Abnormality of the cervical spine Cervical spine instability 2010-02-23T11:15:32Z UMLS:C0410652 HP:0010646 The cervical spine is made up of two anatomically and functionally distinct segments: the upper cervical spine (C1and C2), which possesses the most rotational mobility with some degrees of frontal and sagittal plane mobility, and the lower cervical spine, which allows for two types of movements - flexion-extension and inclination-rotation. Cervical instability mainly involves the upper cervical spine, particularly between C1 and C2. Craniocervical ligaments are the main determinants of cervical spine stability. SNOMEDCT_US:202821008 An abnormal lack of stability of the cervical spine.