Pediatric Musculoskeletal Imaging
Pediatric musculoskeletal imaging requires familiarity with normal growth and with fracture patterns unique to children. The physis is the weak link, so Salter-Harris injuries are common; type I may be radiographically normal and is suspected clinically or by MRI. Buckle (torus) fractures show cortical buckling, greenstick fractures show one cortex broken and the other bent, and plastic deformation occurs without a visible fracture line. A toddler's fracture is a subtle spiral tibial fracture that may need oblique views or follow-up imaging. Do not mistake normal metaphyseal irregularity, physiologic periosteal reaction, or accessory ossification centers for injury.
In nonaccidental trauma, look for classic metaphyseal lesions, posterior rib fractures, scapular and spinous process fractures, and multiple fractures of differing ages; a skeletal survey is indicated in young infants. In the hip, developmental dysplasia is screened by ultrasound in early infancy using Graf angles; Legg-Calve-Perthes affects boys 4-8 years with femoral head fragmentation; slipped capital femoral epiphysis affects older children and shows failure of Klein's line to intersect the femoral head on AP view, confirmed on frog-leg lateral. Osteomyelitis typically begins in the metaphysis. Ewing sarcoma is diaphyseal with permeative destruction and onion-skin periosteal reaction, while osteosarcoma is metaphyseal with osteoid matrix and sunburst periosteal reaction. Also know rickets, scurvy, Langerhans cell histiocytosis, and osteochondroma.
Worked rule: A child with a limp and hip pain gets an AP pelvis and frog-leg lateral; if these are normal and suspicion remains, obtain MRI rather than repeat radiographs.