Motion mechanics: flexion, extension, minimal rotation

Physiologic range of rotation: 25°–53°

Major joint stabilizers (thickest + strongest ligaments):

• transverse lig. → allowing axial rotation
• alar ligg. → restrictors of lateral flexion, limiting excessive rotation
• joint capsules

1. INTRINSIC LIGAMENTS (= 3 layers anterior to dura mater)
   1. Odontoid ligament
      1. Apical ligament
         Function: secondary stabilizer preventing anterior shift
         Course: from middle aspect of tip of odontoid process → anterior margin of foramen magnum
      2. Alar ligaments (paired)
         Function: secondary stabilizer preventing anterior shift
         Course: from lateral aspect of tip of dens → medial aspect of occipital condyles
   2. Cruciate (cross-shaped) ligament
      1. Transverse ligament of atlas
         Function: primary stabilizer of joint preventing excessive anterior motion of atlas on axis
         Course: between medial portions of lateral masses: horizontal course behind dens
      2. Crus superioris
         Location: superior extension from transverse lig.
         Attachment: lower margin of occipital bone
      3. Crus inferioris
         Location: inferior extension from transverse lig.
         Attachment: posterior surface of body of axis
   3. Tectorial membrane
      = rostral continuation of posterior longitudinal lig.
      Course: from body of C2 → anterior margin of foramen magnum
      Function: restricts extension
2. EXTRINSIC LIGAMENTS
   = fibroelastic membranes as rostral continuations of
   1. Anterior longitudinal lig.
   2. Ligamentum flavum
   3. Nuchal ligament
      = continuation of inter- and supraspinous ligaments
      
      
      
      
      
      Course: 7^th cervical vertebra → external occipital protuberance
      Function: restriction of hyperflexion
   4. Posterior atlanto-occipital membrane
      = cephalic projection of ligamentum flavum
      Course: posterior arch of atlas → posterior margin of foramen magnum