The Sacro-Iliac joint is a common cause of lower back pain due to the large amount of force it has to cope with, patients often get this joint confused with the hip as it is quite low and slightly to the side of the spine.
Pain that originally starts in this region often spreads across the whole of the lower back, this is because inflammation is a very clever but also very crude system. When the inflammatory process starts, it essentially dumps inflammatory chemicals on a region. What it often does however is go a bit too far, this can actually damage healthy cells, giving the feeling of pain in a general region.
The S.I. joint can also refer pain to various other regions, this is because where the pain fibers from the S.I joint enter the spine, fibers often cross with fibers that innervate other regions of skin of the body, therefore producing pain at the region also. When this occurs, it is known as an S.I. joint Syndrome as all three components of pain, restriction and pain referral are involved to make up the ‘syndrome’
Regions that the sacroiliac joint has been known to refer pain to (in grey):
There are more serious conditions that can affect this joint such as various arthropathies, (there are many types of arthritis) though a well trained Chiropractor should be able to determine the exact cause of the pain from your history and assessment. As I always say though, make sure your Chiropractor is well recommended and also provides good treatment for at least 15-20 minutes as this is a good sign of a Chiropractor doing their job properly.