You must be reading that wrong. For general muscle soreness NSAIDs work fine. If there is something anatomically wrong with your knee then NSAIDs serve to reduce inflammation. This reduction in inflammation may be just enough so stuff doesn't rub the wrong way. If you have tendinitis then a heavy course of NSAIDs over a couple weeks may help. I know it has helped me. The problem is unless you know exactly what is wrong you may be doing yourself more harm than good.