Sunday, November 13, 2016

What if aseptic loosening is not aseptic?

Emperor's new clothes: Is particle disease really infected particle disease?

These authors point out that loosening remains the most significant (70%) long-term complication of total hip replacement and that inflammatory response to wear particles is thought to be its main trigger. The clinical presentation includes pain and osteolysis. The diagnosis of 'aseptic' is based on the absence of evidence of infection. But as the authors state, 'the absence of evidence is not evidence of absence'.

Recently, there have been increasing numbers of positive bacterial isolates and other evidence of bacterial presence reported among patients with clinically absent infection.  Such evidence can be missed for many reasons, including failure to submit multiple specimens for culture, failure to submit tissue specimens of sufficient size, failure to sonicate or vortex retrieved implants, reliance on cultures of joint fluid (that will not reveal sessile bacteria in a biofilm), failure to observe cultures for sufficiently long, failure to culture specimens on aerobic and anaerobic media, bacterial fastidiousness or dormancy, presence of prophylactic antibiotics, attribution of positive culture results to 'contamination',  use of complex and arbitrary definitions for 'infection', failure to use non-culture methods for bacterial identification and others.

These authors also point out that bacterial presence may alter the response to micro particles of cement, polyethylene, and bone as well as the ability of bone to maintain itself and integrate with a prosthesis.

Comment: In the shoulder world, we've learned that while some periprosthetic infections are obvious, it is common for revision surgeries for shoulders presenting as pain, stiffness or loosening to yield multiple positive cultures. 

We suggest that a meaningful way to present the culture results from a revision surgery is to indicate the number and sources of the specimens submitted for culture, the culture protocol, and the number of cultures that are positive for each organism. This approach frees us from trying to decide if the joint is 'aseptic' or not, or if it meets someones definition of 'infection'. With these data we may be able to resolve the role that positive cultures play in the presentation and management of failed arthroplasties.

We all remember the time when ulcers were 'caused by acid' before the importance of H. Pylori was recognized.


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