Bone marrow edema of the sacroiliac joint without spondyloarthritis: 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 magnetic resonance imaging (MRI) of the sacroiliac joint (SIJ). Secondary objectives include comparisons of socio-demographic characteristics, prevalence of other imaging features (MRI, CTscan), 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 CTscan 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, MacNemartest) even if OCI was found in 4 nulliparous patients (15%). OCI patients experienced significantly more pain (p = 0.0026, MacNemartest). 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.