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The atlanto-axial joint is a joint in the upper part of the neck between the atlas bone and the axis bone, which are the first and second cervical vertebrae. It is a pivot joint . Structure
In animal anatomy, a pivot joint (trochoid joint, rotary joint or lateral ginglymus) is a type of synovial joint whose movement axis is parallel to the long axis of the proximal bone, which typically has a convex articular surface.
The atlanto-occipital joint allows the head to nod up and down on the vertebral column. The dens acts as a pivot that allows the atlas and attached head to rotate on the axis, side to side. The atlas's chief peculiarity is that it has no body, [3] which has fused with the next vertebra. [4]
The joint space equals the distance between the involved bones of the joint. A joint space narrowing is a sign of either (or both) osteoarthritis and inflammatory degeneration. [12] The normal joint space is at least 2 mm in the hip (at the superior acetabulum), [13] at least 3 mm in the knee, [14] and 4–5 mm in the shoulder joint. [15]
The atlanto-occipital joint may be dislocated, especially from violent accidents such as traffic collisions. [1] This may be diagnosed using CT scans or magnetic resonance imaging of the head and neck. [1] Surgery may be used to fix the joint and any associated bone fractures. [1] Neck movement may be reduced long after this injury. [1]
Joints can also be classified based on their anatomy or on their biomechanical properties. According to the anatomic classification, joints are subdivided into simple and compound, depending on the number of bones involved, and into complex and combination joints: [19] Simple joint: two articulation surfaces (e.g. shoulder joint, hip joint)
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The internal structure of the odontoid process is more compact than that of the body. The odontoid peg is the ascension of the atlas fused to the ascension of the axis. The peg has an articular facet at its front and forms part of a joint with the anterior arch of the atlas. It is a non-weight bearing joint.