- 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;
