Common causes are: osteoarthritis of the knee (also called gonarthrosis), damage to ligaments (anterior cruciate ligament, posterior cruciate ligament, medial collateral ligament or MCL, lateral collateral ligament or LCL, medial meniscus, lateral meniscus), tendons (crow's foot tendonitis, patellar tendonitis, iliotibial band syndrome, dislocation of the kneecap, and radiating pain from a lumbar problem (L4-L5).

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