The sacroiliac joints are the two large joints at the back of the pelvis. They connect the sacrum (base of the spine) to the two pelvic bones (specifically the ilia). The SIJs are unusual joints in that they are not hinges or ball and sockets. The everyday role of the joints is not mobility, but shock absorption. Unlike smooth joint surfaces in the hip or knee, the SIJ surfaces are bumpy. As a result, the two bones fit together snugly like pieces of a puzzle. Mobility is reduced, but stability is increased. The presence of a number of large, strong ligaments around the joint further stabilise the area.
Symptoms of SIJ dysfunction
You might be able to find your own SIJs by feeling for two bony points in the small of your back. You may even be able to see them in a mirror, as “dimples of Venus”, but not everyone has these. Some people find that they can move something around over the joints, and when this is coupled with pain, they might be concerned. This mobile feeling is normal, and not a result of dysfunction.
Although it would make sense for the area of pain to correspond to the cause of the pain, the body is not that straight forward. See the diagram above for areas in which the SIJs can cause symptoms. Not all areas highlighted will be affected in every case. But it is easy to see how pain could be mistaken for sciatica.
There is also a lot of cross over between SIJ symptoms and those caused by the lowest spinal joints (L5/S1). Your osteopath will work to uncover the root cause of your symptoms.
Factors in SIJ dysfunction
Research suggests that SIJ dysfunction may be over-diagnosed in the general population. However, there are a few things that play a role in genuine SIJ dysfunction.
Pregnancy
Despite the SIJs limited movement, there is a time when their role has to change. When giving birth, the pelvis needs mobility to allow and assist the baby’s descent to the birth canal. The body’s solution to this is to relax the ligaments that support the joints. This change begins from early in the first trimester, as the hormone “relaxin” is produced. The combination of the growing bump and reduced pelvic stability can lead to lower back pain. Your osteopath may be able to help you manage this.
Because the pelvis is like a ring, a problem in one area can affect the other side or the front. The pubic symphysis is the thick cartilage joint at the front of the pelvis. In pregnancy, it can be particularly prone to irritation. When this is severe, it is known as PGP (Pelvic Girdle Pain), formerly SPD.
Rheumatology
We need to be aware of AxSpA when there is pain over the SIJ. AxSpA is an umbrella term that encompasses AS: ankylosing spondylitis. It is an autoimmune, inflammatory condition in which the body attacks its spinal joints and SIJs. During inflammatory episodes, pain increases, and the patient may generally feel under the weather. Once the inflammation subsides, the body attempts to heal the damage. Instead it lays new bone over the joints themselves.
It is important that you are referred to rheumatology if your pain is caused by an autoimmune condition like this. We can help support you in this if it is suspected. You can read more about AS and AxSpA on our blog here.
