The pelvis connects to the spine at the sacrum. (The sacrum is the triangular bone in the lower spine that fits between the bones of the pelvis.) This connection is called the sacroiliac joint (SIJ). The SIJ may not move much, but it can still cause a lot of pain if it isn’t functioning well.
SIJ problems can be a source of chronic pain. The pain often radiates to the groin, buttocks, thigh, and even to the foot or abdomen on the same side as the painful joint. SIJ pain can happen after surgery to fuse vertebrae of the lumbar spine and the sacrum. Doctors think this is because the fusion shifts force onto the SIJ.
The problem with pain caused by SIJ is that it is hard to diagnose. Several other problems can cause similar symptoms. Physical exams, X-rays, and other types of scans may help rule out some of these other problems, but they do not positively identify a painful SIJ. The only way to tell seems to be to inject a local anesthetic into the SIJ and see if the patient feels pain relief.
These authors looked at records for 34 patients in their spine clinic who needed an SIJ injection after having fusion of the low back vertebrae to the sacrum. Over half of the patients had greater than 75 percent relief of their pain 45 minutes after the SIJ injection. Another 18 percent got some pain relief. But 24 percent had no pain relief from the injection.
Bone graft material used to fuse vertebrae is sometimes taken from the top of the pelvis bone. The authors found no relation between SIJ pain and whether bone graft was taken from the pelvis. Only 25 percent of the patients in this study had bone taken from the pelvis. In these patients, there was no relationship between the side of the SIJ pain and the side where surgeons had gotten the bone graft.
Based on these results, the authors concluded that the pain in about one-third of the patients definitely came from the SIJ. The pain was “possibly” caused by the SIJ in another 29 percent of the patients. The authors suggest further research to better understand SIJ pain after lumbar fusion surgery.