I do not have any issues with my patients having chiropractic adjustments after a neck fusion that has become solid (as long as there are no other areas that demonstrate instability).
Numbness in the ulnar side of the hand could originate from new or residual cervical radiculopathy, thoracic outlet syndrome, ulnar nerve compression at the cubital tunnel (elbow) or compression at the tunnel of Guyon (wrist). A physical examination and occasionally an EMG test can determine this source of numbness.
Malalignment of the neck (torticollis) can be caused by scoliosis in the thoracic spine, antalgia (painful posturing), asymmetric degeneration of the cervical discs or malalignment from surgery. An X-ray and a physical examination will uncover the source of this problem.
Pain in the neck can be caused by the discs, facets and occasionally nerves. Many of my patients can get adjustments after ACDF surgery but that is determined on a case by case basis and it also depends upon the skill of the chiropractor.