Osteitis condensans ilii, also known as osteopathia condensans ilii or hyperostosis triangularis ilii in Germany, is characterised by benign sclerosis of the ilium adjacent to the sacroiliac (SI) joint, typically bilateral and triangular in shape.

Epidemiology

Osteitis condensans ilii has an incidence of 0.9-2.5%, and is much more common in women than men; primarily in pregnancy and the puerperium .

Clinical presentation

It is usually asymptomatic but uncommonly may cause axial lower back pain typically not centred over the SI joints, with a frequency of about 1-2.5% ⁴.

Pathology

Aetiology

The underlying aetiology 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 ^2-4. 

Radiographic features

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 ^3,4. 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 ³ (symmetric small focal sclerosis of the apposing sacrum is allowable though). Unilateral osteitis condensans ilii has been reported.

Treatment and prognosis

It carries a benign prognosis and may even resolve spontaneously.

History and etymology

It is thought to have been first described by Sicard, Gally, and Haguenau in 1926 ¹⁰.

Differential diagnosis

The main differential diagnoses are:

• sacroiliitis

• SI joint osteoarthritis

In osteitis condensans ilii, the sacroiliac joint is normal, with no irregularity, erosions, or loss of joint space.