increased the number of mammoths being born with cervical ribs. Cervical ribs have been connected with leukaemia in children (humans), so it has given scientists new evidence to believe that the mammoth's extinction was attributed to the condition [4]

Anatomy diagrams[edit]