The term "pseud" means false and "arthrosis" refers to joint. The term "pseudarthrosis" then means false joint. A surgeon uses this term to describe either a fractured bone that has not healed or an attempted fusion that has not been successful. A pseudarthrosis usually means that there is motion between the two bones that should be healed (or fused together).
There is usually continued pain when the vertebrae involved in a surgical fusion do not heal. The pain may increase over time. The spinal motion can also stress the metal hardware used to hold the fusion-possibly causing them to break. You may need additional surgery for a pseudarthrosis. Your surgeon might want to add more bone graft, replace the metal hardware, or add an electrical stimulator to try to get the fusion to heal.