In a study published in the Journal of Anatomy in 2016, Shahar and his co-author described how he had been spotting external occipital protuberances more often in x-rays of relatively young patients at his clinic. To find out more, he looked at 218 radiographs of the lateral cervical spine, where the external occipital protuberance appears, of people aged between 18 to 30-years-old. A growth had to be at least 5mm-long to be counted as an external occipital protuberance, with anything bigger than 10mm classifed as enlarged.
Of the group, 41 percent had the lump, with 10 percent having a spike at least 20mm long. It was more common in men than women, at 67 percent versus 20 percent. The longest was 35.7mm in a man, and 25.5mm in a woman.
This build-up of bone on the external occipital protuberance is a type of enthesophytes.The bony projection on a tendon or ligament is thought to grow gradually over time, so is not expected in young people. Enthesophytes are relatively common in older people.