Sacroiliitis is an inflammation of one or both of your sacroiliac joints – situated where your lower spine and pelvis connect. Sacroiliitis can cause pain in your buttocks or lower back, and can extend down one or both legs.
Sacroiliitis can be difficult to diagnose, because it can be mistaken for other causes of low back pain. It’s been linked to a group of diseases that cause inflammatory arthritis of the spine. Sacroiliitis can be aggravated by prolonged standing, bearing more weight on one leg than the other, stair climbing, running, and taking large strides.
Causes for sacroiliitis include traumatic injury, arthritis, pregnancy, and infection. As with other conditions that cause chronic pain, sacroiliitis can result in depression and insomnia.
Sacroiliitis, Mayo Clinic (Dec. 30, 2017), https://www.mayoclinic.org/diseases-conditions/sacroiliitis/symptoms-causes/syc-20350747