The Sweep Test, also known as the stroke test or bulge sign, assesses small to moderate knee effusion by moving fluid within the suprapatellar and parapatellar regions. A positive result may indicate increased intra-articular knee fluid, but it does not identify the cause of swelling on its own.

Introduction

Knee swelling can appear after trauma, surgery, overload, irritation, inflammatory conditions or repeated high-load activity.

The Sweep Test is a simple clinical test used to assess whether fluid is present inside the knee joint. It is especially useful for detecting small to moderate effusion that may not be obvious from observation alone.

It is commonly used alongside:

• knee observation
• temperature comparison
• patellar tap / ballotment test
• range of motion testing
• pain assessment
• ligament testing
• meniscal testing
• functional movement assessment
• training load or injury history

The current MAT article describes the Sweep Test as a way to assess small to moderate knee effusion by moving fluid within the suprapatellar and parapatellar regions. A positive finding is a visible wave or bulge of fluid along the knee, but the test does not identify the cause of effusion on its own.  

Quick Summary

• Test name: Sweep Test
• Also known as: Stroke test, bulge test, effusion wave test, knee hydrops test, patella sweep test
• Body region: Knee
• Purpose: Assess for knee joint effusion
• Commonly associated presentation: Knee swelling, post-injury swelling, post-surgical swelling or irritated knee joint
• Positive finding: Visible fluid wave, bulge or refill along the medial knee after sweeping fluid
• Negative finding: No visible wave, bulge or refill
• Best used with: Observation, patellar tap, knee ROM, pain assessment, history and related orthopaedic tests
• Key limitation: Identifies swelling response but does not determine the underlying cause

What Is the Sweep Test?

The Sweep Test is a knee assessment used to identify fluid within the knee joint.

It is commonly called the:

• sweep test
• stroke test
• bulge test
• effusion wave test
• patella sweep test
• knee hydrops test

The test works by moving fluid from one side of the knee to the other. If fluid is present, a visible wave or bulge may appear around the medial aspect of the knee.

The test is most useful for small to moderate effusions. Large effusions may be more obvious visually or may be better assessed with patellar tap / ballotment testing.

Why It Is Used

The Sweep Test may help professionals assess whether the knee has increased intra-articular fluid.

It may help:

• identify small or moderate knee effusion
• compare swelling between knees
• monitor swelling changes over time
• document response after injury or surgery
• guide exercise or loading decisions
• support referral or further assessment where appropriate
• communicate swelling status clearly between team members

A positive Sweep Test does not explain why the knee is swollen. It only supports the presence of joint fluid.

What It Assesses

The Sweep Test assesses visible fluid movement within the knee joint.

It may provide information about:

• presence of knee effusion
• approximate effusion grade
• side-to-side swelling difference
• response to injury or activity
• change over time
• irritability of the knee joint

It does not directly assess:

• ligament integrity
• meniscal injury
• cartilage injury
• fracture
• infection
• inflammatory disease
• exact fluid volume
• readiness to return to sport

Who It Is Useful For

This test may be useful for:

• exercise professionals
• rehabilitation practitioners
• strength and conditioning coaches
• allied health support teams
• performance coaches
• movement assessment professionals
• students learning knee assessment
• professionals using Measurz or MAT for structured assessment recording

It may be relevant for clients with:

• post-injury knee swelling
• post-surgical swelling
• recurring knee effusion
• swelling after training
• swelling after running, jumping or sport
• reduced knee range of motion
• pain or stiffness linked to swelling
• suspected joint irritation

When to Use This Test

Use the Sweep Test when you want to assess whether knee joint effusion may be present.

It may be useful when the client reports:

• swelling after injury
• knee fullness
• stiffness
• reduced knee flexion or extension
• swelling after activity
• swelling after sport
• pain with a feeling of pressure
• recent increase in training load

The test is especially useful when swelling is not obvious but joint effusion is suspected.

When Not to Use or When to Be Cautious

Use caution with:

• suspected fracture
• acute traumatic injury with severe pain
• suspected infection
• hot, red or severely swollen knee
• suspected deep vein thrombosis
• open wounds or skin infection
• recent surgery where contact is painful or restricted
• severe irritability
• strong guarding

Stop testing if:

• pain escalates
• the client feels unsafe
• skin sensitivity prevents contact
• the knee is too tender to touch
• the client asks to stop
• red flags suggest medical review is needed

Equipment Required

• Treatment table or plinth
• Pain scale
• Symptom notes
• Measurz recording workflow
• Optional tape measure or girth measure
• Optional comparison-side notes
• Optional photo or video record if appropriate and consented

Step-by-Step Protocol / Practice

Setup

Position the client lying supine.

The knee should be relaxed and exposed enough to see the patella, suprapatellar pouch and medial/lateral knee borders.

Use appropriate draping and consent.

Client Position

• Client lies on their back
• Knee is relaxed
• Leg is extended or slightly flexed if needed for comfort
• Quadriceps should remain relaxed
• Both knees may be compared

Examiner / Professional Position

• Stand beside the tested knee
• Face the knee so the medial and lateral joint regions are visible
• Use gentle hand contact
• Watch for a visible wave, refill or bulge

Hand Placement

Common method:

• Use one hand to sweep fluid from the medial side of the knee upwards toward the suprapatellar pouch
• Use the other hand to sweep down the lateral side toward the lateral joint line
• Observe whether fluid returns or bulges on the medial side

Some clinicians reverse the sequence depending on the grading system used. The key is to use the same method consistently and record the approach.

Stabilisation

Keep the knee relaxed.

Monitor for:

• quadriceps contraction
• muscle guarding
• skin tension
• discomfort
• movement of the limb
• inconsistent hand pressure

Movement or Force Direction

Use smooth, firm but gentle strokes.

A common sequence is:

• stroke upward along the medial side of the patella toward the suprapatellar pouch
• stroke downward along the lateral side of the patella toward the lateral joint line
• observe the medial side for a fluid wave or bulge

The test should not be painful.

Instructions

Ask the client to:

• keep the leg relaxed
• report pain or tenderness
• avoid tightening the thigh
• tell you if hand pressure is uncomfortable

Example instruction:

“I’m going to gently move fluid around the knee to check for swelling. Try to keep your thigh relaxed and let me know if anything feels painful or uncomfortable.”

Positive Finding

A positive Sweep Test may include:

• visible wave of fluid
• visible bulge along the medial knee
• refill after sweeping
• side-to-side difference
• swelling response that can be graded

A positive result suggests knee effusion may be present.

Negative Finding

A negative finding involves:

• no visible wave
• no medial bulge
• no refill
• no clear side-to-side swelling difference
• no visible response after sweeping

Stopping Criteria

Stop if:

• pain increases
• the knee is too tender
• skin irritation is present
• the client asks to stop
• red flags suggest medical review

Safety Notes

• Use gentle pressure
• Avoid repeated testing if the knee is irritable
• Do not press aggressively into painful tissue
• Consider medical referral if swelling is sudden, severe, hot, red or unexplained
• Record whether swelling was visible, mild, moderate or large

Positive and Negative Test Interpretation

A positive Sweep Test may suggest increased intra-articular knee fluid.

A positive result is more meaningful when it matches:

• visible knee swelling
• stiffness
• reduced range of motion
• history of trauma
• recent surgery
• swelling after activity
• warmth or irritability
• related ligament, meniscal or joint findings

A positive result does not confirm the cause of swelling.

Possible contributors to knee effusion include:

• recent injury
• post-surgical response
• joint irritation
• inflammatory response
• meniscal irritation
• ligament injury
• cartilage irritation
• osteoarthritis flare
• infection or inflammatory disease in red-flag presentations

A negative test may suggest no obvious small-to-moderate effusion at the time of testing.

However, a negative test does not fully exclude:

• very small effusion
• deeper swelling
• swelling outside the joint
• intermittent swelling after activity
• effusion that appears later after loading

Interpretation is stronger when the Sweep Test is combined with history, observation, palpation, knee range of motion, patellar tap, related orthopaedic tests and functional assessment.

Sensitivity, Specificity and Diagnostic Accuracy

The Sweep Test is primarily a clinical swelling assessment rather than a stand-alone diagnostic test for a specific injury or condition.

At the time of writing, high-quality diagnostic accuracy values such as sensitivity, specificity and likelihood ratios for the Sweep Test as a stand-alone diagnostic test for a specific knee pathology appear limited.

This means the Sweep Test should be interpreted as:

• a knee effusion assessment
• a swelling-monitoring tool
• a way to document change over time
• part of broader assessment reasoning

rather than a test that diagnoses the cause of knee swelling.

Practical interpretation:

• A positive test may increase confidence that effusion is present.
• A negative test does not fully exclude small or intermittent effusion.
• The test does not identify whether swelling is caused by ligament, meniscus, cartilage, inflammatory or post-surgical factors.
• Cause of swelling should be considered with history, mechanism, pain, warmth, ROM, function and other findings.

Reliability and Validity

A key post-2000 study by Sturgill, Snyder-Mackler, Manal and Axe assessed the inter-rater reliability of a clinical grading scale for knee joint effusion using a modified stroke test. The study included 75 people aged 16–65 years receiving outpatient physical therapy for unilateral knee problems and reported substantial inter-rater reliability, with kappa reported around 0.64.  

Clinical summaries of that study also report the inter-examiner reliability as κ = 0.64, with confidence interval values around 0.54 to 0.81.  

Reliability improves when the professional uses:

• consistent client position
• consistent hand sequence
• consistent pressure
• consistent grading criteria
• same comparison side
• same time of day where practical
• similar activity state before testing
• clear documentation in Measurz

Reliability may be reduced by:

• inconsistent stroke direction
• excessive or insufficient pressure
• poor lighting
• high body hair or soft tissue variation
• client guarding
• inaccurate grading
• failing to compare sides
• testing immediately after exercise without recording context

Validity is stronger when Sweep Test findings align with:

• visible swelling
• reduced knee range of motion
• joint stiffness
• client report of fullness
• patellar tap findings
• post-activity swelling pattern
• relevant clinical history

The Sweep Test has practical validity for monitoring effusion, but it does not validate the cause of swelling on its own.

Common Errors and Limitations

Common errors include:

• using inconsistent hand direction
• applying too much pressure
• applying too little pressure
• not watching for the fluid wave
• testing through clothing
• not comparing both knees
• not recording grading criteria
• confusing extra-articular swelling with joint effusion
• assuming swelling explains all symptoms
• using the test to diagnose a specific injury

Limitations include:

• does not identify the cause of effusion
• may miss very small or intermittent effusion
• may be less useful with large effusions than patellar tap
• grading can be subjective
• swelling may fluctuate with activity, time and irritability
• skin and soft tissue factors may affect visibility
• requires consistent method for repeat testing

Practical Applications

The Sweep Test may help professionals:

• assess knee effusion
• monitor swelling after injury or surgery
• compare involved and uninvolved knees
• track response to training or loading
• guide exercise progression discussions
• support referral decisions when swelling is unexplained or concerning
• communicate swelling status with a broader support team

For athletes, it may be useful after:

• contact knee injury
• twisting injury
• heavy training block
• return-to-run progression
• return-to-jump progression
• high-volume field sessions

For general population clients, it may help monitor:

• post-activity swelling
• stiffness after walking
• swelling after stairs
• post-operative response
• recurring knee irritation

For Measurz users, the main value is consistent recording of swelling grade, side-to-side difference, pain, stiffness, activity context and change over time.

How to Record This in Measurz

Record:

• test name: Sweep Test
• side tested: left, right or both
• result: positive, negative, unclear or unable to test
• effusion grade if used
• visible wave or bulge: yes / no
• location of bulge
• client position
• knee position
• hand sequence used
• pain score from 0–10
• stiffness or fullness reported
• warmth if assessed
• comparison side
• activity completed before testing
• time since injury, surgery or training
• irritability level
• reason for stopping if stopped early
• related findings, such as patellar tap, ROM, girth, pain with movement or functional tests
• interpretation notes
• planned retest date

Record whether the main finding was:

• no effusion
• trace effusion
• small effusion
• moderate effusion
• large effusion
• unclear response
• unable to test safely

This improves:

• repeatability
• communication
• client education
• assessment reasoning
• team consistency
• progress monitoring
• long-term reporting

Related Tests / Internal Links

• Patellar Tap Test
• Ballottement Test
• Knee Girth Measurement
• Knee Range of Motion Tests
• Thessaly Test
• McMurray Test
• Anterior Drawer Test
• Posterior Drawer Test
• Pivot Shift Test

FAQs

What does the Sweep Test assess?

It assesses whether fluid may be present inside the knee joint.

What is a positive Sweep Test?

A positive result may include a visible wave, bulge or refill of fluid around the medial knee after sweeping fluid around the joint.

Does a positive Sweep Test diagnose a knee injury?

No. A positive test may suggest knee effusion, but it does not identify the cause of swelling.

What is the difference between the Sweep Test and Patellar Tap Test?

The Sweep Test is often used for small to moderate effusions. Patellar tap or ballottement is often more useful when a larger effusion is present.

Can the Sweep Test monitor progress?

Yes. Repeating the test with the same method can help monitor whether swelling is improving, worsening or staying the same.

Is the Sweep Test reliable?

A 2009 study of a modified stroke test grading scale reported substantial inter-rater reliability, with kappa around 0.64, but consistency depends on standardised technique and clear grading.  

Should the Sweep Test be used alone?

No. It should be interpreted with history, observation, range of motion, pain, warmth, related orthopaedic tests and functional assessment.

Key Takeaways

• The Sweep Test assesses knee joint effusion.
• It is also known as the stroke test, bulge test or effusion wave test.
• A positive finding is a visible fluid wave, bulge or refill.
• The test is useful for monitoring swelling but does not identify the cause.
• Diagnostic accuracy values for specific knee pathology are limited.
• Reliability improves with consistent position, hand sequence, pressure and grading.
• Measurz should record side, result, effusion grade, pain, stiffness, activity context, comparison side and related findings.

References

Physiopedia. (n.d.). Sweep test. https://www.physio-pedia.com/Sweep_test

Sturgill, L. P., Snyder-Mackler, L., Manal, T. J., & Axe, M. J. (2009). Interrater reliability of a clinical scale to assess knee joint effusion. Journal of Orthopaedic & Sports Physical Therapy, 39(12), 845–849. https://doi.org/10.2519/jospt.2009.3143

TeachMeSurgery. (2022). Examination of the knee joint. https://teachmesurgery.com/examinations/orthopaedic/knee-joint/