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External Occipital Protuberance

protuberantia occipitalis externa

The external occipital protuberance (inion) is the most prominent posterior midline projection of the occipital bone, approximately in the plane of the superior nuchal line. It is the attachment of the ligamentum nuchae superiorly, the trapezius muscles laterally, and the medial insertions of splenius capitis. The superior nuchal lines extend laterally from it and the greatest occipital breadth crosses at this level. It is readily palpated in the posterior midline at the junction of the neck and skull.

Region: Head & Skull

Clinical Relevance

Clinical Notes

The external occipital protuberance is the midline landmark for posterior cranial fossa skin incisions and for occipital condyle localization in posterior cervical fusion. An unusually large external occipital protuberance has been described on imaging in young adults who use mobile devices extensively (text neck), potentially representing a stress response of the nuchal ligament traction. The suboccipital approach to the posterior fossa starts at the inion and exposes the occipital bone and the posterior foramen magnum.

Pathology

Common Injuries & Conditions

Nuchal Fibrositis at Inion

Chronic traction on the ligamentum nuchae and trapezius at the external occipital protuberance from sustained forward head posture or text neck produces suboccipital bony reaction and myofascial pain, managed with posture correction, physiotherapy, and strengthening of the deep cervical flexors.