Wait, you just getting back from KNEE SURGERY and now you want to jump back into training your legs 3x/week??
Like, wtf dude?
What was the nature of the knee injury? If it's like 98% of them the LAST thing you should be focusing on is destroying the quadriceps, but developing your hamstrings, glutes, and hips to enforce proper tracking of the knee. If you haven't already I'd invest in Robertson's "Bullet Proof Knees."
Sounds like you're going to grind yourself right into another knee injury.