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Anterolateral Rotatory Instability

Discussion

  • defined as excessive forward rotation of tibial plateau w/ excessive lateral opening of the joint;
  • there is excessive internal rotation of tibia on femur in flexion;
    • as knee extends, subluxation is reduced by the bony stability, and a jerk is  noted which is basis for the pivot shift test;

disrupted structures


Exam

  • anterior drawer:
    • lateral tibial plateua rotates forward in relation to femur at 90 deg of flexion with excessive lateral opening of the joint;
    • there is then excessive internal rotation of tibia on femur with the knee in flexion;
    • positive anterior drawer test in neutral tibial rotation, that is accentuated when the test is repeated in 30 deg of external rotation and reduced when performed with the tibia in 15 deg of internal rotation indicates anteromedial rotary instability;
    • when anterior drawer test w/ tibia in neutral rotation demonstrates equal displacment of both condyles & this displacment is elminated by internal rotation of the tibia, then both anteromedial and anterolateral rotary instability may be present;
  • pivot shift;
    • as knee comes into extension while wt bearing anterior subluxation of the lateral tibial plateua is dramatic;

Radiographs