atlanto-occipital joint

The atlanto-occipital joint is an articulation between the atlas bone and the occipital bone. It consists of a pair of condyloid joints. It is a synovial joint.

The ligaments connecting the bones are:

• Two articular capsules
• Posterior atlanto-occipital membrane
• Anterior atlanto-occipital membrane

The capsules of the atlantooccipital articulation surround the condyles of the occipital bone, and connect them with the articular processes of the atlas: they are thin and loose.

Atlantooccipital fusion, also known as occipitalization of the atlas, is a congenital or acquired anomaly characterized by the partial or complete fusion of the atlas to the base of the occipital bone. It is found in 0.12% to 0.72% of the population.{{Cite journal |last1=Sharma |first1=D. K. |last2=Sharma |first2=Deepak |last3=Sharma |first3=Vandana |date=June 2017 |title=Atlantooccipital Fusion: Prevalence and its Developmental and Clinical Correlation |journal=Journal of Clinical and Diagnostic Research |volume=11 |issue=6 |pages=AC01–AC03 |doi=10.7860/JCDR/2017/26183.9999 |issn=2249-782X |pmc=5535332 |pmid=28764139}} This fusion results in the elimination or reduction of movement and abnormal neck posture, or even narrowing of the foramen magnum compressing the spinal cord.{{Cite journal |last1=Davis |first1=Bibin Joe |last2=Chaudhary |first2=Dinesh Chander |last3=Jayan |first3=Balakrishnan |last4=Thakur |first4=Vivek Kumar |last5=Chopra |first5=Sukhbir Singh |last6=Sandhu |first6=Guramrit |date=2024-04-01 |title=Atlanto-occipital Assimilation an Incidental Cephalometric Finding: Diagnosis and Clinical Implications – A Case Report |journal=Journal of Indian Orthodontic Society |language=EN |volume=58 |issue=2 |pages=199–204 |doi=10.1177/03015742241231653 |issn=0301-5742|doi-access=free }}

The movements permitted in this joint are:

• (a) flexion and extension around the mediolateral axis, which give rise to the ordinary forward and backward nodding of the head.
• (b) slight lateral motion, lateroflexion, to one or other side around the anteroposterior axis.

Flexion is produced mainly by the action of the longi capitis and recti capitis anteriores; extension by the recti capitis posteriores major and minor, the obliquus capitis superior, the semispinalis capitis, splenius capitis, sternocleidomastoideus, and upper fibers of the trapezius.

The recti laterales are concerned in the lateral movement, assisted by the trapezius, splenius capitis, semispinalis capitis, and the sternocleidomastoideus of the same side, all acting together.

The atlanto-occipital joint may be dislocated, especially from violent accidents such as traffic collisions.{{cite journal |last1=Govender |first1=S. |last2=Vlok |first2=G. J. |last3=Fisher-Jeffes |first3=N. |last4=Du Preez |first4=C. P. |title=Traumatic dislocation of the atlanto-occipital joint |journal=The Journal of Bone and Joint Surgery. British Volume |date=August 2003 |volume=85-B |issue=6 |pages=875–878 |doi=10.1302/0301-620X.85B6.14092 }} This may be diagnosed using CT scans or magnetic resonance imaging of the head and neck. Surgery may be used to fix the joint and any associated bone fractures. Neck movement may be reduced long after this injury. Such injuries may also lead to hypermobility, which may be diagnosed with radiographs.{{cite journal |last1=Wiesel |first1=Samuel |last2=Kraus |first2=David |last3=Rothman |first3=Richard H. |title=Atlanto-occipital Hypermobility |journal=Orthopedic Clinics of North America |date=October 1978 |volume=9 |issue=4 |pages=969–972 |doi=10.1016/S0030-5898(20)32207-0 |pmid=740387 }} This is especially true if traction is used during treatment.

File:Gray129.png|Occipital bone. Outer surface.

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Category:Joints

Category:Joints of the head and neck