A sacroiliac joint injection is an injection into the sacroiliac joint. The sacroiliac joint - just for anatomy's sake - here's the pelvis. This is the front. This is the back. This is the sacrum; and this bone right here is the ilium. This joint line is the sacroiliac joint.
A sacroiliac joint injection is where we put medicine into the joint. We do this for two important reasons. The first is diagnostic. The gold-standard diagnosis of sacroiliac joint pain is to put a needle into the joint - under an x-ray - and put some lidocaine or some novocain there in order to see if the pain goes away. When the pain goes away, that confirms the diagnosis of sacroiliac joint pain. We often also put steroid into the sacroiliac joint while we're putting the needle in. The steroid is an anti-inflammatory and that can help to reduce the inflammation, reduce the swelling, and take away the pain allowing someone to get in, again with physical therapy and exercises in order to keep the pain from returning.