kneecap

so in this picture you can see the joint surfaces between my femur and patella (kneecap). Normally these two bones would be in contact with each other but my knee was pumped full of fluid to allow the surgery so with all that swelling the kneecap is pushed up out of the way. The red arrow shows the direction that the patella glides when you flex your knee. Again, the surfaces look nice and smooth so no damage there.