How do i tell if spine fusion will work?

Fusion confusion: There are many reasons a spine fusion can be recommended. For back pain, a fusion should only be considered as a last resort after all other options (PT, injections: facet joint, sacroiliac joint) have been performed and no relief has been achieved. If you have slippage of a vertebrae (spondylolisthesis) or have fractured a vertebrae and the spine is unstable then fusion may be the best option.

Depends, but not: Normally. If you have instability, then yes. However, if it is just to treat pain, you will most likely just trade the pain for another level. Only do it if you have tried all other medications and therapies.