Thank you for your question to HCM.
You are suffering from an entity called adjacent segment degeneration. Discs above and below the level of previous fusion tend to degenerate faster because of increased movement.
A disc bulge at C6-7 which does not result in cord or nerve root compression
is not likely to be the cause of your symptoms. Atlantoaxial(first and second vertebra in neck) joint degeneration occurs in elderly individuals and causes headache as well as neck pain
but is commonly underdiagnosed. A CT scan
of the cervical spine
will demonstrate this as well as show the status of bony union at previous ACDF levels as even nonunion
can cause neck pain.
Hope this is helpful. I would be happy to answer any questions you may have.