Cervical rib is an extra rib that arises from the 7th cervical vertebrae. It is a congenital anomaly present in 0.2% of the population. Most of them are unilateral but a small % are bilateral.
Most patients are asymptomatic. Some present with thoracic outlet obstruction due to compression of brachial plexus. This presents as weakness of the muscles of the hand in particular the base of the thumb.