A "tap on the knee," in a medical context, refers to a specific maneuver performed during a physical examination of the knee to check for fluid accumulation (effusion).
Knee Tap Examination Explained
The knee tap is a test used to detect knee effusion, where excess fluid builds up in the knee joint. Here's how it works:
- The Procedure: While applying pressure with one hand around the knee, the examiner uses the fingers of the other hand to press down sharply on the kneecap (patella).
- Positive Result: According to the reference, "If a knee effusion is present, the kneecap will move down and "tap" the bone beneath." This sensation of the kneecap tapping against the bone indicates the presence of fluid separating the patella from the bone. This happens because the fluid displaces the kneecap, allowing it to move more freely.
- Negative Result: If no effusion is present, the kneecap will not move significantly or "tap" the bone.
Why is the Knee Tap Test Important?
Detecting a knee effusion can help determine the underlying cause of knee pain, swelling, or stiffness. Conditions that can cause knee effusion include:
- Osteoarthritis
- Rheumatoid arthritis
- Injuries (ligament tears, meniscus tears, fractures)
- Infections
