Atlanto – occipital joint. Atlanto – axial joint.
General
- Between atlas (C1) and occipital bone.
- Connects skull with vertebral column.
Articular surfaces
- Occipital condyles (convex, on occipital bone)
- Superior articular facets of atlas (concave, kidney-shaped).
Type
- Paired synovial condylar (ellipsoid) joint.
Ligaments
- Capsule → thin, surrounds each joint.
- Anterior atlanto-occipital membrane → anterior arch of atlas ↔ anterior margin of foramen magnum.
- Posterior atlanto-occipital membrane → posterior arch of atlas ↔ posterior margin of foramen magnum.
(Both are like continuation of ligamentum flavum).
Movements
- Flexion + extension → “nodding” (yes movement).
- Lateral flexion (slight).
- Rotation → very limited (main rotation happens at atlanto-axial joint).
Clinical
- Injury here = restricted nodding; whiplash injury may stretch membranes.
Atlanto–Axial Joint (AA joint)
Connects atlas (C1) and axis (C2).
Components
There are 3 atlanto-axial joints:
- 1. Median atlanto-axial joint → between dens (odontoid process) of axis and anterior arch of atlas + transverse ligament.
- Type: Pivot synovial joint.
- 2. Two lateral atlanto-axial joints → between inferior articular facets of atlas and superior articular facets of axis.
- Type: Plane synovial joints.
Ligaments
- Capsule → surrounds each joint.
- Transverse ligament of atlas → strong band holding dens against anterior arch.
- Cruciate ligament of atlas (transverse + vertical bands).
- Alar ligaments → dens → occipital condyles, limit rotation.
- Apical ligament of dens → tip of dens → foramen magnum.
- Tectorial membrane → continuation of posterior longitudinal ligament up to occipital bone.
Movements
- Rotation (main movement) → “shaking head” (no movement).
- Atlas (and skull above) rotates around dens of axis.
- Range: ~30° to each side.