Knee Orthopaedic Test: Varus Stress Test

The Varus Stress Test is a knee special test used to assess lateral knee response when a varus force is applied to the tibiofemoral joint. It is most commonly used to support assessment reasoning around lateral collateral ligament involvement and, in some cases, broader posterolateral corner involvement.

A positive finding may include familiar lateral knee pain, increased lateral joint opening, or a softer end-feel compared with the other side. However, diagnostic accuracy evidence for the Varus Stress Test is limited, and the test should not be used as a stand-alone diagnostic tool.

Introduction

The Varus Stress Test is a manual knee assessment used to observe the lateral knee’s response to varus loading. It is commonly associated with the lateral collateral ligament, also called the LCL.

The LCL helps resist varus stress at the knee. Testing at approximately 20–30 degrees of knee flexion is commonly used to place more emphasis on the LCL, while testing in full extension may provide information about broader lateral, capsular, cruciate or posterolateral corner involvement.

The test may be relevant after a direct blow to the inside of the knee, a varus force mechanism, pivoting injury, hyperextension-type trauma or sport collision. However, isolated LCL injuries are less common than many other knee injuries, and lateral knee instability may involve multiple structures.

A positive Varus Stress Test may increase suspicion of lateral knee ligament involvement when it matches the history and other findings. It does not confirm an LCL injury. A negative finding does not fully exclude lateral or posterolateral knee injury.

Quick Summary

Test name: Varus Stress Test
Region: Knee
Primary structure assessed: Lateral collateral ligament and lateral knee structures
Common use: Lateral knee pain or suspected LCL/posterolateral involvement after trauma
Positive finding: Lateral knee pain, increased lateral joint opening, or softer end-feel compared with the other side
Negative finding: No relevant pain, no meaningful side-to-side laxity and firm end-feel
Common angles: Approximately 20–30 degrees knee flexion and full extension
Main limitation: Diagnostic accuracy evidence is limited and should be interpreted cautiously.

What Is the Varus Stress Test?

The Varus Stress Test is a manual knee assessment where the professional applies a varus force to the knee. In practical terms, the lower leg is moved inward relative to the thigh, creating stress through the lateral side of the knee.

The test is usually performed in two positions:

At approximately 20–30 degrees of knee flexion
This position is commonly used to assess the LCL more specifically.

In full knee extension
This position may suggest broader lateral, capsular, cruciate or posterolateral corner involvement if increased opening is present.

The professional observes and records pain, gapping, end-feel, side-to-side difference and symptom reproduction.

Why It Is Used

The Varus Stress Test may be used to support assessment reasoning around:

• Lateral knee pain after trauma
• Suspected LCL involvement
• Possible posterolateral corner involvement
• Varus or hyperextension injury mechanism
• Direct blow to the inside of the knee
• Side-to-side knee laxity comparison
• Instability symptoms
• Sport collision or twisting injuries
• Whether further assessment may be appropriate

The test is useful because it is quick and clinically familiar. It is strongest when combined with history, palpation, swelling, range of motion, other ligament tests and functional assessment.

What It Assesses

The Varus Stress Test assesses the knee’s response to varus loading.

It may provide information about:

• Lateral knee pain response
• Lateral joint opening
• End-feel quality
• Side-to-side laxity difference
• LCL-related assessment reasoning
• Possible posterolateral corner involvement
• Irritability under varus load

It does not directly assess:

• LCL fibre integrity with certainty
• Posterolateral corner structure integrity with certainty
• MRI findings
• Meniscus status
• ACL or PCL integrity
• Strength
• Running capacity
• Readiness for sport or work
• Tissue healing
• Functional performance

Who It Is Useful For

The test may be useful for clients with:

• Lateral knee pain after trauma
• A varus or hyperextension mechanism
• A direct blow to the inside of the knee
• A feeling of lateral knee instability
• Sport-related knee injury
• Difficulty with pivoting, cutting or landing
• Lateral knee symptoms during load-bearing tasks
• A need for baseline or retest documentation in Measurz

It may also be useful for professionals learning how to structure lateral knee assessment.

When to Use This Test

Consider the Varus Stress Test when:

• The injury mechanism suggests varus stress
• The client reports lateral knee pain after trauma
• LCL or posterolateral involvement is part of the assessment reasoning
• You want to compare lateral laxity side to side
• You need to document pain and end-feel under varus load
• You are building a broader knee ligament assessment profile

It should usually be combined with other tests for ACL, PCL, posterolateral corner, meniscus, range of motion and functional performance where appropriate.

When Not to Use or When to Be Cautious

Use caution or avoid the test when:

• There is suspected fracture
• The knee is highly irritable or acutely swollen
• The client cannot relax the limb
• The client cannot tolerate manual stress
• There is severe pain before testing
• There are neurological symptoms
• There is a major deformity or inability to bear weight after trauma
• The professional is not confident the test can be performed safely

Stop the test if pain increases sharply, the client becomes distressed, the knee feels grossly unstable in a concerning way, or the client asks to stop.

Equipment Required

The Varus Stress Test usually requires no equipment.

Optional equipment includes:

• Measurz app
• Pain rating scale
• Treatment table or plinth
• Towel roll or bolster
• Video recording for education or comparison
• Notes field for angle, pain, laxity and end-feel
• Instrumented laxity or stress-imaging tools in specialist settings

Step-by-Step Protocol / Practice

Setup

Ask the client to lie supine on a plinth or firm surface.

Expose the knee enough to observe alignment, swelling and movement. Make sure the client is comfortable and relaxed.

Test the unaffected or less symptomatic side first where appropriate to understand the client’s normal end-feel.

Client position

The client lies supine with the tested knee relaxed.

For the 20–30-degree test:

• Hip relaxed
• Knee flexed to approximately 20–30 degrees
• Lower leg supported
• Foot and ankle relaxed

For the extension test:

• Knee close to full extension
• Limb relaxed
• Avoid forced locking or hyperextension

Examiner/professional position

The professional stands on the side of the tested leg.

One hand stabilises the medial side of the distal femur or knee region. The other hand controls the ankle or distal tibia.

Hand placement

For a right knee example:

• Place one hand on the medial aspect of the knee or distal femur to stabilise.
• Place the other hand around the distal tibia or ankle.
• Keep the client’s limb relaxed.

Stabilisation

Stabilise the thigh so the force is applied through the knee rather than rotating the whole limb.

The pelvis and hip should remain relaxed and neutral.

Movement or force direction

Apply a varus force to the knee.

This means the distal tibia is gently moved medially while the knee is stabilised, stressing the lateral side of the knee.

Apply the force gradually and compare with the opposite side.

Instructions

Tell the client:

“Stay relaxed and let me move your leg. I am going to apply a gentle stress to the outside of the knee. Tell me if this reproduces your familiar symptoms and where you feel it.”

Positive finding

A positive finding may include:

• Familiar lateral knee pain
• Increased lateral joint opening compared with the other side
• Softer or less distinct end-feel
• Apprehension or symptom reproduction
• Greater laxity at 20–30 degrees
• Greater laxity in full extension suggesting broader involvement

Record whether the positive finding was based on pain, laxity, end-feel or a combination.

Negative finding

A negative finding may include:

• No relevant lateral knee pain
• No meaningful side-to-side laxity difference
• Firm end-feel
• No familiar symptom reproduction
• Similar response to the opposite side

A negative finding does not fully exclude lateral knee injury.

Stopping criteria

Stop the test if:

• Pain increases sharply
• The client asks to stop
• The client cannot relax
• The knee feels grossly unstable
• The professional cannot control the movement
• The client experiences neurological symptoms
• The test is not safe or meaningful

Safety notes

Use a gradual and controlled force. Do not bounce, jerk or force the knee. Acute knee injuries may be painful and guarded, so interpretation may be limited in early assessment.

Positive and Negative Test Interpretation

A positive Varus Stress Test may increase suspicion of LCL or lateral knee structure involvement when it matches the client’s history, mechanism of injury and lateral knee symptoms. Pain without laxity may suggest a pain-dominant lateral knee response, while clear gapping or a softer end-feel may increase suspicion of structural laxity.

Increased opening at approximately 20–30 degrees may be more suggestive of LCL involvement. Increased opening in full extension may raise concern for broader involvement, including posterolateral, capsular or cruciate structures, but this must be interpreted cautiously.

A positive test does not confirm an LCL injury or posterolateral corner injury. Pain, guarding, swelling and other lateral knee structures may influence the finding.

A negative Varus Stress Test may reduce suspicion of clear lateral laxity, especially when history, palpation, swelling and functional assessment are also reassuring. However, it does not fully exclude lateral or posterolateral knee injury.

The finding is more meaningful when combined with:

• Mechanism of injury
• Lateral knee pain location
• Swelling
• Palpation findings
• Range of motion
• Other ligament tests
• Posterolateral corner assessment
• Gait and movement assessment
• Functional testing
• Imaging where relevant

Sensitivity, Specificity and Diagnostic Accuracy

High-quality diagnostic accuracy evidence for the Varus Stress Test appears limited.

One commonly cited study by Harilainen reported low sensitivity for the Varus Stress Test, around 25%, and specificity was not clearly reported in some summaries. This suggests that a negative manual Varus Stress Test should not be used on its own to exclude lateral collateral ligament involvement.

Condition or presentation: Acute knee ligament injury
Population: Acute knee ligament injury sample
Test variation: Varus stress testing for lateral ligament involvement
Reference standard: Compared with stress radiography, examination under anaesthesia, arthroscopic or operative findings in the broader study context
Sensitivity: Approximately 25% in commonly cited summaries
Specificity: Not clearly available in commonly cited summaries
Positive likelihood ratio: Not clearly available
Negative likelihood ratio: Not clearly available
Key limitation: Evidence is older, limited, and not sufficient for confident stand-alone interpretation.

Plain-language interpretation:

• A positive result may increase suspicion if it matches the mechanism and other findings.
• A negative result does not confidently exclude LCL or posterolateral involvement.
• The test should be combined with broader knee assessment.
• If symptoms, mechanism or functional instability remain concerning, further assessment may still be appropriate.

Reliability and Validity

The Varus Stress Test has clinical face validity because it applies varus load to the knee and allows the professional to assess lateral pain, gapping and end-feel.

Reliability may be affected by:

• Examiner experience
• Acute pain and guarding
• Knee flexion angle
• Force magnitude
• Hand placement
• Client relaxation
• Whether pain or laxity is used as the main positive finding
• Difficulty detecting subtle lateral gapping manually

Validity as a stand-alone diagnostic test is limited. The test is more useful when combined with mechanism of injury, palpation, other ligament tests, posterolateral corner tests, movement assessment and imaging where relevant.

Instrumented stress methods or imaging may quantify lateral gapping more objectively in specialist settings, but manual testing remains a practical screening and assessment-reasoning tool.

Common Errors and Limitations

Common errors include:

• Testing only one angle
• Applying force too aggressively
• Not comparing with the opposite side
• Not recording whether pain or laxity was positive
• Ignoring end-feel quality
• Testing while the client is guarding
• Assuming pain means LCL injury
• Assuming no laxity excludes LCL injury
• Not assessing posterolateral corner involvement
• Calling the test diagnostic

Limitations include:

• Diagnostic accuracy evidence is limited
• Manual force is difficult to standardise
• Subtle laxity can be missed
• Pain and swelling can limit assessment
• Isolated LCL injury may be uncommon
• Combined injuries may alter findings
• A single test should not guide decisions alone

Practical Applications

The Varus Stress Test may be useful for:

• Lateral knee assessment
• LCL-related assessment reasoning
• Posterolateral corner screening context
• Side-to-side laxity comparison
• Baseline documentation
• Retesting over time
• Deciding whether further assessment may be needed
• Communicating findings to clients
• Supporting Measurz knee assessment reports

It is best used as part of a broader assessment that includes history, swelling, range of motion, palpation, gait, functional tasks and other ligament tests.

How to Record This in Measurz

Record:

• Test name: Varus Stress Test
• Side tested
• Knee angle: 20–30 degrees or full extension
• Result: positive, negative, unclear or unable to test
• Pain score
• Symptom location
• Pain quality
• Laxity: none, mild, moderate or marked
• End-feel: firm, soft or absent
• Comparison side
• Mechanism of injury
• Irritability
• Guarding or compensations
• Reason for stopping if relevant
• Related findings
• Confidence in result
• Further assessment or referral notes if appropriate
• Retest date if relevant

Recording these details improves repeatability, communication, client education, assessment reasoning, monitoring over time, team consistency and reporting quality.

Related Tests / Internal Links

• Valgus Stress Test
• Lachman Test
• Anterior Drawer Test
• Posterior Drawer Test
• Dial Test
• Posterolateral Drawer Test
• McMurray Test
• Thessaly Test
• Knee Girth
• Knee Range of Motion
• Hop testing
• Balance testing

FAQs

What does the Varus Stress Test assess?

It assesses the knee’s response to varus load and is commonly used to support reasoning around LCL or lateral knee involvement.

What is a positive Varus Stress Test?

A positive finding may include lateral knee pain, increased lateral joint opening or a softer end-feel compared with the other side.

Should the test be done at 20–30 degrees or full extension?

Both may be useful. The flexed position is commonly used for LCL emphasis. Full extension may provide information about broader stabilising structures.

Does a positive test diagnose an LCL injury?

No. It may increase suspicion, but it does not confirm injury on its own.

Does a negative test exclude an LCL injury?

No. Diagnostic accuracy evidence is limited, so a negative result does not fully exclude lateral knee involvement.

Should posterolateral corner tests also be used?

Yes, where relevant and within scope, especially if the mechanism or symptoms suggest broader lateral or posterolateral involvement.

Is the test useful after acute injury?

It can be useful, but acute pain, swelling and guarding may limit interpretation.

What should the test be combined with?

History, mechanism, palpation, swelling, range of motion, other ligament tests, gait and functional assessment.

Key Takeaways

The Varus Stress Test is commonly used to assess lateral knee response to varus load.

Testing at 20–30 degrees and full extension provides different information.

Positive findings may include pain, gapping or altered end-feel.

Diagnostic accuracy evidence is limited, and the test should be interpreted cautiously.

A negative test does not confidently exclude LCL or posterolateral involvement.

Measurz recording should include angle, pain, laxity, end-feel and side-to-side comparison.

References

Harilainen, A., Myllynen, P., & Antila, H. (1986). Diagnosis of acute knee ligament injuries: The value of stress radiography compared with clinical examination, stability under anesthesia and arthroscopic or operative findings. Annales Chirurgiae et Gynaecologiae, 75, 37–43.

Harilainen, A. (1987). Evaluation of knee instability in acute ligamentous injuries. Annales Chirurgiae et Gynaecologiae, 76, 269–273.

Logerstedt, D. S., Scalzitti, D. A., Risberg, M. A., Engebretsen, L., Webster, K. E., Feller, J., Snyder-Mackler, L., & Axe, M. J. (2017). Knee stability and movement coordination impairments: Knee ligament sprain revision 2017. Journal of Orthopaedic & Sports Physical Therapy, 47(11), A1–A47. doi:10.2519/jospt.2017.0303

NICE. (2024). Knee pain — assessment: Examination. National Institute for Health and Care Excellence Clinical Knowledge Summaries.

Smith, T. O., Davies, L., & Hing, C. B. (2016). A systematic review to determine the reliability of knee joint clinical assessment tests. The Knee, 23(2), 219–228. doi:10.1016/j.knee.2015.06.010

Terry, G. C., & LaPrade, R. F. (1996). The posterolateral aspect of the knee: Anatomy and surgical approach. The American Journal of Sports Medicine, 24(6), 732–739. doi:10.1177/036354659602400606