[Osteomyelitis: a probable, uncommon etiology agent]

The relation of infectious agents to arthritis is an area of great interest to the rheumatologist. Septic arthritis of bacterial origin accounts for approximately 6.5% of all childhood arthritides. Septic arthritis usually results from haematogenous spread from a focus of infection elsewhere in the body, but also by direct extension of an infection from overlying soft tissues or bone or traumatic invasion of the joint. As a result, if a focus of underlying osteomyelitis breaks throught the metaphysis, it may enter the joint and result in septic arthritis. Systemic signs of illness are fever, severe bone pain, and tenderness with or without local swelling. A wide range of microorganism can cause septic arthritis in children; Staphylococcus aureus and nongroup A and B streptococci are most common overall. However, different organisms are more common at some ages and in certain circumstances. Kingella kingae is an emerging pathogen in young children under 4 years of age. The clinical presentation of K. kingae invasive infection is often subtle and may be associated to mild to moderate biologic inflammatory responses. Affected children often have few signs and symptoms of osteoarticular infections. Early MRI is useful in differentiating K kingae from Gram-positive cocci in osteoarticular infections. Cartilaginous involvement, modest soft tissue and bone reaction suggest K. kingae. It's very important to include K. kingae in differential diagnosis of osteoarticular infections in young children. We report an unusual case of osteomyelitis: clinical manifestations and MRI are suggestive for K kingae infection.