Major Effusion Test

The Effusion Test (Major) (also known as the Patellar Tap Test, Ballottement Test, or Major Effusion Test) is a clinical assessment used to detect significant intra-articular fluid accumulation within the knee joint—commonly called a “knee effusion”. Large effusions can result from acute injury (like ligament/meniscus tears), inflammation, or degenerative joint disease.

How the Test is Performed

• Client position: Supine (lying flat), knee extended and relaxed.

• The examiner “milks” or pushes fluid from the suprapatellar pouch (just above the kneecap) downward toward the knee by sliding the hand proximally to distally.

• Next, with one hand maintaining pressure, the examiner uses the other hand to push down on the patella (kneecap).

  • In the presence of a large effusion, the patella will feel as if it “floats” on the joint fluid, and with mild downward pressure, the examiner will sense a “tap” or “bounce” as the patella contacts the underlying femur.

  • This is referred to as a ballottable patella, and is strongly indicative of a major knee effusion.

• Compare with the unaffected knee for increased accuracy.

• Other associated tests for smaller effusions include the “Bulge sign” (for minor) and the “Balloon test” (for moderate effusions).

Clinical Significance

• A positive Major Effusion Test indicates a significant amount of fluid within the knee joint capsule, frequently seen after acute trauma (ACL, meniscus), inflammatory arthritis, or infection.

• Large effusions may restrict motion, cause pain, impair muscle function, and may signal serious joint pathology requiring further investigation or drainage.

• Distinguishes intracapsular (joint) swelling from extracapsular causes (bursa, fat pad, etc.).

Assessment

• Use this test in clients with acute knee swelling, pain, loss of motion, history of trauma, or suspicion of joint inflammation.

• Document the size, timing, and nature of the swelling, and whether the patella is ballotable (floats/bounces); compare with the unaffected knee.

• Always differentiate true effusion from prepatellar bursitis or fat pad swelling, which are extra-articular.

Treatment

• If positive:

  • Avoid deep tissue, aggressive massage, or joint mobilization around the swollen knee until cleared by a healthcare provider.

  • Focus on gentle edema management (light lymphatic drainage, elevation, pain relief), and supporting overall comfort.

  • Educate about rest, elevation, ice, and prompt medical referral if traumatic, painful, or unresolving—large effusions may need aspiration or imaging.

  • Avoid heat or vigorous compressive techniques until acute swelling resolves.

Safety and Referral

• Refer for urgent medical assessment if signs of infection, severe pain, inability to bear weight, or suspicion of internal joint injury are present.

• Collaborate with physiotherapy/orthopedics for joint protection and gradual rehab if effusion recurs or persists.