This is an asymptomatic condition of the ilium that is often confused with sacroiliitis on roentgenographic study of the pelvis. There is a high female to male ratio in the patients involved. Osteitis condensans ilii is a well-defined triangular sclerosis of the ilium adjacent to the sacriliac joint. It is typically, though not universally, bilateral. There is no sclerosis of the sacrum and the sacriliac joint remains normal. The size of the iliac sclerosis may vary considerably. The condition may resolve with time. There are no symptoms. Symptoms occurring in that area should be attributed to some other cause.
The cause is not clear but appears to be mechanical stress across the sacroiliac joint along with the vascularity associated with pregnancy. It sometimes occurs in nulliparous women and men, presumably due to other sources of mechanical stress.
Like any diagnosis, this may cause some anxiety. The patient may have been told that they have ankylosing spondylitis. Explaining the correct diagnosis and that no treatment is indicated can be reassuring.