Mechanism-based pattern approach to classification of complex injuries of the knee depicted at MR imaging

Complex knee injuries are common, often resulting from multiple forces: var us, valgus, hyperextension, hyperflexion, internal rotation, external rotat ion, anterior or posterior translation, and axial load. Certain combination s of forces are known to cause specific injury patterns. After a review of the literature, th e authors developed a mechanism-based classification sys tem based on patterns of bone marrow edema and ligament injury for complex knee injuries depicted at magnetic resonance imaging. The classification sy stem takes into account knee position and forces and recognition of pattern s of bone injury and complementary soft-tissue injury. Ten mechanism-based injury patterns were recognized: (a) pure hyperextension, (b) hyperextensio n with varus, (c) hyperextension with valgus, (d) pure valgus, (e) pure var us, (f) flexion with valgus and external rotation, (g) flexion with varus a nd internal rotation, (h) flexion with posterior tibial translation, (i) pa tellar dislocation (flexion, valgus, and internal rotation of femur on fixe d tibia), and (j) direct trauma. Recognition of these patterns may help ass ess the full extent of knee injury, particularly at the posterolateral and posteromedial corners of the knee.