Some patients who undergo knee arthroplasty later experience a break or fracture in their femur.The patella, or kneecap, helps protect the femur and also helps the joint work properly. Because the kneecap is so important, if there are any problems with it, this can affect the way the knee functions and it can cause pain and discomfort. Doctors have found that fractures around the knee replacement, periprosthetic patellar fractures, which include fractures of the femur, may be the most common type of fracture that result in knee replacement complications.
The authors of this article review fractures after knee replacements have been performed, the classification systems used to identify the fractures, and the treatment decisions made by the doctors. They found there was no universal classification that could help doctors categorize the fractures, the type of treatment, and probable outcomes.
Statistics show that periprosthetic fractures occurred in 0.11 percent to 21.4 percent of patients who underwent a knee replacement. Statistics from the Mayo Clinic Joint registry list a rate of 0.68 percent of fractures in 12,000 first time knee replacements that were done over a 13-year period.
It was noted that these fractures happened nine times more often after surgery than during surgery, and more frequently in revision surgeries rather than first-time surgeries, at a rate of 1.8 percent (revision) compared with 0.7 percent (primary).
People who develop a periprosthetic fracture are not always aware of it because such fractures do not always cause pain, although patients who do have pain complain that it is located at the front of the knee, particularly when going up or down stairs. Other signs of a fracture could include weakness or instability of the knee. Many times, the fracture is only found through a routine follow-up x-ray. If the fracture is only discovered when it has been present for a while, usually no treatment is done.
The fractures can happen during or after the knee replacement. During the surgery, they can occur through the surgeon's handling of the patella, problems during surgery or with the bone itself. AFter surgery, fractures can happen from trauma, such as an accident or stress on the bone.
The researchers found that patients had an increased risk of developing a fracture if they had osteoporosis (thinning of the bones), bone cysts, weak bones, rheumatoid arthritis, and/or increased activity, or if they were men. Previous research did not find a big difference between patients who had rheumatoid arthritis or osteoarthritis, however. As well, there is disagreement as to whether gender does play a role in fractures.
Certain types of replacement design have also played a role in fractures. How the replacement is implanted can place stress on the bones, causing the fractures, particularly after a revision surgery.
How periprosthetic patellar fractures are treated depends on whether the replacement mechanism is still working and intact, how stable the kneecap compartment is, and the quality of the remaining bone. The doctors can choose to treat it conservatively, as one would normally treat a broken bone, or they choose to operate to repair it.
Several studies report varying success with conservative, nonsurgical, treatment and surgery. The authors of this study have found that if a fracture is minimally displaced, the kneecap component is still intact, and the knee is working properly, then conservative treatment, with immobilization at first, has a good outcome. In fact, often surgery did not have a good outcome. However, more involved fractures did require surgery to repair the mechanisms and bones, and to remove fragments if present.
The authors conclude that further research is needed to redefine the best surgical management for these types of fractures.
Neil P. Sheth, MD, David I. Pedowitz, MD, MD, and Jess H. Lonner, MD. Periprosthetic Patellar Fractures. In The Journal of Bone and Joint Surgery. October 2007. Vol. 89A. No. 10. Pp. 2285-2295.
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