Does lateral knee geometry influence bone bruise patterns after anterior cruciate ligament injury? A report of two cases.

Bone bruise patterns are commonly seen after acute anterior cruciate ligament injuries; they represent a subchondral impaction injury that occurs in the lateral knee joint between the mid-lateral femoral condyle and the posterior lateral tibial plateau. These contusion patterns are present in the majority of noncontact ACL injuries. These injury patterns vary significantly in severity and this aspect is poorly understood. Edema patterns have gained increased interest in the literature of late; they may indicate the severity of the initial injury. They also may be correlated with the development of subsequent osteochondral defects and osteoarthritis. Given the location of this subchondral injury, it is plausible to assume that the geometry of the lateral femorotibial joint may play a role in ACL injury mechanism and severity of injury. We are reporting two cases of clinically identical ACL injuries. A patient with a flat lateral tibial plateau was noted to have a much larger bone edema pattern than a second patient with the highly convex lateral tibial plateau. This may shed light on the pathomechanics of ACL injury and suggests that an individual with a relatively flat tibial plateau has a stable lateral knee joint. Therefore, we hypothesize that much greater force is required to dislocate a flat and stable lateral femorotibial joint in a pivot shift pattern to produce an ACL injury. The greater force required results in a large bone edema pattern. Conversely, the individual with a relatively short and convex tibial plateau has an inherently unstable lateral joint and relatively smaller amounts of force would be needed to produce the identical injury to the ACL. As less force is required, smaller bone edema patterns result.