How does the SI joint cause pain?

The SI joint is a synovial joint. This type of joint has free nerve endings that can cause pain if the joint degenerates, does not move properly, or does not properly accommodate the forces that cross the joint. The SI joint has been long known to cause pain in the lower back and buttocks. Like any other joint in the body, the SI joint can become arthritic or its supporting ligaments may be injured. When this happens, people can feel pain in their back, especially with lifting, running or even walking. In these cases, the pain is sometimes similar to the pain caused by a “disc” or spinal arthritis.