I was taking the garbage to the curb on Monday night, stepping carefully on the glazed-over, crusty snow. As I returned to the sidewalk, I gingerly leaped onto the concrete only to hit a patch of ice. My feet went out from under me, making me fall backwards awkwardly. As I was about halfway down, my right foot hit firm sidewalk and instinctively tried to exert force. As I was hitting the ground, I could feel something like the plucking of a deep bass string on a guitar in my knee. I was able to get up under my own power and get back in the house, with only sore sitting bones and a gimpy knee.
The next morning, my knee was a bit stiff, but no real serious pain. I was not even limping. Most of the stiffness disappeared with the six-block walk from the Metro station to my job. I checked in with the office doctor, and he could not find any damage, aside from some pain when pulled in a peculiar way. It was a strained muscle or ligament behind the knee, probably the biceps femoris (one of the hamstring muscles). He did not prescribe any treatment, other than care about how much pressure I put on the knee. I was relieved.
Curiously, the damaged tissue is the same one, I think, that gets injured when forcing the leg into lotus position or Padmasana because of the pressure of twisting the leg at the knee to lift the foot on top of the other thigh. Today, I did a full session of yoga without any difficulty, but I did not try lotus (nor do I ever because I’ll need a couple of years to work into it). I could even do something like pigeon pose without causing discomfort.