The most common reason for failure and subsequent revision surgery is loosening of the artificial implant from bone. The cause of this loosening is complicated, but this is a known problem with artificial joints and loosening is not usually a failure of the surgeon doing it. Wearing of the plastic bearing may also result in the need for a new bearing. Newer plastics for the bearing surface have improved the longevity of knee replacements and represent an exciting improvement in these implants used during your knee replacement surgery.
Recent studies are showing that the most common cause for failure of joint replacement going into the next decade will be infection of the implant. The complexity of care, time involved and all around costs to revise these failed knees will make caring for this problem extremely expensive.