Morphological features related to the enlargement of the external occipital protuberance

Purpose The cause of enlarged external occipital protuberance (EEOP) is thought to be mechanical stress on the head and neck, but the exact cause remains unclear. Therefore, in this study, we investigated the morphological features of EEOP using human dry bones, skulls, cervical vertebrae, and scapulae, and considered its cause. Methods The study involved 300 dried bones, with an average age at death of 66.8 years, all male. We investigated EEOP; osteophyte in the sixth vertebral body (C6-osteophyte); subacromial osteophyte (SA-osteophyte); the skull circumference; and the anterior–posterior (AP) and right-left (RL) diameters of the sixth cervical vertebral body (C6). The group with positive EEOP was labeled the EEOP ( +) group, and the group with negative EEOP was the EEOP (-) group. A comparative study was carried out between the two groups. Results The statistical analysis revealed that the prevalence of C6-osteophyte was significantly higher ( p = 0.0004) in the EEOP ( +) group than in the EEOP(-) group. There was no significant difference in age, SA-osteophyte, skull circumference, and AP and RL diameters of C6 between the two groups. Conclusion The authors report the significant presence of C6-osteophytes in individuals with EEOP( +). This is the first morphological study to report a notable link between EEOP and cervical osteophytes. Therefore, we strongly propose that long-term, sustained mechanical stress on the head and neck may cause EEOP.