Where to begin? first off, on whose advice are you not doing weights to rehab your knees? If you are swimming with injured knees then you need to avoid breast stroke, as the 'frog' kick it uses places great lateral strain on the knees- not good when injured. I havent met a physio yet that does not agree with steady progression through the squating movement being an excellent and safe way of rebuilding stability in the knee joint; and I have met a lot
Next. not only is your volume way too high, but you have no back work in your workout. You are on your way to physical imbalance, and all the postural, injury, and aesthetic problems that represents.
Your sudden loss of performance is overtraining, plain and simple. Take 2 weeks off training completely
-your body needs to recover badly. In this time off, you need to do a few things, the most important of all is to consult a qualified physiotherapist about your leg rehabilitation, and get a specific schedule to follow in this regard.
The next thing you need to do is re think your training. Hard work is an admirable ethic, but hard work for no reason is foolish. Train smarter, not harder.
step 1. Lets put some pulling movements in the routine
step 2. reduce the volume of pushing movements accordingly
step 3. lets look at the frequency, and make it more achievable for a human being to recover from The workout
1x12r warm up
3x6r same weight, no pyramiding
Bent over barbell row.
Spend time learning the movement before going hard at this, but when you are happy with it
1x12r warm up
in conjunction with medical plan. You may well only start with quarter squat- thats fine. Start working with you bodyweight only and concentrate on technique and building your range of movement.
Dumbell or barbell.
Lying face down on the floor, this is the exact oposite of a stomach crunch- arch the back raising your rib cage of the floor so at the top of the movement you are facing forward. Weight can be added later.
Do this on mondays and fridays ONLY. do your low impact cardio on the days inbetween as you see fit, but only 2 weights sessions per week. Providing you put all your effort into those few sets listed, you will get great benefits, and you wil also start to re-balance your bodies musculature.