Orthopedic surgeons know that kids don’t always read the script when it comes to injury exams. Ask a 7-year-old with a supracondylar humerus fracture to wiggle their fingers, and you might get a shrug, a giggle, or a tearful “no.” Meanwhile, lurking beneath the cast of cartoons on their T-shirt could be a hidden nerve injury you’d really like to catch before heading to the OR.
A new study out of Fukuoka, Japan, just gave us another arrow in the diagnostic quiver — something called the “Blurred Boundary” (BB) sign. Published August 15, 2025, in JBJS Open Access, the research suggests that a fuzzy-looking muscle–fat interface on a lateral elbow X-ray could be the radiographic red flag for nerve damage in extension-type supracondylar humeral fractures.
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