An adjustment is one of the main tools chiropractors use to correct joint mechanics. A joint by definition is a moveable articulation between two bones. Each joint has a normal range of motion.

An adjustment (manipulation) is used after a careful assessment to restore normal joint movement. Often massage, stretching or other techniques are used to relax the surrounding musculature first.

In the adjustment the person is positioned to stretch the joint apart gently. While the person tries to relax the musculature a brisk and specific thrust is applied by hand to the joint, opening it to its normal physiological range. Often a popping sound is heard or felt as the dissolved gasses in the joint form a bubble.

The effect of the adjustment is to lower the tone of the guarding reflex. A sore or dysfunctioning joint will be reflexly guarded by the body (sensory nerves in and around the joint trigger muscle contraction). Gapping the joint open reduces the over-stimulation to those sensory nerves, suppressing the reflex.

The benefits are multiple:

• impingement (pinching) of the joint is reduced, relieving pain and irritation.
• normal mechanical movement is restored to related neighbouring joints, muscles and connective tissues which had been compensating for the restricted joint.
• local endorphin release can be stimulated numbing pain.
• local circulation and joint nutrition is improved due to the reduced tension and pressures.
• likewise lymphatic drainage can be improved locally.
• in some situations direct pressure on a nerve root exiting the spine (causing sciatica or arm pain) can be relieved.
• reduced joint irritation can reduce nervous system over-stimulation locally, which has been shown to have effects on the autonomic nervous system tone (which controls the automatic functions of the body). Though this reflex effect on visceral organs is quite weak, it is present.  In the grand scheme of the body, though, it is a very small player.

While the specific effect of an adjustment on the joint may be relatively local, if done correctly (ie to the right joint in the right way) the overall effects can be profound, affecting other related joints, muscles and ligaments mechanically (picture a bicycle chain with one frozen link that keeps popping the chain off the sprocket). It is the skill of the chiropractor in identifying the problem and then adeptly performing the required adjustments that dictate the success of the treatment.