Thursday, November 10, 2011

How to decide if a joint is infected - AAOS proposed guideline

An American Academy of Orthopaedic Surgeons work group has proposed a new definition for an infected joint replacement. The authors state: "Both the orthopaedic community and the surveillance authorities such as the Centers for Disease Control and Prevention (CDC) continue to be frustrated by the lack of a standard definition for periprosthetic joint infection (PJI). Interpretation of available literature is becoming increasingly difficult because centers and investigators use different—and at times conflicting—definitions for PJI."

The workgroup suggested that a DEFINITE diagnosis of prosthetic joint infection can be made if
the following conditions are met:

A sinus tract communicating with the prosthesis; or
A pathogen is isolated by culture from two separate tissue or fluid samples obtained from the affected prosthetic joint; or
Four of the following six criteria exist:
-Elevated serum erythrocyte sedimentation rate (ESR) or serum C-reactive protein (CRP) concentration
-Elevated synovial white blood cell (WBC) count
-Elevated synovial neutrophil percentage (PMN%)
-Presence of purulence in the affected joint
-Isolation of a microorganism in one culture of periprosthetic tissue or fluid
-Greater than five neutrophils per high-power field in five high-power fields observed from histologic analysis of periprosthetic tissue at 400 times magnification.

However, the authors note that PJI may be present even if fewer than four of these criteria are met.

The particular challenge is that, as pointed out in a previous post, these criteria are often not met when a shoulder arthroplasty is infected with the most common organisms seen in the shoulder: P Acnes and Coag Negative Staph.

These infections are subtle and need to be made by careful clinical observation and special culturing methods.


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