In assessment of septic arthritis, the majority of pediatric patients with septic arthritis were noted on MRI to have infection beyond the joint space, though this may vary based on population factors such as geography [7,46,60,65,66]. Conversely, in metaphyseal osteomyelitis, >50% in one study were noted on MRI to have concomitant joint effusions, 75% of which were confirmed to be septic arthritis [67]. Osteomyelitis or Septic Arthritis-Child MRI Extremity Area of Interest In one study, a large field-of-view MRI was performed to encompass both lower extremities rather than the area of concern [38]. In patients who were later found to have osteomyelitis, 11% had contralateral extremity findings, including contralateral osteomyelitis, and 20% had ipsilateral septic arthritis. Among patients who did not have osteomyelitis, 20% had contralateral abnormalities, most commonly stress reaction, soft-tissue edema, myositis, joint effusion (not septic), and leukemia. Radiography Area of Interest Radiographs are not sensitive in assessment of early osteomyelitis because bone destruction does not typically occur until 7 to 10 days into the disease course, and radiographs are normal until >30% osseous matrix destruction has occurred [24,40]. Radiographs, however, do have utility in all populations in excluding other entities that may mimic acute osteomyelitis, such as fracture or neoplasm [3,25,31,40]. Radiographs are highly variable in identifying hip joint effusions, with sensitivity ranging from 20% to 73% [40,42,43]. US Area of Interest US is a highly sensitive method of diagnosing hip joint effusion, and the absence of hip joint effusion virtually excludes septic arthritis; a false negative rate of 5% has been described, noted in patients with a shorter duration of symptoms (<1 day) [40,43,45-47]. US can reportedly detect hip effusions as small as 1 mL [44].
Osteomyelitis or Septic Arthritis Child Excluding Axial Skeleton PCAs. In assessment of septic arthritis, the majority of pediatric patients with septic arthritis were noted on MRI to have infection beyond the joint space, though this may vary based on population factors such as geography [7,46,60,65,66]. Conversely, in metaphyseal osteomyelitis, >50% in one study were noted on MRI to have concomitant joint effusions, 75% of which were confirmed to be septic arthritis [67]. Osteomyelitis or Septic Arthritis-Child MRI Extremity Area of Interest In one study, a large field-of-view MRI was performed to encompass both lower extremities rather than the area of concern [38]. In patients who were later found to have osteomyelitis, 11% had contralateral extremity findings, including contralateral osteomyelitis, and 20% had ipsilateral septic arthritis. Among patients who did not have osteomyelitis, 20% had contralateral abnormalities, most commonly stress reaction, soft-tissue edema, myositis, joint effusion (not septic), and leukemia. Radiography Area of Interest Radiographs are not sensitive in assessment of early osteomyelitis because bone destruction does not typically occur until 7 to 10 days into the disease course, and radiographs are normal until >30% osseous matrix destruction has occurred [24,40]. Radiographs, however, do have utility in all populations in excluding other entities that may mimic acute osteomyelitis, such as fracture or neoplasm [3,25,31,40]. Radiographs are highly variable in identifying hip joint effusions, with sensitivity ranging from 20% to 73% [40,42,43]. US Area of Interest US is a highly sensitive method of diagnosing hip joint effusion, and the absence of hip joint effusion virtually excludes septic arthritis; a false negative rate of 5% has been described, noted in patients with a shorter duration of symptoms (<1 day) [40,43,45-47]. US can reportedly detect hip effusions as small as 1 mL [44].