Occipitoatlanto Joint (OAJ)
Atlanto-occipital joint, C0-C1 Joint
Overview
The Occipitoatlanto joint (OAJ) refers to the articulation between the superior occiput (C0) and the inferior Atlas (C1). Specifically, between the occipital condyles and the Atlas’ superior lateral massees1.
The atlanto-occipital joints provide independent movement of the cranium relative to the atlas (C1)2.
The head and atlas (C1) create a 1st-class lever with the fulcrum at the occipital condyles1. The center of gravity (external force) centers above the TMJ1. The posterior neck muscles create an internal force to counteract gravity1.
Anatomy
The joints are formed by the protruding convex condyles of the occipital bone fitting into the reciprocally concave superior articular facets of the atlas2.
Joint Capsule
The joint capsules are “roomy”1 and support the symmetrical synovial joints1.
Stability
Structural stability
The convex-concave relationship provides inherent structural stability to the articulation2.
Anteriorly, the capsule of each atlanto-occipital joint blends with the anterior atlanto-occipital membrane (Fig. 9.41). Posteriorly, the capsule is covered by a thin, broad posterior atlantooccipital membrane (Fig. 9.42). As depicted on the right side of Fig. 9.42, the vertebral artery pierces the posterior atlanto-occipital membrane to enter the foramen magnum. This crucial artery supplies blood to the brain.
The concave-convex structure of the atlanto-occipital joints permits angular rotation primarily in two degrees of freedom. The primary motions are flexion and extension. Lateral flexion is slight. Axial rotation is very limited and usually not considered as the third degree of freedom.
Flexion-Extension
Flexion and extension of the OAJ occur in the sagittal plane.
Dysfunction
Superficial Back Line (SBL) is associated with postural dysfunctions, including anterior shift or rotation of the occiput (C0) on C13.