Purpose or Case Report: To investigate magnetic resonance (MR) imaging features of sacroiliac joint infections in children with respect to age and with clinical correlation.
Methods & Materials: This IRB-approved, HIPPA compliant study included 40 MR studies with sacroiliac joint infections from 40 children (mean age 8.62 +/- 6.1 years; 19 boys and 21 girls) performed between December 1, 2002 and July 31, 2018. Infections were established using a combination of positive cultures, elevated inflammatory markers, clinical assessment, and response to antibiotic treatment. MR studies were retrospectively reviewed by 2 radiologists in consensus for the presence of bone marrow edema, bony erosions, joint effusion, extracapsular edema, soft tissue abscess, and sciatic neuritis. Pre-treatment radiography was reviewed for the presence of radiographically visible osseous change. Clinical chart review was performed for clinical history and outcomes. Descriptive data is presented as mean ± SD. The inter-observer agreement was evaluated with weighted-kappa. Kappa scores (k) of 0.41–0.60, 0.61–0.80 and ≥0.80 were regarded to be indicative of moderate, good, and excellent agreement, respectively. Non-parametric, Chi-square and Fisher tests were used, p < 0.05 was considered significant.
Results: A bimodal age distribution for infectious sacroiliitis was identified with 40% (16/40) from children ≤ 5 and 60% (24/40) from children ≥ 8 years of age. No difference was found between the groups in the presence of bone marrow edema, bony erosions, joint effusion, and soft tissue abscess. Although anterior extracapsular edema was present in all patients, posterior extracapsular edema was more common in the younger age group (p=0.006, k=0.923). Radiographically visible osseous changes were often not present at the time of diagnosis. 80% of patients had diagnostically adequate radiography within a month prior to MRI (3.6 ± 4.6 days between studies). The ability to identify infection using radiography was poor, at 31%. Clinically, the mean duration of symptoms was 8.6 ± 7.4 days and length of hospital stay was 7.8 ± 4.1 days, which did not differ between the age groups (p=0.28 for symptom duration, p=0.24 for hospital stay).
Conclusions: Clinical findings and many of the MR imaging features of infectious sacroiliitis in children did not significantly differ with respect to age. Posterior extracapsular edema was more common in younger children, which suggests regional ligamentous and capsular laxity and immaturity.