Which sign indicates a moderate-to-large knee effusion on examination?

• A. McMurray test
• B. Lachman test
• C. Ballottement test is positive
• D. Valgus stress test

Answer: (C)

Ballottement signals a knee effusion, especially when it’s moderate to large. In a knee with excess joint fluid, the patella can be pushed against the femur and then rebound or “ballot” back into place, producing a palpable tap or clunk as the fluid is displaced. This floating sensation is the hallmark of a larger effusion.

The other maneuvers target structures other than the presence of fluid: McMurray tests for meniscal tears, Lachman checks ACL integrity, and the valgus stress test assesses the medial collateral ligament. These tests do not assess intra-articular fluid volume, so they won’t indicate a sizeable effusion.