A positive patellar grind test represents patellar cartilage injury, commonly associated with chondromalacia patellae and osteoarthritis of the patellofemoral joint. The procedure is to hold a fist in the left hand and stand at the popliteal fossa of the patient, put the knee joint in a slightly flexed position, put the right hand on the top of the patella and press down to the femoral trochanter, while rotating the patella for patellar grinding, subpatellar friction can be heard and accompanied by painful symptoms, this is a positive patellar grinding test. Patients with a positive patellar grinding test usually present with knee pain, knee weakness, running, jumping, squatting and other movements can induce pain, and the pain is obvious when going up and down stairs or squatting up, and lessens or disappears when walking on a flat road. Treatment includes enhancing quadriceps strength, improving joint stability, and intra-articular injection of sodium vitreous acid to reduce patellofemoral joint wear. If conservative treatment is not effective, arthroscopic surgery can be performed to repair the articular cartilage and restore the flatness of the joint.