With Baby Boomers entering their 60s the number of knee replacement surgeries is on the rise. While most of these operations are successful, not all are.
Orthopedic surgeons say most knee replacements will function well for years, but patients should be aware of the signs of failure -- including increased pain or decreased function -- that may require a corrective procedure known as revision total knee replacement, if necessary.
"A failed knee implant is usually caused by wear and tear with subsequent loosening of the implant. Other causes are infection, instability, fracture, or stiffness," said Dr. Amar Ranawat, a hip and knee specialist in the Adult Reconstruction and Joint Replacement Division of Hospital for Special Surgery in New York City.
The most common symptoms of a failed knee implant are pain, instability, swelling and stiffness across the entire knee (generalized) or in a small section (localized).
Reasons for failure
Although knee replacements normally perform well for at least 15-20 years in more than 95 percent of patients, Ranawat says there are five primary reasons why a knee implant fails:
• Wear and loosening: Friction caused by joint surfaces rubbing against each other wears away the surface of the implant causing bone loss and loosening of the implants.
• Infection: Large metal and plastic implants can serve as a surface onto which bacteria can latch.
• Fracture: Fractures around the knee implant that disrupt its stability may require revision surgery.
• Instability: A sensation of the knee "giving away" may mean that the soft-tissue surrounding the knee is too weak to support standing and walking. Improperly placed implants may also cause instability.
• Stiffness: Loss of range of motion, which causes pain and a functional deficit.
The fix
Revision total knee replacement is a complex procedure that requires extensive pre-operative planning, specialized implants and tools, prolonged operating times and mastery of difficult surgical techniques. It usually takes longer to perform than the original knee replacement.
Ranawat says more than 80 percent of patients who undergo revision knee surgery can expect to have good to excellent results. However, he cautions that complete function is not restored for all patients and "up to 20 percent of patients may still experience pain following surgery for months or even years."
