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Patellar tap


The subject lies supine with the knee extended or flexed to discomfort. The examiner stands level with the knee. The web of one hand is on the suprapatellar pouch. The thumb and middle finger of the other hand press at the medial and lateral recessi, just beyond the patellar edges.


Manual pressure empties the recessi and moves the fluid between patella and femur. The index finger of the other hand pushes the patella downwards. If fluid is present, one can feel the patella move. When it strikes the femur, a palpable tap is felt followed by an immediate upwards movement.

This is the sensation of an ice cube pushed downwards in a glass of water: although the patella moves downwards, the pressure of the fluid immediately shifts the bone upwards against the palpating finger. Remark: when large mounts of fluid are present,the tap of the patella hitting the femurcannot be felt.

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