, Ligament damage, Meniscus damage or Patello-femoral disorder.
You have mentioned that you have pain on kneeling down that is in extreme flexion. This suggests that it might be due to either meniscus injury or due Patello-femoral disorder.
The location of pain says that it might be due to meniscus problem.
When did your pain begin, what were you doing at the time, and what were the initial symptoms?
Do you experience any grinding, locking, catching, or giving way of the knee?