A cervical rib in humans is an extra rib that arises from the seventh cervical vertebra. Their presence is a congenital abnormality located above the normal first rib. A cervical rib is estimated to occur in 0.2% (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 of cervical ribs are not clinically relevant and do not have symptoms; cervical ribs are generally discovered incidentally. 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 nerves that may be caused by the presence of the rib.
A cervical rib represents a persistent ossification of the C7 lateral costal element. During early development, this ossified coastal 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.