The obliquus capitis inferior is the largest of the four suboccipital muscles and the only one that does not attach to the skull. It runs laterally and slightly superiorly from the spinous process of the axis to the transverse process of the atlas, forming the inferomedial boundary of the suboccipital triangle. It is the primary muscle responsible for rotating the head on the neck at the atlantoaxial joint, accounting for approximately 50% of total cervical axial rotation.
| Origin | Spinous process and posterior surface of the lamina of the axis (C2) |
|---|---|
| Insertion | Posterior surface of the transverse process of the atlas (C1) |
| Nerve Supply | Suboccipital nerve (posterior ramus of C1) |
| Blood Supply | Vertebral artery; Occipital artery |
| Actions | Ipsilateral rotation of the atlas on the axis (rotates the head to the same side) |
|---|
The greater occipital nerve (C2 dorsal ramus) passes through or around the obliquus capitis inferior as it courses superiorly toward the scalp. Hypertrophy or spasm of the obliquus capitis inferior can entrap the greater occipital nerve, producing occipital neuralgia characterised by shooting pain from the suboccipital region to the vertex, with a positive Tinel sign at the nerve's exit medial to the muscle. Dry needling of the obliquus capitis inferior is among the most effective interventions for cervicogenic occipital headache and greater occipital neuralgia.
Palpated in the deep suboccipital groove between the C2 spinous process medially and the posterior C1 transverse process laterally. With the patient prone and the head rotated slightly away, sustained pressure directed toward the C2 spinous process will engage the muscle belly.
Spasm or hypertrophy of the obliquus capitis inferior compresses the greater occipital nerve as it passes around the inferior border of the muscle, producing occipital neuralgia with shooting pain from the suboccipital region to the vertex, managed with suboccipital muscle release, greater occipital nerve block, or neurostimulation.
Inflammatory or traumatic injury to the atlantoaxial complex with associated obliquus capitis inferior dysfunction produces rotational torticollis with pain and restricted head rotation, visible on open-mouth CT as persistent asymmetric atlantoaxial rotation.
