Grey cortex sign (stress fracture)

The grey cortex sign was described as an early sign of stress (fatigue) fractures on plain radiographs and refers to subtle ill-definition/lucency of the cortex at the site of microfracture. However, plain radiography is insensitive (~25%, range 15-25%) for the detection of early-stage injuries. CT is much more sensitive for the detection of bone loss that precedes true fracture , however, MRI is the most sensitive/specific modality for the diagnosis of fatigue fractures .