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Patellar Tap

August 21st, 2017


The patellar tap test assesses for an effusion of the knee joint; in a patient with a significant effusion there will be fluid behind the patella, and tapping the knee will result in a satisfying clunk as the patella makes contact with the femur posteriorly.
  • How to Perform

  • Using 2-3 fingers, sharply tap onto the patient's patella.
  • Abnormal If

  • A palpable 'clunk' occurs, when the patella makes contact with the trochlea.
  • Causes of Knee Effusion

  • Trauma - ligament tear, menisceal tear, fracture, patellar dislocation
  • Arthritis - osteoarthritis, psoriatic arthritis, reactive arthritis, IBD-related arthritis, gout, pseudogout
  • Infection - septic arthritis, tuberculosis, Lyme disease, syphilis
  • Blood - haemarthrosis
  • Malignancy - osteosarcoma
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