Procedure
- The patient lies in supine position with extended knees and hips.
- Stand on the side of the leg to be tested.
- Place the upper leg diagonally across the examination table, so that the knee can be flexed by 20-30°.
- The posterior capsule and the cruciate ligaments will be relaxed.
- Stabilise the upper leg by positioning one hand on the vastus lateralis muscle above the knee.
- With the other hand, apply a valgus-inducing force on the lower leg [Figure 78].
- This tests the laxity of the medial collateral ligament and compresses the lateral meniscus.
Figure 78
- Stabilise the upper leg by placing a hand on the vastus medialis muscle above the knee.
- With the other hand, apply a varus-inducing force on the lower leg [Figure 79].
- This tests the laxity of the lateral collateral ligament and compresses the medial meniscus.
Figure 79
- Repeat the tests with a fully extended knee to test the dorsal knee structures (posterior capsule & posterior cruciate ligament).
- During each test, note:
- Abnormal mobility.
- Indication of pain; meniscal damage, ligament damage.
- Muscular defence.
- Blockage (meniscal damage on the compression side).
- Left-right differences.
In the case of abnormal mobility with 20-30° flexion, the knee is unstable and a rupture of the collateral ligament should be considered.
If abnormal mobility also occurs with a fully extended knee, damage to the posterior cruciate ligament and the posterior capsule is likely.
The knee is normally most stable in the extended position. If there is an isolated collateral ligament injury, then valgus or varus stress reveals no abnormalities in this position (in the case of an intact posterior capsule and posterior cruciate ligament).