Hello sir You have a valid question to which I want to answer with a simple illustration our spine is like a snake it is flexible and can bend to a great extend. What spinal fusion surgery does is it makes two units into one so they ease the pain , but what it also does it makes the back stiff,so now the load on the adjacent vertebra is more on bending. The drawback is now the spine has lost its flexibility. Earlier in the spine were 33 units each unit contributing to the flexibility now after fusion surgery at one level renders two vertebrae into one unit so now only 32 vertebrae can bend. It also increases the load on the vertebrae level one above and one below the fused vertebra. So in long run they also we d start paining, which has started now with u what u need to do now is take care of your back, avoid straining it. Take your doctors opinion and get an Mri done to see the status of disc prolapse on adjacent vertebra and get treated appropriately