My knee is giving out?

my knee has been giving out on me on rare occasions, and instead of bending the way my knee is supposed too, it bends sideways, and it's almost like it pops out of joint. it's extremely painful when it happens, but once it happens it hurts for 10 seconds tops and then slowly the pain dimishes. If I get up, I limp for a while, and then my knee goes back to normal.
it started doing this when a kid stomped on the inside of my knee a few years ago. it's happened a total of 5 times. and the more it happens, the more often it does it.
somebody help. I'm only 18, and i hope to god i don't have permanent knee problems.
Answer:
You should probably go see a doctor and see what they say.

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It sounds like your ACL (anterior cruciate ligament) was severed. You're going to need to go to an orthopedic surgeon to get x-rays or an MRI. If that is your problem, they can perform surgery to reattach a piece of ligament taken from another part of your body (probably hamstring), and after 6 months of physical therapy you should be almost as good as new. Even if it is not severed, it sounds like you will need some physical therapy for a while.You can function without your ACL, with just physical therapy, but you'll need a strong custom knee brace in order to do sports like skiing. If you don't have the surgery, it can go out again at any time.

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