Preliminary MRI Study on Sacroiliac Joint Anatomy: Does Morphology Matter?

 

Purpose: Anatomical and radiologic studies with computed tomography have reported variations in sacroiliac joints (SIJs). However, even though magnetic resonance imaging (MRI) plays a crucial role in the diagnosis of spondyloarthropathies (SpA), only a few MRI studies have been conducted on SIJ anatomy. The purpose of this study was to investigate whether different joint morphologies have clinical significance and are associated with imaging findings.

Methods and Materials: Sacroiliac MRIs of 79 patients (43 patients with early SpA and 36 controls) at different times were analyzed retrospectively for anatomical configuration of the anterior and posterior (ligamentous) parts of the joints and periarticular variations (transitional vertebra at lumbosacral junction, deep paraglenoid sulci) (Figs. 1–4). Additionally, blinded to the diagnoses, SIJ MRIs of all cases were evaluated for structural lesions (subarticular sclerosis, fatty infiltration), bone marrow edema, and minor inflammatory lesions (joint effusions, enthesitis).

Categorical variables were assessed by the chi-square test or Fisher exact test, where applicable. Difference between two groups for continuous variables was evaluated by the Student t test. To define risk factors of outcome variables, multiple logistic regression analysis was used, and odds ratios (ORs) were calculated. A p < 0.05 was considered significant.

Results: The mean ages of SpA subjects and controls were 40.9 (± 9.3) and 42.4 (± 11.4) years, and the mean follow-up intervals were 21 (± 11.4) and 21(± 11.7) months, respectively. There were 15 men (7 in the SpA, 8 in the control groups) and 64 women (36 in the SpA and 28 in the control group). There were no statistical differences with regard to age or sex in either group (p > 0.05).

SIJ variations were significantly more common in the control group (p = 0.016). Posterior SIJ variations were more common in women both on the right (p = 0.029) and left (p = 0.003) sides.

No particular joint type with regard to various anatomical shapes on either side or group was found to be significantly more common.

There were noteworthy correlations between the presence of minor lesions on the right and left sides and contralateral periarticular variations (p = 0.033 and p = 0.045, respectively).

The presence of right anterior SIJ variations, left periarticular variations, and SpA showed increased risk for development of right-sided minor inflammatory changes (p = 0.012, 0.003, and 0.014) (OR: 7.3; 95% confidence interval [CI], 1.5–34.5; OR: 18; 95% CI, 2.6–122.1; and OR: 11.2; 95% CI, 1.6–77.4, respectively). For bone marrow edema, only the presence of SpA was found to be a risk factor (p = 0.004; OR: 10.1; 95% CI, 2.1–47.7).

Conclusion: Morphological variations in SIJs on the anterior, posterior parts, and periarticular variations between individuals may have clinical significance beyond being simply incidental findings on imaging. Although further studies with more cases are required, this preliminary study offers important clues to radiologists that SIJ morphology matters.