This video explains the mechanism of chronic pain.
One thing to point out is that injury to the body does not neccessarily heal and 'go away' after 6 months as the video suggests. This is particularly so with the densely packed nerves of the spine (which sense and control movement and detect injury)
These nerves do not automatically return to normal following both the initial injury and the protracted period of inactivity which often accompanies it.
It is recommened that both the original injury (and the subsequent local scarring and joint movement dysfunctions that accompany it) AND the central brain mechanism which can enhance or 'amplify' the signal are attended to. Often this uses a combination of approaches including physically based treatements, medication and education.
Chronic pain is extremely common and often underdiagnosed.