Paediatric Imaging

Slipped capital femoral epiphysis

(SCFE), a chronic SalterHarris I fracture through the physis of the proximal femur with relative slip of the epiphysis. The capital femoral epiphysis usually remains located in the acetabulum but the femoral shaft is displaced anterolaterally, resulting in a relative posteromedial slip of the epiphysis (see physeal fracture). The condition presents with hip pain and limp and typically occurs during the pubertal growth spurt. There is an increased incidence in overweight children which probably reflects the increased shear stresses on the physis. Acute trauma or repetitive stress injury is the usual cause but there are also recognized associations with hypothyroidism, renal osteodystrophy, hypogonadism and pseudohypoparathyroidism suggesting hormonal influences. It can also be seen following local radiation therapy in the region of the hip.

The risk of contralateral slip is 912% at presentation but this risk increases with time until skeletal maturity is reached. Subtle slips can be difficult to detect on a frontal projection and a frog lateral radiograph of the pelvis is the preferred first line investigation (Fig.1). The femoral head and neck typically show reduced radiodensity, the epiphyseal height appears reduced and the physis widened (reflecting angulation), often with reactive sclerosis in the metaphysis. A line drawn tangential to the lateral border of the femoral neck should normally intersect approximately one sixth of the capital femoral epiphysis, whereas with SCFE the extent of the epiphysis intersected is less. Conventional radiographs usually suffice for diagnosis but CT (Fig.2) can aid surgical planning in a severe slip. The objectives of treatment are to prevent further displacement and stimulate early physeal fusion by internal fixation of the epiphysis relative to the femoral neck.

The potential sequelae of SCFE include avascular necrosis of the epiphysis, chondrolysis and osteoarthritis. Avascular necrosis (AVN) has been reported in 615% and is more frequent after attempted reduction, severe slip (Fig.3) or delayed treatment (see avascular necrosis). Chondrolysis represents acute cartilage necrosis and has been reported in up to 40% with an increased incidence in the Afrocaribbean population, but it only appears clinically significant in approximately 10%. It is usually recognized within 1 year of the slip. Pin / screw penetration of the cartilage has been implicated as a possible cause but it occasionally occurs without surgical intervention. Radiographs show a narrowed joint space associated with osteoporosis and subchondral erosions.

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Fig.1

Frog lateral radiograph of the pelvis demonstrating a left slipped capital femoral epiphysis. There is loss of normal alignment of the femoral head relative to the proximal femoral metaphysis.
Slipped capital femoral epiphysis, Fig.1
Slipped capital femoral epiphysis, Fig.2
Slipped capital femoral epiphysis, Fig.3