What Stops The Knee From Bending?

I had meniscus surgery just over three weeks ago. I can't bend my leg and when I stand up straight there is always a bend at the knee.

For the first two weeks after surgery the knee would swell up with blood that I got drain about 5 times. Man that hurts like #$%^.

Is there anything still wrong with my knee since it will not bend. The doctor said the recovery would be 2-3 weeks.