54
· DOS Abstracts
Prosthetic Joint Infection (PJI): Bacterial Identification
with Heat Flow Detection in Sonication Fluid of Removed
Total hip or knee Arthroplasty (THA/TKA)
Christen Ravn, Michael Kemp, Per Kjærsgaard-Andersen, Søren Overgaard
Orthopaedic Research Unit, University of Southern Denmark; Department of
Clinical Microbiology, Odense University Hospital; Department of Orthopaedic
Surgery, Vejle Hospital; Department of Orthopaedic Surgery and Traumatology,
Odense University Hospital
Background:
In PJI a delay of 5-10 days after surgery is frequent before bac-
terial diagnosis by conventional culture methods. Introduction of sonication for
biofilm dislodgement of removed implants have increased the sensitivity of PJI-
diagnostics as compared to culture of biopsies (Trampuz et al. NEJM, 2007).
Microcalorimetry can demonstrate microbial growth in small fluid samples as
measured by heat flow (µW), and may even give a more rapid diagnosis than
simple culture.
Purpose / Aim of Study:
To compare microcalorimetry with culture of sonica-
tion fluid for bacterial detection, and to evaluate the time to detection (TTD) of
bacterial presence by microcalorimetry.
Materials and Methods:
We analyzed prosthetic components removed during
joint revision for deep infection (Dinf) or aseptic loosening (Asl) of THA and TKA.
The prostheses were individually sonicated before aerobic and anaerobic culture,
and checked for positive growth (>20 colonies/ml) twice daily. Furthermore
sonication fluid (SF) was analyzed with microcalorimetry (TA Instruments) for
48 hours. TTD (hours) was defined as time to reach a detection limit of 10
µW.
Findings / Results:
In 111 revisions of THA (70) and TKA (41) indications
were resp. Dinf (49) and Asl (62). Sonication fluid was found culture positive in
50 cases, whereas microcalorimetry was positive in only 35 (sensitivity 0.70 /
specificity 0.93) with a mean TTD of 9.4 hours (range 1.5-29.4). Bacterial find-
ings of microcalorimetry appears as species (no./mean TTD): S.aureus (9/6.4),
E.faecalis (7/8.2), streptococcus sp. (4/12.3), E.coli (1/12.7), and coagulase
neg. staph. (13/14.3). Bacteria not found incl. CNS (3), P.acnes (2) and strep-
tococc sp. (2).
Conclusions:
Microcalorimetry of sonication fluid demonstrated good specific-
ity, but rather low sensitivity. A bacterial diagnosis was rapidly found (mean 9.4
hr) by heat flow detection.
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