Joint subluxation implies a misalignment or dysfunction. It has been described as a partial dislocation but it also includes "jammed," deteriorated and damaged joints. In general, subluxated spinal facet joints are not aligned properly, don't move normally, don't receive adequate blood supply and don't transmit appropriate nerve information. Subluxations are common in the neck, more so than any other region of the spine. The main cause of neck subluxation is trauma, although poor posture, arthritis and even muscle spasm are contributing factors.
Neck subluxation usually is due to trauma. Motor vehicle accidents, sports injuries and slips and falls are the most common causes. With these forms of trauma, the neck typically experiences excessive extension and then flexion, commonly called "whiplash." The neck is susceptible to such injury because the skull acts as a 10- to 12-pound fulcrum, which puts tremendous force upon cervical spinal joints and misaligns them.
Once misaligned, subluxated joints can then effect surrounding blood flow, nerve function and muscle tension. Spinal neck joints can become completely dislocated and fractured with trauma, but subluxation is the much more common condition. Within the neck, the upper two vertebrae and the lowest two vertebrae are the most commonly subluxated because of the biomechanics of the neck and the direction the facet joints are meant to move.
Poor posture can be thought of as "micro" trauma over longer periods of time. The neck joints can be subluxated by either too much flexion, extension or rotation. Sitting at a desk or work station often creates too much flexion for too long, which causes the natural curvature of the neck to reverse and force the upper two neck joints into unnatural positions, called an atlantoaxial subluxation. Sleeping prone, or face down, often creates too much rotation for too long, which causes excessive torsion among the highest vertebra and the skull, called a suboccipital subluxation.
Both osteoarthritis--the "wear and tear" type--and rheumatoid arthritis--the auto-immune / inflammatory type--cause spinal joint destruction. Joint destruction, such as bone spurs and disc degeneration, invariably cause misalignments and dysfunction. Neck joint subluxations created from mild to moderate arthritis can become unstable with movement, although severe arthritis often leads to fusion.
Muscle tension, which can lead to spasm, caused by either continual mental stress or physical exertion also contributes to neck subluxation because the muscles can clamp down on the spinal joints, causing malposition and restriction of movement. A common neck muscle that can become spasmodic due to stress, exertion or even a chill is the sternocleidomastoid muscle. When this muscle spasms, it's called an acute torticollis.