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Have you missed a fracture associated with an ACL injury? Plain radiography generally fails to detect subchondral fractures around the knee associated with ACL tears.1 However, those fractures are frequently seen on MRI in patients with acute ACL tear.
When radiologists report ‘fractures’ based on MRI findings, they refer to a very different entity than bone bruises, traumatic bone marrow oedema or contusion, which all refer to an identical image finding—an ill-defined signal alteration without definite evidence of a fracture line. On MRI, a fracture is defined as a dark (low signal intensity) line on the different pulse sequences acquired, commonly surrounded by bone marrow oedema. These ‘dark lines’ are usually better depicted using T1-weighted image without fat suppression (figure 1). When using MRI to assess the knee, such fractures are present in as many as 60%–72% of knees after an acute ACL tear.2 3
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Competing interests None declared.
Provenance and peer review Not commissioned; internally peer reviewed.