Subluxation
According to Upper cervical chiropractic, a subluxation can only occur in upper cervical vertebrae. A subluxation must have the following components:
1. A vertebra out of alignment with its co-respondents above and below.
2. Occlusion of a foramen or foramina
3. Pressure upon nerves
4. Interference with transmission of the normal quality flow of mental impulse supply between brain and body
5. No vertebrae is subluxated unless it is off normal position in three directions and remains such (Vol. XVIII)
Read more about this topic: Upper Cervical Specific Chiropractic