I m a 24 year old female. I am a long distance runner, but I have taken the past 4 months off due to pain in my knee. I do have an appointment this week, but I thought I d get a head start and wanted to know specific questions I should ask my doctor when I see him. 3 months ago, I was sitting on a stool. I hopped down gently and I experienced the worse pain I ve ever felt in my knee. It sort of locked up and I was unable to bend it without excruciating pain. That lasted a day or so, and the pain got better. However, starting that day, and every day since, there has been a strange feeling in my knee. It feels unstable--especially when going down the stairs. I also cannot squat comfortably. There is a hard floating object on the outside of my knee. At first, I thought it was a tendon or muscle because I could pop it back (I likened it to the top of a soda fountain drink--where you can push in cola, diet, other, etc. ). When I extended my knee, it would pop back out. I should be clear that it is not my patella that is moving. It doesn t cause any pain day-to-day, but I cannot comfortably run because it feels unstable.