I'm 72, no physical problems, physically active all my life, Running, Dancing & Surfing.  2 Years ago I join a gym to work on my core since I can't run as much as I did when I was younger. I've run 60+ full marathons and All 35 of the LA Marathons and and hundreds  10k’s, 5k’s &  ½ Marathons. I'd like to continue. Before running LAM #35 I had pain in my right knee. After running the LAM#35 the pain got really  bad I could not walk on my right knee. My right knee swelled, then my leg and then my foot. I was rowing, riding my bike, and running, I quite all for 6 weeks. I kept my leg elevated and iced daily. Swelling went down & pained reduced to the point I could walk down a flight of stairs without holding on to the rail. The pain has reduced by 70%.  I cannot turn or disassociate on my right knee without lots of pain. Lots of popping in the knee, I can't negative flex the knee. I have no strength in my knees and squats are very difficult. Good news is  I can walk normally.  Kaiser x-ray results below. Dr.Woodward at Woodland Hills. The pain is a lot worse than the x-ray showed.
I’m considering Stem Cell injections.
What is the difference between Stem Cell & PRP?

STEOARTHRITIS OF RIGHT KNEE
Note: mild. Patellofemoral pain is dominant. Improving with mobic
Continue mobic
Icing as needed 
Brace with activity 
Good shoes/no bare feet replace every 400 miles
Recommend core and hip home exercise program 
No distance running until near pain-free and able to do squatting without pain
Can do steroid injection if not responding by 6-8 weeks. 
Consider turmeric with black pepper 
voltaren gel twice a day as needed