Osteitis condensans ilii
Osteitis condensans ilii, also known as osteopathia condensans ilii or hyperostosis triangularis ilii in Germany, is characterized by benign sclerosis of the ilium adjacent to the sacroiliac (SI) joint, typically bilateral and triangular in shape.
It is usually asymptomatic but uncommonly may cause axial lower back pain typically not centered over the SI joints, with a frequency of about 1-2.5% .
The underlying etiology is unknown but believed to be mechanical stress and imbalance across the SI joints causing a chronic stress response. Supporting this hypothesis, it is most often seen in women who have given birth; however, men and nulliparous women can be affected .
Plain radiograph and CT
Osteitis condensans ilii is often diagnosed incidentally. The iliac side of the SI joint demonstrates sclerosis which is typically bilateral, symmetrical, and triangular in shape . The sclerosis is sharply defined and dense, mainly in the anterior mid third of the joint. Lack of sacral involvement or joint space narrowing is considered diagnostic and may obviate the need for further imaging (symmetric small focal sclerosis of the apposing sacrum is allowable though). Unilateral disease has been reported.
Treatment and prognosis
It carries a benign prognosis and may even resolve spontaneously.
The main differential diagnosis is a sacroiliitis and SI joint osteoarthritis. With osteitis condensans ilii, the sacroiliac joint is normal, with no irregularity, erosions, or loss of joint space.