Inmaximum extension,theregion ofthe atlantooccipital jointislocked and rotation largelytakesplace in the lower segmentsof the cervical spine and in the cervicothoracic junction. Restricted mobility with pain isa sign of segmentaldysfunction.The mostlikely causes include degenerative changes in the middle and lower cervical spine (spondylosis, spondylarthritis, or uncovertebral arthritis). Vertigo suggests compromised vascular supply from the vertebral artery.