Valgus/Varus Stress Test for the knee: how to assess the collateral ligaments

When a knee takes a hit from the side, or gets forced inward or outward abruptly (a very typical mechanism in contact sports or changes of direction), the first suspects are usually the collateral ligaments: the medial (MCL) and the lateral (LCL). The valgus/varus stress test is the most direct way to assess them.

What does this test measure?

This test assesses the stability of the collateral ligaments by applying a force that opens the joint to one side:

• Valgus stress (forcing the knee inward) loads the medial collateral ligament (MCL)
• Varus stress (forcing the knee outward) loads the lateral collateral ligament (LCL)

It's performed both in full extension and with the knee flexed to 30°, because each position gives different information about which structures are involved.

Equipment needed

• A treatment table
• No additional tools

Protocol

1. At 30° of flexion (mainly isolates the MCL/LCL)

1. The patient lies face-up, with the knee flexed about 30° (you can support it on your thigh or a cushion)
2. For valgus (MCL): place one hand on the lateral side of the knee as a pivot point, and the other on the medial side of the ankle, applying a force that opens the knee inward
3. For varus (LCL): reverse your hands, applying a force that opens the knee outward
4. Assess the joint line opening and end-feel, comparing with the healthy side

2. In full extension (also assesses capsular structures and the cruciates as secondary stabilizers)

1. Repeat the same maneuvers (valgus and varus) with the knee in full extension
2. Significant opening in extension suggests a more severe or combined injury (not just the collateral ligament, but also capsular/cruciate structures)

Common mistakes

• Not testing both positions (30° and full extension), which provide complementary information
• Applying force abruptly, causing unnecessary pain
• Not comparing with the opposite knee to establish that person's "normal"

How to interpret the result

Result	Interpretation
Opening only in valgus at 30°, no opening in extension	Suggests an isolated MCL injury, mild to moderate grade
Opening in valgus both at 30° and in extension	Suggests a more severe MCL injury or involvement of additional structures (possible associated ACL injury)
Opening in varus at 30°, no opening in extension	Suggests an isolated LCL injury, mild to moderate grade
Opening in varus both at 30° and in extension	Suggests a more severe LCL injury, possible involvement of posterolateral structures

Collateral ligament injuries are typically graded I-III based on the amount of opening and the end-feel. Grade III injuries (with marked opening and a soft end-feel) usually require specialized medical assessment, especially if there's suspected combined involvement with the ACL or PCL.

Relationship with other tests

The valgus/varus stress test pairs especially well with:

• Lachman test — to rule out combined ACL involvement when there's opening in extension
• Posterior drawer test — to rule out PCL involvement in complex injuries

Track ligament laxity over time

In collateral ligament injuries managed conservatively (the most common approach for grade I-II), tracking the amount of opening and pain over the weeks helps decide when to progress the load. In Movalytics you can log the result of the valgus/varus stress test alongside the rest of the knee assessment, and compare how it progresses with each check-in.

FAQ

What's the difference between testing at 30° and in extension? At 30° you better isolate the corresponding collateral ligament. In full extension, other structures (capsule, cruciates) also contribute to stability, so opening in extension usually indicates a more extensive injury. Do collateral ligament injuries always require surgery? No, most grade I-II MCL injuries are treated conservatively with good results. Grade III injuries, or those combined with other structures (especially the LCL and posterolateral structures), are more likely to require surgical evaluation. Does this test hurt a lot? It can cause discomfort, especially in the acute phase, so it should be applied with control and after clearly explaining to the patient what's about to happen.