You need to mention your age and sex. Also the level at which disc replacement was done.
is the sort of sack that contains the nerves at the back. Some amount of distortion can be there with aging but it is only the degree ( after seeing the films) that matters. This distorsion can also be due to disc degeneration which you seem to be prone of seeing your previos history.
Also a fusion at one level, increases stress
at adjacent levels.
This can be the reason for your pain. Try some analgesics, rest for a few days. If it does not work, see your doctor, who will then reviw your MRI
and x ray
and then advice you appropriately.