Traumatic Bone Bruises in the Athlete’s Knee

CONTEXT: Mobile water within the bone marrow is a physiological phenomenon that is identifiable on magnetic resonance (MR) imaging, and signal changes can result from blood pooling, reactive hyperemia, edema, and microfracture. When these MR lesions are associated with an acute traumatic event, the findings are referred to as bone bruises and so represent a unique manifestation of injury. This review discusses bone bruises in anterior cruciate ligament (ACL) tears, patella dislocations, occult fractures, and contusions. METHODS: A PubMed search of the literature from 1982 to December 2009 was conducted with the terms knee and bone bruise. RESULTS: Bone bruises are associated with ACL tears, patella dislocations, occult fractures, and contusions. For each injury, a unique pattern of bone bruising is found on MR imaging, which results from the acute trauma. When acute trauma produces a subchondral lesion with low T1-weighted and high T2-weighted signal intensity, the resulting bony contusion is best described as a bone bruise. CONCLUSIONS: Bone marrow edema is identified using MR imaging and may result from traumatic or atraumatic causes. Bone bruises can be characterized by their pattern at presentation, by the mechanism of injury, and by their associated injuries. This type of bone edema can accompany contact and noncontact ACL ruptures as well as patella dislocations. Although increased marrow edema can be associated with an occult fracture, the long-term significance of these lesions is unclear.