Geezajob
Sorry don't know the limits for cholesterol, but if you're interested, the link gives some information about cholesterol inhibitors, and it doesn't make pretty reading. (There is alternative advice at the bottom of the page.) It makes sense to me, but if you are in the rather-not-know or trust-current-medical-wisdom camp (which the regulators in charge of determining medical requirements appear to belong to also), you might prefer to skip it.
Don't know anything about the knee condition but wondering if it could be related to the inhibitors you've been taking.
Be warned, I'm pretty anti-mainstream in some ways so this could be useless to you.