This is the name chiropractors give to the spinal joint dysfunction that they correct by manipulation or adjustment. The subluxation is a functional entity, not necessarily a structural one, and therefore often is not visible on the X-ray.
For example, a sprained ankle is very painful and certainly causes dysfunction, but an X-ray will not usually show anything abnormal.
A modern consensus definition is: "A motion segment (a motion segment simply put is a joint, for example the joint between two vertebra) in which alignment, movement integrity, and /or physiologic function are altered although contact between the joint surfaces remains intact."
Its components are:
1.
Abnormal function and/or range of motion in a spinal joint
2. Nerve and /or vascular involvement
3.
Often, but not necessarily, some structural displacement.
Not all components have to be present, for a subluxation to exist.
Causes of subluxation are divided into two basic categories extrinsic, or external, and intrinsic, or internal. Some extrinsic causes include: Trauma, posture, occupation, micro-trauma, and overuse. Some intrinsic causes include: Fatigue, stress, scoliosis, illness, structural abnormalities, and arthritis.