Atlanto-occipital joint
Original Editor - Rachael Lowe
Lead Editors - Evan Thomas
Description
The atlanto-occipital joint also known as the C0-C1 is a paired symmetrical articulation between the cervical spine and the base of the skull[1]. It includes the occipital condyle and the superior articular surfaces of the first cervical vertebra (C1 or Atlas), allowing flexion, extension and lateral tilt of the head[2]. Along with the atlantoaxial joint, it makes up a group called the craniovertebral joints.
Articulating Surfaces
Occipital condyles and a superior articular facets of the atlas[1].
Ligaments & Joint Capsule
The ligamentum nuchae (LN) is a continuation of the supraspinous ligament, which spans from the occipital protuberance to the vertebra prominens (C7).The atlanto-occipital joint (AOJ) is an important transitional region, which supports and stabilizes the cranium to the spine with its surrounding ligamentous structures. An injury to this joint is often accompanied by brain injury and may be fatal. A good understanding of the anatomy of this joint is required to timely diagnose an AOJ instability and intervene via the means of an immediate fixation. We discuss the normal anatomy of and anatomical variations within the occipito-atlantoaxial complex, the classification systems to describe its disruption, and its clinical significance. limits excessive neck flexion.[5] The alar ligament (AL) (Figure 6) limits axial rotation and lateral flexion, stabilizing the AOJ. The AL is the primary ligament for the stabilization of the joint when the transverse ligament is damaged.[5] The AL also anchors the dens to the OCs and is very tough.[6] The anterior and posterior atlanto-occipital membranes attach to their respective surfaces on the atlas and the foramen magnum.[5] The apical ligament (Figure 6) joins the tip of the odontoid process to the basion (the most anterior point of the foramen magnum in the median sagittal plane) and has no mechanical role and is absent in 20% of the bodies studied by Tubbs et al.[5] The AOJ allows 11–13° of freedom, allowing for 25° of flexion and extension, 5° of axial rotation, and combined motions.[7] Flexion is limited by the contact between the forame n magnum and the dens.[7]
The capsule is rather roomy and relaxed and the joint possesses no individual accessory ligaments. Stability is provided by:
- Two articular capsules
- Posterior atlanto-occipital ligament
- Anterior atlanto-occipital ligament
Degrees of Freedom
Two degrees of freedom are available at this joint:[3]
- Flexion/extension
- Lateral flexion/conjunct rotation
Osteokinematics[3]
- Flexion/extension
- Cardinal (pure) swing
- Total ROM: 30° (10° flexion, 20° extension)
- Axis: Transverse axis through external auditory meatus
- Lateral flexion
- Arcuate (impure) swing with coronal conjunct rotation (e.g. right lateral flexion occurs with conjunct left rotation)
- Total ROM: 15° (8-10° in each direction)
- Axis: Oblique sagittal axis through the nose (approximately)
- Associated with AA joint rotation
- Rotation (conjunct)
- Occurs with lateral flexion due to the slanted articular surfaces, anteromedial orientation of the articular facets, and the alar ligaments
- Total ROM: 5-7° in each direction
- Axis: Vertical axis anterior to the foramen magnum
Arthrokinemtics[3]
- Flexion
- Forward tilt/nod of the head
- Posterior glide of the convex occipital condyles on the concave atlantal facets
- Atlas moves anterior and cranially
- Dens follows atlas and approaches the clivus
- Occiput and the posterior atlantal arch separate
- Extension
- Backward tilt of the head
- Anterior glide of the convex occipital condyles on the concave atlantal facets
- Lateral flexion (left lateral flexion example provided below)
- Left lateral tilt of the head causes a contralateral glide of the occiput
- Conjunct right rotation occurs due to the anteriormedial axis of the joint surfaces
- Right glide of the occipital condyles causes relative anterior glide of the left condyle on and a relative posterior glide of the right condyle
- Occipital portion of the right alar ligament tightens, with the left being slackened
- Tension in the right alar ligament pulls on the dens and causes a left rotation of the axis
- Spinous process of the axis moves to the right creating a relative right rotation of the AA joint
Function Of The Muscles surrounding the Atlanto-Occipital Joint
Flexion is produced mainly by the action of the rectus capitis anterior. Limited by tectoral membrane.
Extension by the rectus capitis posterior major and minor, assisted by the obliqus capitis superior, the semispinalis capitis, splenius capitis, sternocleidomastoid, and upper fibers of the trapezius.
The rectus capitis lateralis are concerned in the lateral flexion, assisted by the trapezius, splenius capitis, semispinalis capitis, and the sternocleidomastoid of the same side, all acting together.
Pathology
- Jefferson fracture
- Atlanto-occiptal dislocation
Resources
References
- ↑ 1.0 1.1 Bodon G, Choi PJ, Iwanaga J, Tubbs RS. The atlanto-occipital joint: a concise review of its anatomy and injury. Anatomy. 2017;11(3):141-5.
- ↑ Da Cruz LB, Faleiros MC, Guimarães HM, Sugino RL, de Carvalho CA, Barbosa MM, Verri ED. Atlanto-occipital fusion: Case report. Research, Society and Development. 2023 Dec 21;12(14):e83121444513-
- ↑ 3.0 3.1 3.2 Orthopaedic Division of the Canadian Physiotherapy Association. Biomechanics of the Atlanto-Occipital Joint. Clinical Technique Manual: Level II Upper Quadrant (2010). Pg 28-30.