Flexion Dysfunction of Atlanto-Occipital Joint Associated with Cervical Spondylosis.

Stiff O-C1 , which is defined as FOC ≤ 4.2°, represented decreased flexion dysfunction of atlanto-occipital joint and is closely associated with high risk for the occurrence of CS. This finding could show a possible relationship between upper and lower cervical spine and help spine surgeons to understand the pathological process of CS and implement appropriate management.