In knee effusion assessment, which test confirms a palpable joint effusion?

• A. Lachman test
• B. Ballottement test
• C. McMurray test
• D. Apley compression test

Answer: (B)

Ballottement of the patella is used to confirm a palpable knee effusion. When fluid accumulates in the joint, pressing on the suprapatellar pouch moves fluid into that space, and tapping or pushing on the patella causes it to rebound against the femur, producing a distinct floating sensation or "ball" felt by the examiner. This visible or palpable rebound indicates intra-articular fluid.

The other tests focus on ligaments or menisci and do not specifically detect a joint effusion: one assesses ACL laxity, another checks for a meniscal tear with rotation and pressure, and the last also stresses the menisci with compression. So ballottement is the test that best confirms a palpable effusion.