People with craniocervical instability (CCI) or atlantoaxial instability (AAI) sometimes wear a cervical collar to limit head and neck movement when the ligaments that stabilize the upper spine are weak or injured. The collar helps by reducing strain on those ligaments, easing pressure on the brainstem and nerves, and often lessening symptoms like headache, dizziness, or neck pain. It can also be used diagnostically — if symptoms improve while wearing it, that suggests instab