Can you tell me how to know if my spinal fusion has failed?

Fusion failure: There are a number of ways a spinal fusion may fail. If the hardware breaks and the vertebrae can move - this can be detected by a special Xray called a flexion-extension Xray, failure of bony fusion is best detected with a CAT scan to look for bone formation. Sometimes pain persists, but all studies show bone has formed and hardware is in good position, in which case the fusion has not failed.