What Kind of Joint Is the Atlanto-Axial Joint?

Written by erica krimmel
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What Kind of Joint Is the Atlanto-Axial Joint?
The atlanto-axial joint is between the first two vertabrae and allows lateral motion of the head. (Stockbyte/Stockbyte/Getty Images)

The atlanto-axial joint occurs between the atlas and the axis bones, which are the first two cervical vertebrae of the spine. It is a compound synovial joint; that is, it moves freely and is composed of multiple bone articulations. A layer of cartilage, as well as lubricating synovial fluid, facilitates this movement.

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Median Atlanto-Axial Joint

Three primary bone articulations comprise the atlanto-axial joint; the median atlanto-axial joint is one of them. This is a pivot joint between dens -- also known as the orthontoid process -- of the axis and anterior arch of the atlas. The position of the dens is maintained by the transverse ligaments of the axis. Another pair of alar ligaments attach the dens to the occipital condyle of the rear skull, preventing over-rotation within the atlanto-axial joint.

Lateral Atlanto-Axial Joints

Two lateral atlanto-axial joints complement the median atlanto-axial joint. On each of these, the inferior articulate facet of atlas pivots on the superior articulate facet of axis. The concave shape of the atlas perfectly cups the convex axis, and loose, capsular ligaments allow back and forth gliding during the rotation of the atlas. Additionally, the lateral atlanto-axial joints help to transfer the weight of the skull from the atlanto-occipital joint.

Movement

The atlanto-axial joint is called the joint of "no" or "negative expression" because that is the motion it allows the head to make. The dens of the axis is the fixed pivot, while the anterior arch and transverse ligaments of the atlas form a rotating ring. As the atlas pivots around the dens, carrying with it the mass of the skull, it also lowers slightly. Alar ligaments connect the dens to the skull and prevent over-rotation.

Muscles

The obliquus capitis inferior, splenius capitis and rectus capitis posterior major muscles of one side of the bodywork in tandem with the sternocleidomastoid of the other side to control motion of the atlanto-axial joint. Along with the alar ligaments, these muscles also prevent over-rotation of the joint.

Other Synovial Joints

The majority of joints in the human body are synovial, just like the atlanto-axial joint. Synovial joints are classified by the type of motion they allow; ball and socket, hinge, gliding and pivot are the primary categories. In addition to the atlanto-axial, another common pivot joint is the radioulnar joint of the forearm.

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