Hi I Was Wearing High Heel Boots Today And Walking

hi I was wearing high heel boots today and walking down stairs. I put my left leg on a stair and all of a sudden my knee buckled. I had to limp down the stairs to get to my car. I can walk and put ice on the knee but still feel some pain on the right side of my left knee cap- could I have pulled or stained a tendon or could it be more serious? never had this happen before