A 9-month-old baby presented with sudden inability to stand and unable to move his leg. Clinical examination showed edema and knee effusion. Blood tests and MRI confirmed septic knee arthritis without bone involvement. He was treated with arthroscopic lavage. He had a complete recovery and normal growth.
FIGURE 1 A, B Continuous kicking of the right leg and absent movements of the left leg
FIGURE 2 A, Sagittal STIR sequence demonstrates an extensive amount of fluid in the knee joint, a finding accompanied by edematous appearance of the muscles around the joint and a small amount of fluid in the intermuscular spaces. There is no apparent bone marrow edema. B, Axial STIR sequence. The intraarticular effusion is well delineated in the transverse plane, as well as the small amount of fluid around the muscles of the posterior compartment of the tibia. C, Sagittal MERGE sequence demonstrates intact articular cartilage of the knee joint
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FIGURE 3 Arthroscopic picture with infected and hypertrophied synovium, in front of the ACL
