Test of the knee ligaments

1. What may cause an anterior drawer test to be falsely negative?
2. What is the sag test?
3. How does Lachman's test compare to anterior drawer in sensitivity?

Answers:
1. Hemarthrosis, hamstring spasm, meniscal tear, and other structures (posterior capsule) can limit forward movement of tibia.
2. Test for PCL patency. Place patient supine with knee flexed 90 degrees, test is positive if tibia is displaced posteriorly.
3. Lachman's test, in which knee is flexed 15-30 degrees and anterior force is applied to tibia, is more sensitive than anterior drawer.