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- See:
      - Medial Collateral Ligament:
      - Varus Stress Test:

- Primary vs Secondary Restraints:
     - seationing of MCL results in marked valgus instability;
     - isolated sectioning of ACL, PCL, LCL, or posterolateral structures does not cause large increases in valgus angulation;
    - cutting of MCL + PCL results in more instability than any other combination;
            - hence, primary restraint to valgus rotation is MCL, w/ PCL playing a secondary role.

- Flexion Instability:
    - when tested in flexion which relaxes posterior capsule, same liga-mentous 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;
    - medial capsular layers provide stability to valgus stresses at knee & are primary stabilizer at 30 deg of flexion, (and 0 deg);

- Extension Instability:
    - intact cruciate ligaments and posterior capsule are taut & little abduction or adduction instability is detectable;
    - MCL is more a secondary medial stabilizer in full extension;
    - at full extension, MCL resists about 50% of applied valgus moment, whereas anterior & posterior aspects of capsule resist about 25 %;
    - ACL & PCL together resist about 25% of applied force (PCL > ACL);
    - in full extension ACL is a primary stabilizer w/ contribution from the posteromedial capsule;
    - secondary restraints:
          - MCL is more a secondary medial stabilizer in full extension;
          - deep medial collateral ligament, medial meniscus, & anterior & posterior cruciate ligaments are important 2nd restraints;
    - valgus laxity in hyperextension;
         - instability w/ varus or valgus stress testing suggests cruciate ligament disruption in addition to collateral ligament disruption;
         - indicates disruption of MCL, ACL, posterior oblique ligament, medial portion of posterior capsule & possibly PCL