Osteoarthritis, Ligament damage, Meniscus damage or Patello-femoral disorder.
Your symptom of pain at the joint line is the result of a collateral ligament or meniscus problem (or both) until proven otherwise.
When did your pain begin, what were you doing at the time, and what were the initial symptoms?
Your other symptom of feeling of grinding and grating is characteristic of osteoarthritis.
What is the quality of your pain (sharp, shooting, dull, etc.)?