Can External Occipital Protrusion Be the Cause of Shoulder Pain?

The external occipital protuberance (EOP) can sometimes be felt as a palpable swelling and sometimes as a protrusion extending downward. It is also called an inion hook. EOP bony tubercle can be generally classified into three types: flat form (type 1), crest type (type 2), and protrusion type (type 3). In this report, we present a 32-year-old adult male patient with right shoulder pain. On examination, pain extending from the occipital region to the shoulder was observed. Type 3 EOP protrusion was incidentally detected on X-ray imaging. When “EOP” was searched in PubMed, anatomical and imaging studies were found. It was found to be clinically associated with headache in studies in terms of size and type. We think that this is the first case of EOP protrusion associated with shoulder pain.