Was there any sort of whiplash type injury from the accident?

Any pain or symptoms in hands or arms or neck?

Soft tissue injuries don't show up on MRIs or many imaging tests at all.
A very advanced PT should be able to assess if it may be soft tissue vs spine problems.

If you have a copy of the MRI on disk or films you could take them somewhere else to be evaluated independently.
Even an experienced/expert chiro could do an assessment w/ no adjusting.