The jaw joint (temporomandibular joint) begins to breakdown when the stresses overcome the tissue ability to function and repair. Usually this involves some type of trauma. This can be micro-trauma or macro-trauma. Micro-trauma by itself does not cause damage, but if repeated enough over time does cause tissue damage. Drumming your fingers on a table does not cause damage, but if done for hours without stopping it can cause an injury. Given enough time, the structures cannot withstand the forces generated and the tissues breakdown and become unable to function adequately. Macro-trauma is usually caused by one incident of such magnitude that it can damage the tissue beyond normal repair capabilities. Smashing your finger with a hammer could be an example of macro-trauma.
In the diagram at the right we observe some of the muscles that help move and support the jaw movements. An injury to the joint would cause these muscles to compensate and this increased function (muscle splinting) can cause knots or a Charlie horse, now termed a trigger point. Trigger points are painful at the source and can also refer pain to other structures and are the primary cause for most patients head and neck pain.