A good rule of thumb in treating injuries, such as a sprained knee, is to remember: spRAIN (ice pack - rain is cold); TRAIN - hot locomotive means heat.
I have periodic problems wth a knee that gives me problems. It usually flares up when I over-exert weight on it by lifting or moving heavier object that I should. I have a knee brace that I bought and wear it when this happend and it helps greatly.
