A cervical rib in humans is an extra rib which arises from the seventh

cervical vertebra In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...

. Their presence is a

congenital A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities c ...

abnormality located above the normal first rib. A cervical rib is estimated to occur in 0.2% to 0.5% (1 in 200 to 500) of the population. People may have a cervical rib on the right, left or both sides. Most cases of cervical ribs are not clinically relevant and do not have symptoms; cervical ribs are generally discovered incidentally, most often during

x-ray X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...

s and

CT scan A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...

s. However, they vary widely in size and shape, and in rare cases, they may cause problems such as contributing to thoracic outlet syndrome, because of pressure on the

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...

s that may be caused by the presence of the rib. A cervical rib represents a persistent

ossification Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in ...

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.

Diagnosis

On imaging, cervical ribs can be distinguished because their transverse processes are directed inferolaterally, whereas those of the adjacent thoracic spine are directed anterolaterally.

Associated conditions

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 The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...

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 in the hand, near the base of the thumb. Compression of the subclavian artery is often diagnosed by finding a positive

Adson's sign Adson's sign is the loss of the radial pulse in the arm by rotating head to the ipsilateral side with extended neck following deep inspiration. It is sometimes used as a sign of thoracic outlet syndrome (TOS). It is named after Alfred Washington ...

on examination, where the radial

pulse In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the ...

in the arm is lost during

abduction Abduction may refer to: Media Film and television * "Abduction" (''The Outer Limits''), a 2001 television episode * " Abduction" (''Death Note'') a Japanese animation television series * " Abductions" (''Totally Spies!''), a 2002 episode of an ...

and external rotation of the

shoulder The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder m ...

. 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. Compression of the sympathetic chain may cause

Horner's syndrome Horner's syndrome, also known as oculosympathetic paresis, is a combination of symptoms that arises when a group of nerves known as the sympathetic trunk is damaged. The signs and symptoms occur on the same side (ipsilateral) as it is a lesion ...

Other animals

Many vertebrates, especially

reptiles Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephali ...

, 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 ''Mamenchisaurus'' (or spelling pronunciation ) is a genus of sauropod dinosaur known for their remarkably long necks which made up nearly half the total body length. Numerous species have been assigned to the genus; however, many of these might ...

'' were nearly 4 meters long. In

birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

, the cervical ribs are small and completely fused to the vertebrae. In mammals, the ventral parts of the

transverse processes The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

of the

e 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 had increased the number of mammoths being born with cervical ribs. Cervical ribs have been connected with

leukaemia Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ...

in human children, so it has given scientists new evidence to believe that the mammoth's extinction was attributed to the condition.

References

External links

{{DEFAULTSORT:Cervical Rib Supernumerary body parts Congenital disorders of musculoskeletal system Human anatomy