ACL injuries are common in people who play sports that involve a lot of jumping, weaving, or sudden stops and starts.

But as we get older, even simple movements ...

like stepping off a curb ... can cause an ACL tear.

The anterior cruciate ligament ... or ACL ... is a strong piece of fiber that connects your thighbone to your shinbone.

Its job is to help keep your knee stable.

If you tear your ACL, your knee may feel unstable or give out on you ...

and you may need surgery to fix it.

ACL surgery can usually be done through a few small cuts, or incisions, around the knee.

The doctor puts a thin tool called an arthroscope into one of the incisions.

The scope has a camera that sends pictures to a monitor.

This lets the doctor see inside the knee without making a large incision.

A torn ACL can't be sewn back together.

Instead, it has to be replaced with another piece of tissue called a graft.

The graft may come from your body or from another source.

To place the graft, the doctor uses a small drill to make holes in the leg bones where they come together in the knee.

The graft is pulled through these holes and fastened in place.

Then the incisions are closed with stitches or tape and covered with a bandage.

The whole surgery takes about an hour.

Your leg will be moved a lot during surgery ...

so afterwards, your thigh and calf ... as well as your knee ... will be sore.

You'll get medicine to help ease the pain.

You'll probably be able to go home after a couple of hours in the recovery room.

You'll need to use crutches for a week or two ...

but you may be able to put weight on your leg if you have a brace on.

Rehab will start in the recovery room ... right after surgery.

It's hard work ... and it may take several months ...

but it's the key to helping your knee become strong, flexible, and stable again.