The cap sign is seen on ultrasound in the setting of a cortical step-off and suggests the presence of a fracture. It consists of a hyperechoic line (indicated by arrow) that appears on transverse ultrasound view (B) just above the curvilinear-appearing hyperechoic cortex. The sagittal view (A) of the same metatarsal fracture shows a cortical step-off and edema (dashed arrow) superficial to it.
