Ginger Thing's spot on about the stirrups. I smashed up my knee a couple of years back (came off my bike, nothing as exciting as what you do though - I was on my way to work!). I was really worried that I might not be able to ride afterwards, the docs were pretty downbeat about it all. Fortunately it's recovered very well but it still gets sore. Bendy stirrups are fab, there are cheapo ones now - mine cost £25 - and if you want to avoid faffing, get some leathers too & it's easy to whip off the RS kit & whack yours on before you ride. Added bonuses are not having to spend ages getting stirrups to the correct length & knowing your leathers are in good nick & won't break at an inconvenient moment. Also, if your knees are starting to ache, pop your feet out the irons & give your legs a good wave around to loosen them up. I find taking glucosamine & cod liver oil is really good to keep your knee joints 'sound' too. Good luck, pesky knees!