Anatomy, Head and Neck, Suboccipital Muscles


Introduction

The suboccipital muscles are a group of four muscles located inferior to the occipital bone. These four muscles include the rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis superior, and obliquus capitis inferior. The muscles serve as postural support and allow extension and rotation movements of the neck. The muscles are innervated by the suboccipital nerve, which is formed by the dorsal ramus of C1. Three of the four muscles form the suboccipital triangle, a common anatomic landmark that localizes the vertebral artery and suboccipital nerve. This landmark is of particular importance to surgeons who operate in the posterior cervical region to avoid life-threatening bleeding.

The vertebral artery travels a torturous course behind the suboccipital muscles while giving off branches that supply the suboccipital muscles. Clinically, the suboccipital muscles have importance regarding their close relationship to the vertebral artery and surgical access to the posterior cranial fossa. Various cranial pathologies can be accessed by a suboccipital surgical approach that requires knowledge of the posterior cervical region. The group of four muscles has been implicated in the pathogenesis of cervicogenic headaches due to their connections with the dura mater.

Structure and Function

The suboccipital muscles are a group of four muscles located inferior to the external occipital prominence of the skull. The four muscles include the rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis inferior, and obliquus capitis superior.[1] 

Directly posterior (or superficial) to the suboccipital muscles is the semispinalis capitis. Further posterior to these muscles includes the splenius, sternocleidomastoid, and trapezius. Three of the four suboccipital muscles form an anatomic triangle labeled the suboccipital triangle. The obliquus capitis superior superolaterally forms the triangle's borders, rectus capitis posterior major superomedially, and the rectus capitis inferiorly. Within this triangle, the suboccipital nerve and vertebral artery can be found. While the suboccipital muscles function as postural muscles, they also allow for movement of the head.[1][2]

Embryology

The suboccipital muscles, similar to all striated and smooth muscle, is derived from the mesoderm. With attachments to the base of the skull, there is a complex interaction between the mesoderm and the occipital sclerotomes that form the occipital bone. During embryologic development, derangements can occur that lead to anatomic variations with the suboccipital muscles.[3][4][5][6]

Blood Supply and Lymphatics

The suboccipital muscles cover the vertebral artery as it enters the transverse process of C1. The vertebral artery is divided into four segments, which are separated based on anatomical positioning within the body. The portion of the vertebral artery behind the suboccipital muscles is labeled the third segment (V3). V3, or the suboccipital segment, travels from the transverse process of C2 through the transverse process of C1 and into the dura mater. During this course, the V3 segment gives off a muscular artery that supplies the suboccipital muscles.

The main venous structure surrounding and draining the suboccipital muscles is the suboccipital venous plexus. These surrounding veins are located posterior to the suboccipital muscles and anastomose with a venous sinus that surrounds the V3 segment of the vertebral artery.[7] 

Nerves

The suboccipital muscles are innervated by the suboccipital nerve, which arises from the dorsal rami of C1. Before the formation of the rami, rootlets emerge from the spinal cord at the level of C1. Ventral and dorsal rootlets combine to form ventral and dorsal rami. The dorsal or posterior ramus exits through the posterior atlanto-occipital membrane before branching off into different segments to innervate the suboccipital muscles and the semispinalis capitis.[7][8]

Muscles

Suboccipital Muscles

  • Rectus capitis posterior major
  • Rectus capitis posterior minor
  • Obliquus capitis superior
  • Obliquus capitis inferior

Rectus Capitis Posterior Major

  • Origin: Spinous process of C2 vertebrae
  • Insertion: Inferior nuchal line of the occipital bone
  • Action: Extension of the neck, ipsilateral rotation of the head

Rectus Capitis Posterior Minor

  • Origin: Posterior tubercle of C1 vertebrae
  • Insertion: Inferior nuchal line of the occipital bone
  • Action: Extension of the neck, ipsilateral rotation of the head

Obliquus Capitis Superior

  • Origin: Transverse process of C1 vertebrae
  • Insertion: Portion of the occipital bone between nuchal lines
  • Action: Extension and lateral flexion

Obliquus Capitis Inferior

  • Origin: Posterior tubercle of C2 vertebrae
  • Insertion: Transverse process of C1 vertebrae
  • Action: Ipsilateral rotation of the head

Suboccipital Triangle

  • The suboccipital triangle is an anatomic landmark involving the suboccipital muscles and allows for the localization of the vertebral artery and the suboccipital nerve.
  • Rectus capitis posterior major forms the superomedial border
  • Obliquus capitis superior forms the superolateral border
  • Obliquus capitis inferior forms the inferolateral border
  • The posterior atlanto-occipital membrane forms the floor of the triangle
  • The roof of the triangle is formed by the semispinalis capitis muscle[2][9]

Physiologic Variants

There have been case reports that have found variants of the suboccipital muscles. The presence of a third rectus capitis muscle was found in the suboccipital region in one patient.[5] In another instance, there was a unilateral absence of rectus capitis posterior minor muscle replaced with two rectus capitis posterior major muscles.[6] Both of these variants may provide further insight and explanations for the development of cervicogenic headaches.

Surgical Considerations

When considering surgery for various diseases involving the cerebellum, spinal cord, or atlantoaxial joint, a posterior suboccipital approach may be used. Understanding the relationship between neurovascular structures within the suboccipital region is crucial before surgery to avoid life-threatening injury. The suboccipital muscles form a suboccipital triangle, which can be used as a consistent marker for the location of the vertebral artery and suboccipital nerve.

The suboccipital triangle is outlined by the rectus capitis posterior major, obliquus capitis superior, and obliquus capitis superior. The third portion of the vertebral artery courses horizontally as it moves throughout the suboccipital triangle. Additional landmarks that can be utilized during a posterior surgical approach include the spinous process of C2, the posterior arch of C1, and the transverse processes of C1/C2.[10] The suboccipital approach has been used for multiple neurologic and vascular pathologies.[11][12] 

Clinical Significance

The suboccipital muscles form an anatomic landmark of particular importance to surgeons operating within the posterior cervical spine or posterior cranial fossa region. The suboccipital triangle forms a distinct area where surgeons can be aware of the vertebral artery and position within the posterior cervical region. The close relationship between the suboccipital muscles and the vertebral artery may be relevant in patients with significant atherosclerosis. Contraction of the suboccipital muscles may lead to minor compression of the artery, which further reduces blood flow. The decreased blood flow can lead to symptoms of light-headedness and dizziness. Additionally, the suboccipital muscles can be strained by constant movement or injury. This may lead to headache or neck pain that can be relieved through physical therapy and pain control.

Cervicogenic Headaches

Cervicogenic headaches initially present as unilateral neck pain and spread to the head. The pain becomes worse with movement or palpation of the neck. This type of headache can commonly be mistaken for a migraine or tension headache. The pain may radiate to other areas, including the shoulder and arm. The suboccipital muscles have been investigated as a potential cause of cervicogenic headaches. In one study, the suboccipital muscles were found to have increased tone and stiffness compared to healthy controls.[13] The suboccipital muscles have been noted to have connections with the dura mater; a connection labeled the “myodural bridge.” It has been hypothesized that tension produced by the suboccipital muscles may directly lead to tension within the dura leading to characteristic cervicogenic headache pain.[14] 

Other studies have implicated the C1-C3 nerves as potential causes of a cervicogenic headache.[15] Treatment of these headaches involves physical therapy. If symptoms persist, other therapies include steroid injections for severe symptoms.



(Click Image to Enlarge)
Suboccipital triangle, Multifidus, Thoracic vertebra, First and Second Rib, Semispinalis capitis, Longissimus capitis, Oblique Superior and Inferior, Rectus Posterior Minor
Suboccipital triangle, Multifidus, Thoracic vertebra, First and Second Rib, Semispinalis capitis, Longissimus capitis, Oblique Superior and Inferior, Rectus Posterior Minor
Contributed by Wikimedia Commons,"Medical gallery of Mikael Häggström 2014" (Public Domain)

(Click Image to Enlarge)
Suboccipital Nerve, Greater occipital nerve, Cutaneous branch suboccipital nerve, Lesser occipital nerve, Third occipital nerve
Suboccipital Nerve, Greater occipital nerve, Cutaneous branch suboccipital nerve, Lesser occipital nerve, Third occipital nerve
Illustration by Emma Gregory
Article Details

Article Author

Tom George

Article Editor:

Prasanna Tadi

Updated:

10/14/2021 7:33:47 AM

References

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