Hip and knee specialist indicates five primary reasons why knee implant fails

Jul 12 2010

While most knee replacements will function well for years, 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," says 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.

Each year, more than 300 patients elect to receive revision knee surgery at Hospital for Special Surgery, despite the fact that their original surgery was performed elsewhere.

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).

Although knee replacements normally perform well for at least 15-20 years in more than 95 percent of patients, Dr. 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.

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, says Dr. Ranawat, and is composed of the following stages:

•Pre-surgery: Preparation includes X-rays, laboratory tests, knee aspiration and in some cases additional assessments, such as bone scans, CT scans or magnetic resonance imaging (MRI).
•Surgery: The implant is removed and bone grafts may be used to fill larger areas of bone loss. In some cases, metal wedges, wires or screws may be used to strengthen the bone. Finally, specialized revision knee implants are inserted.
•Post-operative care: This is very similar to the care of the original knee replacement. Dr. Ranawat's prescription includes a combination of physical therapy, blood management and pain medication. A brace or splint may be used to protect the joint after the surgery.

Dr. Ranawat says that 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."

With the right tools at hand, revision total knee replacements can deliver the best outcomes possible. A center devoted to bone, joint, muscle and tendon conditions, like Hospital for Special Surgery, has the surgical expertise and resources necessary to deliver the best prognoses and to promise the best outcomes possible for this complex—but necessary—procedure.

SOURCE Hospital for Special Surgery