Bone marrow oedema of the sacroiliac joint without spondyloarthritis: a retrospective study of 34 cases of osteitis condensans ilii.

Objective: To determine the prevalence of bone marrow oedema (BME) in osteitis condensans ilii (OCI) on MRI of the sacroiliac joint (SIJ). Secondary objectives include comparisons of socio-demographic characteristics, prevalence of other imaging features (MRI, CT scan), and low back pain in patients with OCI with those in a sex- and age-matched control group.

Methods: A total of 34 patients with OCI, including 29 with MRI, were recruited for retrospective analysis. The SIJ MRIs were retrospectively analysed by two readers. A sex- and age-matched control group of patients without SIJ disorders was included. In both groups, the presence of structural bone abnormalities was assessed by CT scan analysis, and socio-demographic data were obtained by telephone questionnaire. A longitudinal analysis was conducted on patients who had undergone multiple imaging examinations.

Results: All patients were female with a mean age of 34 years. BME was observed in 66% (19/29) of OCI patients. BME in OCI was mainly located in the anterior-middle quadrant (43.48%). OCI patients had significantly more than one delivery (P = 0.0094, McNemar test), even if OCI was found in four nulliparous patients (15%). OCI patients experienced significantly more pain (P = 0.0026, McNemar test).

Conclusion: OCI is an entity found in both pregnant and non-pregnant young women. SIJ BME was found in two-thirds of OCI patients. OCI is a significant cause of BME and should be carefully considered by clinicians when dealing with a patient with low back pain in order to avoid misdiagnosing spondyloarthritis in the presence of BME of the SIJ.