Findings of hip effusion associated with bone marrow edema or decreased enhancement of the femoral head should raise the possibility of septic arthritis [70,71]; although, definite diagnosis of septic arthritis requires joint aspiration and fluid analysis. Contrast administration in the MRI evaluation of suspected soft-tissue or osseous infection does not increase sensitivity or specificity but increases reader confidence and better delineates abscesses [50,51]. An exception to this may be in infants and younger children with an abundance of nonossified cartilage, in whom infection limited to the intrinsically hyperintense cartilaginous growth plate and epiphyses/apophyses can be occult on unenhanced MRI sequences. Given these considerations, the use of IV contrast may vary with institutional protocol. Variant 5: Child up to age 5. Acute limp. Symptoms localized to lower extremity (not pelvis or hips). Concern for infection. Initial imaging. The body regions covered in this clinical scenario are: femur, knee, tibia/fibula, ankle, and foot. Radiography Lower Extremity There are limited evidence to support the use of radiographs for the acute evaluation of localized infection. The sensitivity of radiographs in detecting early osteomyelitis or soft-tissue infection is low [39,40]. While soft-tissue signs of swelling and edema may be detected early by radiographs and nonspecific signs, such as periosteal reaction and osteopenia, detection of bone destruction may take up to 3 weeks after onset of symptoms [54,64,72]. US Lower Extremity US may play a role in diagnosing pyomyositis, in which inflammatory change may lead to an altered sonographic appearance in affected muscle [73,74]. Because US will not penetrate cortex, it is unable to evaluate bone marrow and is not sensitive for osteomyelitis. US is sensitive to subperiosteal collections, which can be seen with osteomyelitis [54,75].
Acutely Limping Child Up To Age 5 PCAs. Findings of hip effusion associated with bone marrow edema or decreased enhancement of the femoral head should raise the possibility of septic arthritis [70,71]; although, definite diagnosis of septic arthritis requires joint aspiration and fluid analysis. Contrast administration in the MRI evaluation of suspected soft-tissue or osseous infection does not increase sensitivity or specificity but increases reader confidence and better delineates abscesses [50,51]. An exception to this may be in infants and younger children with an abundance of nonossified cartilage, in whom infection limited to the intrinsically hyperintense cartilaginous growth plate and epiphyses/apophyses can be occult on unenhanced MRI sequences. Given these considerations, the use of IV contrast may vary with institutional protocol. Variant 5: Child up to age 5. Acute limp. Symptoms localized to lower extremity (not pelvis or hips). Concern for infection. Initial imaging. The body regions covered in this clinical scenario are: femur, knee, tibia/fibula, ankle, and foot. Radiography Lower Extremity There are limited evidence to support the use of radiographs for the acute evaluation of localized infection. The sensitivity of radiographs in detecting early osteomyelitis or soft-tissue infection is low [39,40]. While soft-tissue signs of swelling and edema may be detected early by radiographs and nonspecific signs, such as periosteal reaction and osteopenia, detection of bone destruction may take up to 3 weeks after onset of symptoms [54,64,72]. US Lower Extremity US may play a role in diagnosing pyomyositis, in which inflammatory change may lead to an altered sonographic appearance in affected muscle [73,74]. Because US will not penetrate cortex, it is unable to evaluate bone marrow and is not sensitive for osteomyelitis. US is sensitive to subperiosteal collections, which can be seen with osteomyelitis [54,75].