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.
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.
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
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.
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.
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
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
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.
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
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
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 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
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
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.
Keep the knee relaxed.
Monitor for:
quadriceps contraction
muscle guarding
skin tension
discomfort
movement of the limb
inconsistent hand pressure
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.
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.”
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.
A negative finding involves:
no visible wave
no medial bulge
no refill
no clear side-to-side swelling difference
no visible response after sweeping
Stop if:
pain increases
the knee is too tender
skin irritation is present
the client asks to stop
red flags suggest medical review
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
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.
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.
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 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
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.
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
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
It assesses whether fluid may be present inside the knee joint.
A positive result may include a visible wave, bulge or refill of fluid around the medial knee after sweeping fluid around the joint.
No. A positive test may suggest knee effusion, but it does not identify the cause of swelling.
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.
Yes. Repeating the test with the same method can help monitor whether swelling is improving, worsening or staying the same.
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.
No. It should be interpreted with history, observation, range of motion, pain, warmth, related orthopaedic tests and functional assessment.
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.
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/
