Understanding the Effusion tests of the Knee (Ballottement/Patellar Tap) Assessment
To detect the presence of **intra-articular swelling (effusion)**, particularly large amounts of fluid.
Watch How It's Done
How do I start?
Patient is supine with the knee relaxed and slightly extended.
What happens?
The examiner uses one hand to **milk the suprapatellar pouch** (proximal thigh) distally to force fluid toward the patella. The examiner then uses the fingers of the other hand to **firmly push the patella** down against the femur (the 'tap').
In Plain English
What Does a Positive Result Mean?
The examiner feels the patella **bounce or tap down** against the femur, indicating a significant volume of fluid pushing the patella up.
Helpful Tip:
This test is used for moderate to large effusions. The 'Bulge Sign' or 'Sweep Test' is used for smaller effusions.
Safety First
This guide is to help you understand what happens in a clinic. Do not try to diagnose yourself. If you have severe pain, swelling, or cannot put weight on your leg, please visit an urgent care center or your doctor immediately.
Other Knee Tests
Pivot Shift Test
To dynamically assess for **anterolateral rotatory instability** of the knee, which is highly indicative of a **complete ACL tear**.
Posterior Drawer Test of the Knee
To assess the integrity of the **Posterior Cruciate Ligament (PCL)**.
Posterior Sag Sign (Gravity Drawer Test)
To detect a rupture of the **Posterior Cruciate Ligament (PCL)** by observing the effect of gravity.
Slocum Test (Anterolateral Rotatory Instability)
To assess for **anterolateral rotatory instability** and the function of the **Anterolateral Ligament** (a dynamic variant of the Anterior Drawer).