I was recently in a car accident that totaled out my vehicle.  I was able to walk away from it but did not feel the need for medical attention at that time.  Hours later, my lower back was is terrible pain.  I was x rayed and determined nothing was broken, but the x ray shows that I have a partial fusing on the left side of my 5th vertebrae.  Could this be a cause for my pain?
I read your question and I understand your concern. Generally speaking vertebral fusion is a predisposing factor for back pain because the limited mobility between the fused vertebrae means more strain to other vertebral levels which do suffer degenerative changes in time.However, it would be a gradual process due to vertebral change with the passing of the years, so if it started acutely only after the accident then it is not the only cause. Although no visible fracture, other supportive components of the spine such joints, ligaments, muscles have been affected by the accident but don't need specific treatment apart from painkillers and muscle relaxants and hopefully will gradually heal in time. I hope to have been of help.