Hello.
Yes, knee and joint pain can inhibit your enjoyment of sex. I suggest you experiment with different positions. I recommend the scissors position, in which the two of you lie side by side, facing each other, with your legs wrapped around your partner. This doesn't strain your knees. Also try sitting in your partner's lap.
There's an excellent book with more ideas about how to minimize pain during sex:
"The Ultimate Guide to Sex and Disability: For All of Us Who Live with Disabilities, Chronic Pain, and Illness," by Miriam Kaufman
Best of luck. Dr. J
A few suggestions: Your partner can be on top. You can both lay in the spoon position (facing the same wall), using a stool or something a bit higher then the bed, you can stand (if you are the male) and do it while she is on her back or in doggy style (on her hands and knees)