Patellar Tap Test | Ballottement Test | Knee Swelling Assessment

The Patellar Tap Test is a tool to assess for intra-articular swelling of the knee joint. Being able to assess what kind of swelling you are dealing with, gives you an idea about where the lesion could be located in the knee. With extra-articular swelling (like in prepatellar bursitis or patellar tendonitis) the test will be negative. According to Kastelein et al. (2009), this test has a sensitivity of 83% and a specificity of 49% for the presence of knee effusion. So a negative test can moderately exclude knee effusion.

To perform the patellar tap test have your patient in a supine lying position with a fully extended leg then stroke downwards just until you reach the suprapatellar pouch. Then press downwards with the other hand perform the same movement and stop just below the apex of the patella. While applying downward pressure, take one finger and press onto the patella, and see whether it’s floating.

If you can feel that the patella is floating when you’re tapping onto it this means that fluid has accumulated under it and it is an indication of swelling in the knee joint.

Another common test to assess swelling in the knee joint is the Brush/Stroke/Buldge Test.

Kastelein, M., Luijsterburg, P.A., Wagemakers, H.P., Bansraj, S.C., Berger, M.Y., Koes, B.W. and Bierma-Zeinstra, S.M., 2009. Diagnostic value of history taking and physical examination to assess effusion of the knee in traumatic knee patients in general practice. Archives of physical medicine and rehabilitation, 90(1), pp.82-86.