Pathologic degradation of collagen found in loosened hip replacement implants


NEW YORK (Reuters Health), Oct 24 - Successfully placed artificial hip joint implants frequently become loose many years after the original surgery. Now, researchers in Finland and the Netherlands have shown that this degradation is due, at least in part, to activated enzymes that target the fibrous connective tissue capsule that directly surrounds the joint.

Surgeons have observed that, at the time of revision surgery, these joints are surrounded by a fibrous connective tissue capsule, which itself is covered by a synovial membrane-like lining. What remains unknown, the investigators note in the September issue of Arthritis and Rheumatism, "is if the locally synthesized proproteinase enzyme proteins are activated and are able to overcome their endogenous inhibitors (i.e., if they indeed degrade interface membrane collagen matrix)."

To investigate, Dr. Yrjo Konttinen, from the Helsinki University Central Hospital, and colleagues analyzed synovial membrane-like interface tissue samples from nine patients undergoing revision or total hip replacement due to loosening that had occurred 10 to 22 years after the initial placement. These tissues were compared with control tissue, removed from nine patients requiring surgery for a broken hip.

Chemical analysis showed that the degree of collagen degradation differed significantly between loosened joints and control joints (mean 20% versus 12%, p = 0.007), according to the researchers. Moreover, the pathologic tissue had higher extracellular levels of three enzymes -- matrix metalloproteinase 1 (MMP-1), MMP-13, and cathepsin K.

Correlation analysis showed that in the loosened implant, but not the control tissue, the levels of these three enzymes were also significantly associated with the degree of extracellular collagen breakdown.

Sorting out the role of each enzyme is the next step, Dr. Konttinen's team indicates.

Arthritis Rheum 2006;9:2928-2933.

Last Updated: 2006-10-23 13:44:05 -0400 (Reuters Health)

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