A 6-year-old child is brought to the emergency department with a supracondylar fracture of the humerus. Clinically, the child has a palpable but diminished radial pulse, normal hand colour, and normal capillary refill time. A second child with a similar fracture has an absent radial pulse, pale hand, delayed capillary refill (>3 seconds), and cold fingers. Which finding best distinguishes a fracture with brachial artery *compression* from one with brachial artery *injury*?