Patellar Tap
August 21st, 2017
Overview
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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