Saturday, September 24, 2011

Implication of anterior drawer test, Lachman’s test, Pivot shift test to that of knee Instability

Lachman's vs. Anterior Draw Test

•    Lachman's test may be more difficult for clinicians to perform but tends to be more sensitive
•    In the anterior draw test knee is positioned so that the hamstrings have a mechanical advantage. Increased hamstring activity can inhibit tibial translation, causing a false negative test
•    A torn meniscus can act as a block to tibial motion, again causing a false negative while doing the anterior draw test

Anterior drawer test with tibia external rotation:

Anterior drawer test with tibia in neutral rotation demonstrates equal displacement of both condyles & this displacement is eliminated by internal rotation of the tibia, then both anteromedial and anterolateral rotary instability may be present.

Similarly 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.

Pivot shift test is the test which indicates antrolateral instability (ALI) of the knee.

Research indicates antrolateral instability further increase with injury to LCL (lateral collateral ligament) & PCL (Posterior Cruciate ligament).  Broadly speaking ALI is also associated with injury to accuate complex that includes posterior 1/3 of lateral supporting structures i.e. LCL, arcuate ligament, & exension of popliteus.

It is also reminded to the reader that posterior 1/3 of the lateral ligamentous complex is reinforced by biceps, popliteus, & lateral head of gastrocnemius.

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