Pivot Shift Injury

Source:  Pivot Shift Injury    Tag:  dunn view radiograph
A pivot shift injury occurs when a valgus force is applied to the knee in combination with external rotation of the tibia or internal rotation of the femur. Pivot shift injuries are most commonly seen in skiers and American football players.

The injury occurs when there is rapid deceleration with simultaneous direction change, which loads the anterior cruciate ligament (ACL), sometimes to the point of rupture (red arrow). With rupture of the anterior cruciate ligament, there is anterior subluxation of the tibia relative to the femur, which causes impaction of the lateral femoral condyle against the posterolateral margin of the lateral tibial plateau.

MRI will show marrow signal abnormality with or without osteochondral injuries in the posterior aspect of the lateral tibial plateau (green arrows) and the midportion of the lateral femoral condyle (blue arrows) near the lateral condylopatellar sulcus (lateral femoral notch). The posterior lip of the medial tibial plateau can also be involved, likely from contrecoup forces at resolution of the valgus load.

The location of the lateral femoral condyle injury depends on the degree of flexion of the knee at the time of injury: More flexed positions during injury result in more posteriorly located bone contusions, while Less flexed positions during injury result in more anteriorly located contusions.

Soft tissue injuries seen on MRI include disruption of the anterior cruciate ligament, most commonly in its midsubstance followed by near the femoral attachment site; tears of the posterior capsule and arcuate ligament; tears of the posterior horns of the lateral or medial menisci; and a tear of the medial collateral ligament (MCL).

References

Sanders TG, Medynski MA, Feller JF, Lawhorn KW. Bone contusion patterns of the knee at MR imaging: footprint of the mechanism of injury. Radiographics. 2000 Oct;20 Spec No:S135-51.