Why does it feel like my knee often pops out of place?

What's popping: Sometimes the kneecap feels like it moves in and out of place. Or, perhaps you feel something internal in the knee that is not smooth. Could be something like a meniscus or cartilage injury. Generally, those would be associated with pain and swelling. Different things in the knee can cause the sensation of popping, and if associated with pain or instability, it is worth evaluation by an ortho.