My doctor and my physical therapist agree that my back and leg pain are really coming from my sacroiliac (SI) joint. How is that really possible? Shouldn't the pain be right over my SI?
There are many soft tissue and bony structures that make up the sacroiliac joint (SIJ). The basic joint is formed where the sacrum meets the two bones of the pelvis. The main pelvic bone (ilium) also helps form the socket for the hip joint. And the sacrum sits right underneath the last lumbar vertebra.
So, just using the bone connections as a possible source of pain doesn't include all possible causes. There are also ligaments in the joint, around the joint (joint capsule), and the joint articular surface. Damage to any of the ligaments, muscles, or nerves in the sacroiliac joint region can contribute to pain.
And that's another thing: pain in the sacroiliac area can be coming from someplace else like the low back area. And problems with the sacroiliac joint can refer pain to other areas such as the low back, buttock, or leg.
All of this is potentially confusing and difficult to figure out. There isn't just one test the examiner can perform and say Aha! It's the sacroiliac joint that's causing the pain. Instead, they must rely on several different clinical tests. Most of these tests are provocative. This means they are designed to stretch, pull, or compress the sacroiliac joint and reproduce the symptoms.
Another diagnostic method is an intraarticular joint injection. The surgeon inserts a long, thin needle into the sacroiliac joint and injects a numbing agent and antiinflammatory drug. Since the fluid injected can leak out of the joint into the surrounding area, it's not 100 per cent diagnostic of an intraarticular problem when the pain goes away.
It sounds like whatever method was used to diagnose your pain, there is agreement as to the nature of your problem. That's great because it isn't always possible to clearly identify the cause and get the right treatment plan going. You've conquered more than half the battle just getting an accurate diagnosis!