Three years ago, I had my left knee joint replaced. For the last 18 months, I’ve had uncomfortable swelling in that joint. The doctor thinks it might be a failed kneecap. A second operation is advised. What will be done?

There are several possible reasons why the kneecap portion of your total knee replacement (TKR) has gone bad. The lining behind it may have cracked or worn away. The pegs holding it in place may be broken.

The doctor will need to look inside the joint to see what’s going on. Loose fragments of bone, cartilage, or the implant will be removed. Sometimes, the lining of the joint, called the synovium must be cut or removed.

The doctor will look at the implant and the joint surface for any defects or problems. Knee motion and implant alignment will be checked. The kneecap should move up and down along a track as the knee bends and straightens. A decision about what to do will be made on the basis of these findings. The replacement kneecap may be fixed or replaced again.