44-year-old male with 1 month of increasing neck pain was referred for a cervical spine injection. A CT scan of the cervical spine two weeks prior (Figure A), revealed foraminal narrowing at the C5-6 level. There was a significant difference between the new scan and the previous scan. There was severe destruction of the C5-6 disc and of the adjacent C5 and C6 vertebral end plates with retrolisthesis of C5 on C6. What just happened?