Q. I'm having a knee replaced and was wondering what it will be like after the surgery.

More than nine out of 10 patients who have a total knee replacement have positive results; they experience reduced pain and improved ability to perform common activities.

Within the first year after your operation, you should increase your endurance gradually. One of the key pitfalls is trying to do too much too soon.

You'll be given physical therapy exercises for at least two months. These are designed to help you bend and extend your leg. In addition, you can walk as much as you like. Stationary bicycles are recommended for muscle tone and flexibility.

Other acceptable activities after knee surgery include dancing, golf with spikeless shoes and a cart, and bicycling on flat ground. After the wound is healed, you can swim.

Don't do anything that puts stress on the knee, including racquet sports and skiing, and don't lift anything heavier than 40 pounds.

Depending on the work or play you do, it could take six to eight weeks to get back in action.

If your left knee was replaced and you have an automatic transmission, you may be able to drive in a week. If your right knee was replaced, you shouldn't drive for six to eight weeks.

Your new knee will probably not set off metal detectors. However, you should carry a medic alert card indicating you have an artificial knee just in case.

The following is a list of modifications that can make your home easier to navigate as you recover:

• Create a complete living space on one floor.

• Remove all loose carpets and electric cords.

• Rearrange furniture so you can maneuver with a walker or crutches.

• Install a shower chair, gripping bar, and toilet-seat riser in the bathroom.

• Use assistive devices such as a long-handled shoehorn, a long-handled sponge, and a grabbing tool or reacher to avoid bending over too far.

• A stable chair with a firm cushion for your early recovery (and a height of 18 to 20 inches), a firm back, arms, and a footstool for intermittent leg elevation.

About 300,000 knee replacements are performed each year in the U.S. This surgery was first performed in 1968. There have been substantial improvements in technique and materials since then.

Some anatomy

The knee, which is the largest joint in the body, is made up of the thighbone (femur), shin bone (tibia) and the kneecap (patella). Surfaces of this joint are covered with cartilage, a smooth substance that cushions the bones and enables them to move easily. The lateral meniscus and medial meniscus are pads of cartilage that further cushion the joint, acting as shock absorbers between the bones.

In addition, surfaces of the knee are covered by a thin, smooth tissue liner called the synovial membrane. This membrane releases a special fluid that lubricates the knee, reducing friction to nearly zero in a healthy knee. Ligaments help to stabilize the knee.

A knee replacement takes about two hours. Your surgeon will remove the damaged cartilage and bone and position the new metal and plastic joint surfaces to restore the alignment and function of your knee.

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