Hello, i have ankylosing spondylitis and had "new l3/l4 posterolateral herniation compressing the l3 nerve root with predisposition to irritate the left l4 root", on mri after a fall. does this sound normal for as or a distinct injury from the fall?

Although the 2 conditions can coexist, my reading shows that research has stated that AS does not cause herniated discs. Wear&tear and injuries do. I'm not sure what category of causes your disc herniation falls under but the fall could have caused it.

The trauma incurred from your fall is by far the cause of your disc herniation. The next step is to have an evaluation by a back surgeon to decide if surgery or physical therapy is the best direction.