Correct answer: Cervical rib. A cervical rib is present in only about 1 in 500 (0.2%) of people; in even rarer cases, an individual may have two cervical ribs. Patients sometimes visit their doctor complaining of neck pain or stiffness, after which the 'neck ribs' are found by accident. The genetic cause isn't well understood, but it has probably something to do with HOX-genes.