Can early MRI distinguish between Kingella kingae and Gram-positive cocci in osteoarticular infections in young children?

K. kingae is a common causative organism in acute osteoarticular infections (OAIs) in children under 4 years of age. Differentiation between K. kingae and Gram-positive cocci (GPC) is of great interest therapeutically. Our aim was to identify early distinguishing MRI features of OAIs. Thirty-one children younger than 4 years of age with OAI underwent MRI at presentation. Of these, 21 were caused by K. kingae and ten by GPC. Bone and soft tissue reaction, epiphyseal cartilage involvement, bone and subperiosteal abscess formation were compared between the two groups. Interobserver agreement was measured. Bone reaction was less frequent (P = 0.0066) and soft tissue reaction less severe (P = 0.0087) in the K. kingae group. Epiphysis cartilage abscesses were present only in the K. kingae group (P = 0.0118). No difference was found for bone abscess (P = 0.1411), subperiosteal abscess (P = 1) or joint effusion (P = 0.4414). Interobserver agreement was good for all criteria. MRI is useful in differentiating K. kingae from GPC in OAI. Cartilaginous involvement and modest soft tissue and bone reaction suggest K. kingae.