The SI joint acts as a shock-absorbing structure for the body. It is small and strongly reinforced with ligaments and is not highly mobile. While the causes of SI pain are not well understood, they can include:
• Too much movement in the SI joint. This leads to lower back pain that radiates into the groin area.
• Too little movement in the SI joint. When it is too tense, this can lead to pain in the lower back or in one side or the other of the buttocks. This pain can often be felt radiating down the leg. It will often feel similar to sciatica.
These can occur after abnormal movements at work or during sports. An injury such as a fall onto the buttocks or the shock absorbed after missing a step while descending stairs can lead to SI joint pain. Motor vehicle accidents can also cause an impact that results in SI pain.