Back pain after any type of spine surgery can be a symptom of late complications such as infection or problems with the hardware used to hold the spine in place. Sometimes the hardware (rods and screws) used to hold the spine in place break or get dislodged and must be repaired or removed and replaced.
The fusion might not be complete, in which case a pseudoarthrosis (a false joint) may have formed. Loss of correction or an uncorrected second spinal curve getting worse may cause back pain.
Until and unless an examination is performed, there may be no way to discern when pain is from a physical problem and what is an emotional or psychologic issue. There are many things that could cause late developing pain following spinal surgery. Don’t delay in having the surgeon take a look and figure out what’s going on.