“Dear Shay, I wanted to ask for your advice on sex positions. Now, I am personally a fan of being a receiver when it comes to sexual positions, particularly when “doggy-style” is mentioned. (What lady doesn’t, am I right?) However, my beloved has a tendency to get worn out from being such a giver. (He is also a bit older than I and he had serious surgery on his knees over five years ago.) My guy has placed me on top a few times and while I inherited extremely strong thighs, I either can’t seem to get the rhythm or I get so enthusiastic that I have almost injured my beloved’s manhood while he was inside of me. While I have only been with one man (the incredible guy I adore now and have been with for over two years), I see myself as a incredibly fast learner when it comes to sex. So, I was wondering if you had any advice when I take my mount. Thanks a bunch and keep up the great work!“
Hmm that is a bit of a tricky situation; being the top can take some practice and you definitely don’t want to end up injuring yourself or your partner. 
But, I think I might have another idea for you.
One position that is great for achieving doggy-style type penetration, but that will spare your partner’s knees is the “spooning” position; where you both lay on your sides and he penetrates you form behind. You can bend over as much or as little as you like to change the angle of penetration and he should be able to keep going for a long time since he won’t have any weight on his knees. If he can handle it, you could also try a standing version of doggy.
I hope that helps!
If your bed is high enough, a good option is to have him stand by the side of the bed and you bend over the bed. That way it’s sort of like doggy style, but he’s standing instead, which might be easier on his knees. I also really like reverse missionary. More knee friendly than doggy, but also deliciously naughty.
Hope these help!
And then there’s the “scissors”
Similar, but still
I can’t find the rhythm on top either. Husband helps me out by doing the motions from underneath me or lifting my ass up and down. Seriously, I don’t know how he can but he does.
as a guy i can say that the position in the picture works pretty well, but anything that keeps his legs straight will do the trick too.
ironically standing have be wasier than being on your knees.
the bathroom sink has many uses…
Twg – assuming his knees can handle it yeah, those are good too.
Gad – yup, a good variation, though it doesn’t get you as deep penetration
dfp – haha, can you dance? maybe you should try having sex to music ^_~
exile – depends on the sink, a friend of mine had one break under her and ended up gashing her leg open on it!
Having a bum knee myself, I have one suggestion: pillows! Get a few nice, soft, fluffy pillows (or firmer ones, whichever works better for the two of you), and put them under his knees–trust me, my (now ex-)wife and I used this trick under my bum knee, and it helped a lot! (I’ve heard that “Liberator” pads help too, but since they’re kinda expensive, you could also try borrowing the cushions off the couch or even making your own out of thick foam rubber pads or… the idea is to try extra padding to protect his knees.) If that doesn’t help, then try different positions as Shay & co. suggested already. (You could also try what I did–namely, talk to a doctor that specializes in joint disorders for some additional advice in not making his knees worse.)