Iwas at the PT today and asked, out of curiosity, to see the spine model. He was very happy to show it to me. He told me that in some people, the SI is jointed one more joint than in others, thus the L6. So, there is extra movement. This causes instability in some people. In some, it causes scoliosis. It makes for more work in fusing lumbar patients that have it. This usually makes them a level 2 instead of a level 1.
He also went into details on fusion of the L5 and SI, not something that I ever want to have done. But then, who does. He showed me where the sciatic nerve exits and why some people suffer from sciatica.
He was a very thourough PT/Chiropractor. I liked him because he stated that if he could not help in four treatments, then he doesn't milk anyone for more money.