Okay, I looked at the site. But I have no clue what I'd need to order.
Under the "Creams/Lotions" link, any of those items would be useful for either the knee injury or arthritis--they're the same product, just different sizes/containers. Anything on the "Dit Da Jows" page would also serve the same purpose, with the difference being that those items are a little more "liquidy" in application than the cream and some have specialized functions for different phases of sports training. Unless there's something specific you have in mind mentioned there, I'd recommend one of the top two items on the Creams/Lotions link.