Variation in the appearance of the normal sacroiliac joint on pelvic CT

Objective: To describe the CT appearance of the ageing sacroiliac joints (SJ) and correlate the radiological findings with patients' gender, body mass index (BMI) and, in women, parity. Materials and Methods: The study population included 288 consecutive patients who underwent pelvic CT for various indications not related to SJ diseases. Patients were stratified by age, BMI and parity in women. The joint space and subchondral sclerosis were assessed and the presence of osteophytes, ankylosis, erosions, subchondral cysts and vacuum phenomena were noted on bone window settings. Results: The widths of the SJ space and of the subchondral sclerosis on the iliac and sacral sides were 2.3+/-0.4 mm, 2.5+/-1.6 mm and 1.4+/-0.5 mm, respectively, in patients younger than 40 years of age and 1.9+/-0.2 mm, 3.6+/-2.1 mm and 2.3+/-1.1 mm, respectively, in patients older than 40 years of age. The joint space tends to become narrow and less uniform with advancing age, while subchondral sclerosis appeared to be wider and less uniform in the elderly. Osteophytes were present even in younger patients and their prevalence increased with advancing age. Ankylosis and erosions were rare findings, observed only after the fifth decade of life. A higher prevalence of asymmetric non-uniform SJ space, ill-defined, non-uniform, extensive subchondral sclerosis and ankylosis was observed in women, obese and multiparous mothers than the age matched men, normal weighted individuals and non-multiparous women, respectively. Conclusion: Conventional pelvic CT can provide valuable information concerning the SJ, when reviewed on bone window settings. The CT appearance of the SJ is closely related to patients age, gender, BMI and, in women, parity. Knowledge of the spectrum of radiological findings observed in the normal population may be useful when interpreting examinations of patients with SJ disease.