I had a similar tear after total knee replacement. Mine most likely happened during rehab before leaving the hospital. Mine tore on the foot side at the patella. Because of the swelling and pain post replacement, I didnt find out for several weeks. I had both knees replaced the same time. It has been 9.5 months and i've shed the braces and use a cane just in case. It will take some time, listen to the doc and phy therapist but take it slow. I have -10 to +110 flex and am riding a bicycle again. About 15 degrees from straight leg is still very weak, hence the cane but I think it will recover.You got to have faith because the thought of limited mobility is not an option. I'm 56 and push 200lbs. Get to a gym and good luck !