Pathways by which Debris from Implants Interact with the Body's Immune System are Identified
New York, NY (October 25, 2011) - Joint replacement is one of the most common surgical procedures performed in the United States, with over 250,000 hip and 500,000 knee replacements implanted each year. However, some patients suffer premature failure of the procedure due to the body's reaction to the tiny particles that the devices shed as they wear. Now researchers at Montefiore Medical Center and Albert Einstein College of Medicine of Yeshiva University have identified a number of cellular pathways that are involved in this response to the debris resulting from everyday use and wear which often result in pain, damage and inflammation. These findings are summarized in a review paper published in the October 2011 print edition of Nature Reviews: Rheumatology.
"Debris is caused by wearing-out of implants through movement and bearing weight. Even when you walk, there is friction," said co-author Laura Santambrogio, MD, PhD, Associate Professor of Pathology, Immunology and Microbiology at Einstein. "The immune system is instructed to recognize debris, so the body recognizes these particles and tries to break them down. Since their size and chemical composition make the particles very resistant to degradation they linger in the body and inside immune cells which results in inflammation."
"Younger and younger patients are receiving knee and hip replacements, so they place greater demand on the implants and need them to last a longer period of time," said co-author Neil J. Cobelli, MD, Chairman of the Department of Orthopaedic Surgery at Montefiore Medical Center and Professor of Clinical Surgery at Einstein. "The biological response to the particles of wear debris is the single biggest reason why joint replacements fail."
Polyethylene is one of the earliest and still the most commonly used bearing surface material for joint replacements, but many patients experience an immunological reaction to particles of this material. As a result, metal-on-metal bearings (cobalt chromium alloy) were introduced as an alternative for hip replacements. But the body's immune reaction to all-metal hips implants is proving to be very problematic and as complaints regarding all-metal hips have increased, their use has plummeted to about five percent of the market. In fact, over the past year, the FDA has received hundreds of complaints related to several widely used devices known as metal-on-metal hips.
"We have discovered the smaller the particulate debris from the implant, the greater the effect is on the immune system, and thus there is an increase in tissue damage," said Dr. Santambrogio.
"Knowing why this reaction happens on a cellular level is important in trying to prevent these particles from causing such a debilitating biological response and for generating less reactive biomaterials that are more wear resistant," said Dr Cobelli.