Sacroiliac joint syndrome of SIJ syndrome for short, generally refers to pain in the SIJ region that is caused by abnormal motion in the SIJ (can be too much or too little).
We refer to it as a “syndrome” as there can be multiple reasons for pain in this region. Not only are the joint surfaces a possible pain generator, but there are multiple muscles and ligaments that surround and attach to the SIJ at the front and back. These may also contribute to the pain pattern.
I can only assume that your diagnosis is correct, however most people complain of pain in the lower back, occasional referred pain into the buttock, groin or hip. Pain does not usually travel past the knee.
In practice, we have a special interest in the role that the SIJ has in low back and spinal function. Every body is unique and requires a tailored approach. I suggest that you listen to your health care professional and follow their lead. In my experience, SIJ syndrome responds well to manual therapies.