The splenius capitis is a broad, strap-like muscle on the posterolateral neck running obliquely from the lower cervical and upper thoracic spinous processes to the mastoid process and occipital bone. Its oblique fibre direction allows it to perform both rotation and lateral flexion to the same side when acting unilaterally, and bilateral contraction produces head and neck extension. It is one of the primary muscles involved in headache and cervical pain syndromes.
| Origin | Lower half of the nuchal ligament and spinous processes of C7 through T3 or T4 |
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| Insertion | Mastoid process of the temporal bone and lateral aspect of the superior nuchal line of the occiput |
| Nerve Supply | Posterior rami of the middle cervical nerves (C3, C4) |
| Blood Supply | Occipital artery |
| Actions | Extension of the head and neck; Ipsilateral lateral flexion of the head; Ipsilateral rotation of the head; Acts bilaterally to extend the head and upper neck |
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Its diagonal attachment from lower cervical and upper thoracic spine to the skull base makes it an efficient head extensor and rotator that activates strongly during any head-turning task involving speed or resistance, such as checking blind spots while driving.
Splenius capitis trigger points are a major contributor to cervicogenic headache, referring pain from the posterior neck through the head to the vertex and occasionally to the eye. The suboccipital triangle, deep to the splenius capitis, contains the greater occipital nerve, and splenius capitis tightness can indirectly compress this nerve and contribute to occipital neuralgia. Whiplash injuries predictably injure the splenius capitis and its synergists.
The splenius capitis is palpable as a broad band on the posterolateral neck running from just medial to the mastoid process obliquely toward the lower cervical spine, becoming firm during resisted head extension and ipsilateral rotation.
Acute muscle tear from sudden forced neck flexion or rotation such as in a whiplash injury, producing posterolateral neck pain with restricted rotation that is reproduced by resisted head extension and ipsilateral rotation.
Referred pain from splenius capitis trigger points producing a headache pattern from the posterior neck radiating over the head to the vertex, managed with trigger point release, manual therapy, and postural correction.
