The patellar grind test is used to evaluate for patellofemoral pain syndrome. The patient is supine, knee extended. Examiner places their hand along the superior pole of the patella and applies a caudal pressure. They then ask the patient to gently and gradually contract the quad muscle. In the modified version, you can ask the patient to lift their leg off the bed slightly. A positive test is patellofemoral pain and patients are often unable to complete the test.

Patellar Grind Test
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SportsMedReview: Knee Pain
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Wiki Sports Medicine: Knee Pain
https://wikism.org/Knee_Pain_Main