Knee Valgus Test: Purpose, Technique, Positive Signs & Grading
What Is the Knee Valgus Test Used For?
The knee valgus test, also called the valgus stress test, is an orthopedic special test that checks the integrity of the medial collateral ligament (MCL). The MCL is a broad band of tissue on the inner side of the knee that connects the femur to the tibia. It is the main restraint against forces that push the knee inward, and it is one of the most commonly injured ligaments in sports such as football, skiing, soccer, and basketball.
Clinicians use the test after a knee injury, especially when a patient reports a blow to the outer knee or a twisting injury, to decide whether the MCL is sprained, partially torn, or completely torn.
How to Perform the Knee Valgus Test
The test is quick and needs no equipment, but it should be done by a trained clinician. The standard technique is:
- Position the patient supine (lying on their back) with the leg relaxed.
- Place the affected leg in extension with slight external rotation.
- Stabilize the limb. One hand holds the medial ankle (near the medial malleolus), and the other hand supports the lateral side of the knee.
- Apply a medially directed stress to the lateral knee. This pushes the knee into valgus (inward) while the ankle is held steady.
The clinician watches for pain and compares how far the inner joint space opens with the uninjured knee. Comparing sides matters, because normal ligament laxity varies from person to person. As described in Orthofixar’s valgus stress test guide, the test is often repeated with the knee in slight flexion (around 20–30 degrees), where the MCL is isolated more.
What Is a Positive Result?
A positive sign is pain, hypermobility (excessive opening), or both at the medial aspect of the knee compared with the opposite side. Pain without much opening usually suggests a lower-grade sprain. Marked opening with a soft or absent endpoint suggests a more severe tear.
Grading MCL Laxity
The varus and valgus stress tests are graded by how much the joint space opens compared with the other knee:
| Grade | Findings |
|---|---|
| Grade I | Joint space opens within 2 mm of the opposite side |
| Grade II | Opens 3–5 mm more than the opposite side at 20° of flexion, and less than 2 mm more than the normal knee in full extension |
| Grade III | Opens 5–10 mm more than the normal knee at both 20° of flexion and full extension |
Higher grades mean more ligament damage. Laxity in full extension in particular can suggest that other structures, such as the posterior oblique ligament or cruciate ligaments, are also injured. This is why a thorough knee exam doesn’t rely on a single test.
Why the Test Matters Clinically
Accurate MCL assessment guides treatment. Many isolated Grade I and II injuries heal well with protection, bracing, and structured rehabilitation. Grade III injuries, or MCL tears combined with other ligament damage, may need further imaging such as MRI and sometimes surgical consultation. Special tests like the valgus stress test help clinicians decide who needs imaging and how urgently.
Limitations to Keep in Mind
- Pain and muscle guarding can limit the exam, especially right after injury.
- Results should be interpreted alongside the history, swelling, tenderness over the ligament, and other knee tests.
- Imaging may be needed to confirm the diagnosis, particularly when several structures could be involved.
This article is for educational purposes and isn’t a substitute for professional medical advice. If you suspect a knee ligament injury, see a qualified healthcare professional.
Frequently Asked Questions (FAQ)
What does the knee valgus test check?
It checks the integrity of the medial collateral ligament (MCL) on the inner side of the knee.
What position is the patient in during the test?
The patient lies supine, with the affected leg extended and slightly externally rotated.
What does a positive knee valgus test mean?
A positive test shows pain and/or excessive opening at the medial knee compared with the uninjured side, suggesting an MCL sprain or tear.
How is the valgus stress test graded?
It is graded I to III according to how much the medial joint space opens compared with the opposite knee, from within 2 mm (Grade I) up to 5–10 mm (Grade III).
Is the knee valgus test painful?
It can be uncomfortable, particularly with an acute injury, but it should be done gently and stopped if pain is severe.
Can the valgus stress test diagnose an MCL tear on its own?
No. It is an important screening tool, but diagnosis also relies on history, physical findings, and sometimes MRI.
What is the difference between the valgus and varus stress tests?
The valgus test stresses the inner knee (MCL), while the varus test stresses the outer knee (lateral collateral ligament).
Can an MCL injury heal without surgery?
Many isolated MCL injuries, particularly Grades I and II, heal with conservative care. A clinician should decide this after proper assessment.
References
- Clinical Tests for the Musculoskeletal System, Third Edition.
- Dutton M. Dutton’s Orthopaedic Examination, Evaluation, and Intervention, 3rd Edition.
- Smith BW, Green GA. Acute knee injuries: part I. History and physical examination. Am Fam Physician. 1995;51:617.
- Valgus stress test of the knee, Orthofixar
- PubMed search: valgus stress test and medial collateral ligament