Bone contusions of the posterior lip of the medial tibial plateau (contrecoup injury) and associated internal derangements of the knee at MR imaging

PURPOSE: To determine if there are any predictable patterns of internal der angement associated with a bone contusion of the posterior lip of the media l tibial plateau at magnetic resonance (MR) imaging and to offer a biomecha nical explanation for the findings. MATERIALS AND METHODS: A retrospective review of 215 consecutive MR examina tions for knee trauma was conducted to identify contusions of the posterior lip of the medial tibial plateau. Any additional contusions and internal d erangements were documented in the cases With these contusions. Medical cha rts and arthroscopic results, when available, were reviewed for mechanisms of injury. RESULTS: The specific medial tibial contusion was demonstrated in 25 of 215 (12%) knee MR examinations. Associated anterior cruciate ligament (ACL) te ars were found in 25 of the 25 (100%) examinations. Injury to the meniscoca psular junction (14 of 25) or;a peripheral tear of the posterior horn of th e medial meniscus (10 of 25) occurred in a combined 96% of the cases. Later al compartment contusions were noted in 24 (96%) cases. Pivot, twisting, or valgus forces were reported mechanisms of injury. CONCLUSION: Contusions involving the posterior lip of the medial tibial pla teau may result from a contrecoup impaction injury directly following an AC L tear, as the knee reduces. These contusions are almost always associated with a far peripheral meniscal tear or with a meniscocapsular junction inju ry affecting the posterior horn of the medial meniscus.