Lower back pain knots on either side of spine at belt line.?

A few years ago I had an accident in which I was hit with a huge rock in the back. I never broke anything , but these "knots" appeared on either side of my spine around my belt line. These inflame from time to time and send stabbing pains down my hips into my legs. I can push on the knots and the same thing happens. What are these things? I am seeing a doc know who thinks I have SI joint problems but do these knots have anything to do with disk problems? Does anyone know? We have done a n x ray that shows arthritis and degenerative disease. My doc told me we wouldn't talk about disk trouble yet. That makes no sense to me at all.