O3251: When the Sacroiliac Joint Is the Culprit: A Multicenter Investigation of an Uncommon Primary Location for Pediatric Musculoskeletal Infections

Background: Pediatric musculoskeletal infections (MSKI) affecting the sacroiliac joint (SIJ) account for less than 1% of cases. Current literature leaves several gaps regarding appropriate detection and clinical management. The purpose of this multicenter study is to describe findings that facilitate diagnosis, while identifying factors associated with a more challenging clinical course.

Methods: A query was conducted between 01/01/2000 and 03/02/2021 at three large academic institutions. We included patients < 18 years old with clinical findings consistent with pyogenic infection and either positive specimen cultures (blood or bone) or radiographically confirmed SIJ involvement. Descriptive statistics were used to analyze the data in the form of frequencies (%) and means (%). We employed logistic and linear regression analysis to evaluate which variables could predict outcomes of interest including operative intervention, length-of-stay, and complications.

Results: We included 69 patients; the average age was 12.0 years, and less than 25% had co-morbidities. Common presenting symptoms were pain localized to the posterior pelvis or SIJ (94%) and difficulty with ambulation (94%). Irritable hip motion was present in 93% of patients, though less than 25% had a positive FABER test. Associated symptoms were present in 48% of patients (chills or sweats - 21.7%, nausea/vomiting - 15.9%). The maximum CRP and ESR averaged 14.5 and 70, respectively. The mean duration of antibiotic therapy was 41.9 days. X-rays performed the day of admission (86%) were predominantly normal (89%). MRI findings included edema and bony changes in the SIJ (54%), with spread to muscle (95.4%). Staphylococcus aureus was the most common pathogen (88%), with 10% found to be MRSA. 18% of patients had CT-guided aspirate and 20% of patients had at least one operative procedure, with incision and drainage of the SIJ as the most common (64%). Recurrent or chronic infection was uncommon (8.7% and 5.8%, respectively), as were inpatient complications (8.7%). The average hospital stay was 9.1 days. On further analysis, max CRP was positively associated with the odds of surgical procedure, and increased age was positively associated with the odds of inpatient complications (p < 0.05). BMI was positively associated with inpatient LOS (p=0.055). Total duration of antibiotic therapy was significantly longer in patients in the operative group (p=0.01).

Conclusion: This multicenter study provides a comprehensive description of pediatric SIJ infections. We identify several key factors that can aid in the diagnosis and management of SIJ infections, including focal posterior pelvis or SIJ pain, irritable hip motion, ambulatory difficulty, elevated ESR/CRP, and fever/chills. Early MRI is preferred to confirm the diagnosis. In uncertain cases, CT-guided biopsy or operative intervention can be effective tools for both diagnosis and treatment. Some patients may require one or multiple procedures and extended antibiotic duration, yet outcome was largely satisfactory at most recent follow-up.