Causes of Sacroiliac joint pain can be split into four categories; traumatic, biomechanical, hormonal and inflammatory joint disease.
The concept of the SIJ causing lower back pain is now pretty well understood. However, due to the complex anatomy and movement patterns at the joints and area in general, evaluation and treatment of sacroiliac dysfunctions is still controversial.
What are the sacroiliac joints?
The Sacroiliac joints are located at the very bottom of the back. You have one either side of the spine. The Sacroiliac joints help make up the rear part of the pelvic girdle and sit between the sacrum bone and the Ilia or hip bones.
The function of the SI joints is to allow torsional or twisting movements when we move our legs. The legs act like long levers and without the sacroiliac joints and the pubic symphesis (at the front of the pelvis) which allow these small movements, the pelvis would be at higher risk of a fracture.
SIJ dysfunction is a term which is commonly used when talking about sacroiliac injuries. This dysfunction refers to either hypo or hyper mobility (low or high respectively). In other words, the joint can become 'locked' or be too mobile.
This can then lead to problems with surrounding structures such as ligaments (e.g. Iliolumbar ligament) and muscles, which means SIJ problems can cause a wide range of symptoms throughout the lower back and buttocks, or even the thigh or groin.
Traumatic injuries to the SIJ are caused when there is a sudden impact which 'jolts' the joint. A common example is landing on the buttocks. This kind of injury usually causes damage to the ligaments which support the joint.
Biomechanical - Pain due to biomechanical injuries will usually come on over a period of time and often with increased activity or a change in occupation/sport etc. The most common biomechanical problems include leg length discrepancy, over pronation, twisted pelvis and muscle imbalances
Hormonal changes, most notably during pregnancy can cause sacroiliac pain. In preparation for giving birth, the ligaments of the pelvis especially increase in laxity. Combining this with an increase in weight putting extra strain on the spine, may lead to mechanical changes which can result in pain.
Inflammatory Joint Disease - Spondyloarthropathies are inflammatory conditions which affect the spine. These include Ankylosing Spondylitis which is the most common inflammatory condition to cause SI joint pain.