Why, How, Who. Epidemiology? SI, Differential what?

This sounds like a good bedtime story. Actually it's pretty interesting. As we gather an understanding of a particular problem in medicine, we want to see where it goes, what happens to it, who gets it and who develops this problem and why they develop this problem. We're putting the building blocks down of understanding how to approach a patient in pain. Actually, any patient. It's called the natural history. Not particularly cool sounding, but is a very important fundamental to understand where you're going to be not now, but in 3, 6, 9 and 12 months. Also, woven into this is the differential diagnosis. The differential diagnosis of a disease state is "what it can be." Based on physical findings, historical elements, and just plain common sense and experience can be the key to unlocking a medical problem, and defining Rule 2. 

Finally, the sacroiliac joint is one of the most common pain generators and often completely misunderstood. We're touching on this, it's a start of a discussion about sacral joint pain, not complete, but we're building.