No known cause for chronic neck pain after frontal impact has been discovered yet. Scientists are studying the problem carefully. Many theories have been proposed including:
Too much strain on the ligaments leads to neck instability.
Strained ligaments can't hold the neck stable; this puts increased load on the discs.
Increased load on the discs also strains the facet joints; discs and joints start to break down under the strain.
Ligaments that are strained start to get larger or hypertrophy; the extra tissue takes up space and puts pressure on the spinal nerve roots
Unstable ligaments may set up pain signals that don't get turned off then the muscles start to react. Muscle spasm leads to pain.
These are just a few ideas of how pain from a neck injury can become chronic. The more we find out about the steps in the pain process, the better our chances will be in preventing the pain in the first place or stopping the pain once it starts.