The suboccipital triangle contains the horizontal part of the vertebral artery before it pierces the posterior atlantooccipital membrane and enters the subarachnoid space. The triangle is composed of muscles that maintain the posture of the head on the neck and move the head at the atlantooccipital and atlantoaxial joints. These muscles should be considered in the diagnosis of postural problems such as torticollis and the testing of neurological function after a cerebrovascular accident (13).
The suboccipital triangle lies deep to the trapezius and semispinalis capitis muscles. Three muscles form the suboccipital triangle and a fourth is associated with the triangle. All these muscles act to extend the head at the atlantooccipital joint or rotate the head at the atlantoaxial joint. The rectus capitis posterior major is attached to the bifid spinous process of the axis and runs superiorly to insert into the inferior nuchal line. The inferior oblique muscle attaches to the spine of the axis, lateral to the attachment of the rectus major, and inserts on the transverse process of the atlas. The superior oblique muscle attaches on the transverse process of the atlas and inserts superiorly between the superior and inferior nuchal lines. These three muscles define the suboccipital triangle. Medial to the triangle on each side is the rectus capitis posterior minor muscle, which is attached to the posterior tubercle of the atlas and inserts on the medial part of inferior nuchal line. All four muscles receive motor innervation from the posterior primary ramus of C1, the suboccipital nerve.
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