Sweep Test

The Sweep Test (also known as Knee Hydrops Test, Knee Effusion Test, Effusion Wave Test, Bulge Test, Patella Sweep Test, or Brush Test) is a clinical examination used to evaluate joint effusion in the knee. Effusion is usually caused by injury to intra-articular structures such as the meniscus, ligaments, or synovial tissue, and may result from trauma, overuse, or inflammatory conditions.

Joint effusion may be present even without visible swelling, and the Sweep Test makes it possible to detect small amounts of intra-articular fluid during clinical examination. The test is often performed alongside other assessments, such as the Ballottement Test and Fluctuation Test, to confirm or exclude findings.

Purpose

The Sweep Test aims to:

• Detect minimal joint effusion in the knee

• Differentiate between normal synovial fluid levels and pathological effusion

• Assess joint status in patients with knee injury or suspected inflammatory processes

Clinically Relevant Anatomy

The knee joint capsule surrounds the femur, tibia, and patella. Intra-articular fluid is normally produced to reduce friction and nourish cartilage. When injured or irritated, fluid production may increase, leading to effusion. Fluid often accumulates in the suprapatellar bursa and around the joint line, which allows the examiner to displace it during testing.

Execution

• Patient position: The patient lies supine with the knee fully extended and relaxed

• Medial sweep:

  • The examiner places their hand medially, past the tibiofemoral joint line

  • Using flat fingers, the examiner performs 2–3 upward strokes toward the suprapatellar bursa to move fluid to the superior capsule

• Lateral sweep:

  • The examiner then performs a downward stroke laterally, from the suprapatellar bursa toward the lateral joint line

  • Any displaced fluid will shift to the medial joint line beneath the patella

• Observation:

  • Look for a visible fluid wave or bulge on the medial side, below the patella

Interpretation

• Positive test: A fluid wave or visible bulge appears medially after the lateral downward stroke, indicating intra-articular effusion

• Negative test: No fluid wave or bulge is observed

Classification of Findings

Results can be graded on a 5-point scale:

• 0: No effusion

• Trace: Small bulge medially

• 1+: Larger bulge medially

• 2+: Fluid returns to the medial side without performing a downward stroke

• 3+: Effusion so large that fluid cannot be displaced

Evidence

• Sweep Test demonstrates high inter-tester reliability with a Cohen’s kappa value of 0.75 (good agreement)

• Perfect agreement in 73% of cases

• No assessments differed by more than 2 grades between examiners

• Ballottement Test and Fluctuation Test have shown lower reliability (0.21 and 0.37, respectively)

• Validity is clinically well-accepted, but detailed sensitivity and specificity data are lacking

Clinical Relevance

• Useful for detecting even small amounts of fluid in the knee, which may not be visible on inspection

• Applicable in suspected intra-articular injury (e.g., meniscal injury, synovitis) and in postoperative evaluation

• Can be combined with Ballottement and Fluctuation Tests to strengthen diagnostic accuracy

Limitations

• Difficult to interpret in cases of large effusion (3+) as the fluid cannot be easily displaced

• Interpretation may be complicated by significant soft tissue edema or scar tissue

• Should always be evaluated in the clinical context alongside history and other findings

Summary

The Sweep Test is a simple, reliable, and widely used clinical test to assess knee joint effusion. It is particularly suited for identifying small amounts of intra-articular fluid that are not always visible during inspection. With high inter-tester reliability, it is valuable in both acute and follow-up settings for knee assessment.

Sources:

1. David J. Mathison, MD*Þ and Stephen J. Teach, MD, MPH*Þ Pediatric Emergency Care Issue: Volume 25(11), November 2009, pp 773-786

2. Fritz JM, Delitto A, Erhard RE, Roman M. An examination of the selective tissue tension scheme, with evidence for the concept of a capsular pattern of the knee. Phys Ther. 1998;78:1046-1056; discussion 1057-1061. http://ptjournal.apta.org/content/78/10/1046.full.pdf+html

3. Interrater Reliability of a Clinical Scale to Assess Knee Joint Effusion Patterson Sturgill et al.; Journal of Orthopaedic Sports Physical Therapy 39 (2009) 845-849