BallottementWith the knee extended, apply downward pressure on the suprapatellar pouch with the web or the thumb and forefinger of one hand, and then push the patella sharply downward against the femur with a finger of your other hand. If in a effusion is present a tapping or clicking will be sensed when the patella is pushed against the femur. Release the pressure against the patella but keep your finger lightly touching it. If an effusion is present the patella will float out as it for a fluid wave were pushing it.