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Varus Stress Test

- See:
      - Valgus Stress Test:
      - Lateral Collateral Ligament:

- Torn Collateral Tested in Flexion:
    - when tested in flexion which relaxes posterior capsule, same ligamentous laxity will result in a much greater degree of instability;
    - at 30 deg flexion, the cruciates are in their most relaxed state, and pathologic laxity palpated is capsular laxity;
    - varus instability in flexion:
          - role of LCL increases w/ joint flexion, as posterolateral structures become lax;
          - w/ joint flexion, resistance by ACL decreases, but large forces are found in PCL at 90 degrees of flexion;
          - LCL is primary restraint to varus stress at 5 deg & 25 deg flexion;
          - lateral capsular structure provide secondary support;
          - iliotibial band & popliteus muscles have dynamic stabilizing role;

- Torn Collateral Tested in Extension:
    - intact cruciate ligaments and posterior capsule are taut & little abduction or adduction instability is detectable;
    - instability w/ varus or valgus stress testing suggests cruciate ligament disruption in addition to collateral ligament disruption;
    - varus laxity in hyperextension;
           - instability to varus angulation indicates damage to arcuate complex & PCL;
           - cruciate ligaments (primarily ACL) resist approx 25% of moment at full extension;

- One Plane Lateral Instability:
    - one plane lateral instability is apparent on varus stress testing when knee opens on the lateral side;
    - indicates disruption of lateral capsular ligament, LCL, biceps tendon, iliotibial band, arcuate & popliteus complex, PCL, and possibly the 
           ACL (this is major instability approaching severity of disloation);

- Postero-Lateral Instability:
    - expect to find increased varus rotation and external rotation at 30 deg of knee flexion;
    - similarly, the same knee flexed to 90 deg will demonstrate decreased varus and external rotaion moments;
    - in contrast, when there is increased varus rotation and external rotation moments at both 30 and 90 deg of flexion, then there are tears of 
           the PCL and posterolateral corner

Limits of movement in the human knee. Effect of sectioning the posterior cruciate ligament and posterolateral structures.