Aim Offering insight on pyogenic sacroilitis presenting as a limping child, a rare diagnosis of a common presenting complaint, affecting a mere 1.5% of all septic arthritis in childhood.

Methods Case report of a 3 year old girl with pyogenic sacroilitis presenting with an acute onset febrile illness limp and abdominal pain.

Review of the current literature on pathogenesis, diagnosis, and treatment of pyogenic sacroilitis.

Results Sacroillitis is a rare condition with non-specific clinical features, creating a challenging diagnosis for the clinician, often delaying appropriate management and potentially leading to avoidable complications. Based on the literature review biochemical and plain radiography make the condition hard to distinguish from other septic arthritis. Patients have an elevated temperature with an average of 38.5°C. The ESR is elevated with a mean ranging from 51-75 mm/h, as is the CRP with a mean of 4.7-30 mg/dL. There is also mild leucocytosis. The main pathogen is Staphylococcus aureus. Infections with E.coli, Staphylococcus epidermidis, Salmonella and Mycobacterium tuberculosis have been noted.

Plain radiographs are nonspecific. Delayed diagnosis can show sclerosis, lytic destruction and synostosis.

Ultrasonography of the joint is helpful in excluding a joint effusion.

Clinical suspicion and examination of the sacroiliac joint followed by MR imaging is the best route to diagnosis. Mainstay of treatment is intravenous antibiotics followed by a prolonged course of oral antibiotics. Rarely surgical intervention is needed.

Conclusion Sacroillitis is an uncommon clinical presentation in paediatric practice. Children present with fever, buttock pain and a limp. Diagnosis is missed as patients are often examined supine and SI joints are not examined routinely. Misdiagnosis of Appendicitis is also common. The situation is further obscured by the normal findings on plain radiograph and ultrasound. Therefore patients who present with evidence of infection, buttock pain and a gait abnormality should have there SI joint thoroughly examined, including the FABERE test and a referral for detailed imaging. These patients respond well to antimicrobial therapy and make a full asymptomatic recovery.