Patellar tap

Patellar Tap is a clinical test used in the diagnosis of knee effusion or water on the knee. The test is performed by applying pressure to the patella (knee cap) when the knee is extended and the quadriceps are relaxed. If the patella can be tapped and a sensation of a 'tap' is felt, this is a positive sign indicating the presence of fluid in the knee joint.

Procedure

The patient is asked to lie down with the knee extended. The examiner then applies a downward pressure on the patella. If the patella can be seen to descend and then rebound, this is known as a positive patellar tap. This indicates the presence of a large effusion.

Interpretation

A positive patellar tap test indicates the presence of a large effusion in the knee joint. This can be due to various conditions such as osteoarthritis, rheumatoid arthritis, gout, infection, or trauma to the knee.

Limitations

The patellar tap test is not always reliable. It may give a false positive result if the quadriceps are not completely relaxed. It may also give a false negative result if the effusion is small.

See Also

• Knee examination
• Knee effusion
• Osteoarthritis
• Rheumatoid arthritis
• Gout
• Infection
• Trauma

References

Patellar tap Resources
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