Video – Patellar Ballottement Test and Bulge Sign

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Patellar Ballottement Test and Bulge Sign

The Patellar Ballottement test is used when a large knee effusion is suspected. With the patient’s knee in full extension, compress the supra-patellar pouch distally to force the fluid below the patella. Now, press the patella into the trochlear groove and then release. In the presence of a large joint effusion, the patella will seem to float and rebound.

Smaller knee effusions can be assessed by checking to see if the Bulge Sign is present. With the patient’s knee extended, begin by stroking upward along the medial side of the patella several times to force the fluid to the lateral side. Now, apply a downward stroke on the lateral side and look for the bulge to appear on the medial side.

If a knee trauma causes the rapid development of effusion (usually within 2 to 4 hours), the effusion most likely consists of blood and is called haemarthrosis. This indicates serious injuries such as a ruptured anterior cruciate ligament or intraarticular fracture.  Haemarthrosis requires immediate aspiration.

If a knee trauma causes slow development of effusion (usually within 24 to 36 hours),  the effusion most likely consists of synovial fluid and is referred to synovial effusion. This indicates conditions such as a meniscal injury or ligamentous sprain.

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