How should i know if the spinal fusion in my back has failed?

If you had a spinal: Fusion for pain and the pain persists, that may be an indication. If you are a smoker, there is a good chance that fusion may not have occurred. A ct scan done after 12 months postop ( it can take a year for a fusion to heal) done with 2 mm axial cuts and then reconstructed in sagittal & coronal planes is the best way to image a fusion but no one study gives 100% proof of a fusion.