i do traditional ju jitsu and received my injury from running. now however i'm in rehab and am looking at a return sometime in the next few months.but this time i will start to check more closely my form and whether breakfalls (falling on your back) affects my knees. some can have quite heavy impact, but it doesn't hurt, taht's the point of breakfalling.but i am very aware of my condition and hope to practice safely.one thing though is there is no competition in this club. my jitsu club before had and kickboxing, karate, etc which i did previously did.so possibly this is one good thing as there's nothing like the thrill of competition to let you forget all about your sore knee as you bash it about. only for the adrenaline to wear off and you realise you've done yourself an injury.at the height of my gloom i was considering tai chi, but now i hope to get back to jitsu for a few more years, maybe more there's also the weapons katas of aikido (sticks) which is great fun.so what i'm saying is, there's a MA for everyone, just use your judgement and be sensible.