Background: Molecular procedures could potentially improve diagnoses of orthopaedic implant-related
infections,
but are not yet clinically implemented. Analysis of sonication fluid shows the highest
sensitivity
for diagnosing implant infections in cases of revision surgery with implant removal. However,
there
remains controversy regarding the best method for obtaining specimens in cases of revision
surgery
with implant retention. Tissue culture is the most common diagnostic method for pathogen
identification
in such cases. Here we aimed to assess the diagnostic performance of swab PCR analysis
compared
to tissue culture from patients undergoing revision surgery of fracture fixation devices.
Methods:
We prospectively investigated 62 consecutive subjects who underwent revision surgery of
fracture
fixation devices during a two-year period. Tissue samples were collected for cultures, and swabs
from
the implant surface were obtained for 16S rRNA PCR analysis. Subjects were classified as having an
implant-related
infection if (1) they presented with a sinus tract or open wound in communication with
the
implant; or (2) purulence was encountered intraoperatively; or (3) two out of three tissue cultures
tested
positive for the presence of the same pathogen. Tissue culture and swab PCR results from the
subjects
were used to calculate the sensitivity, specificity, accuracy, positive predictive value (PPV),
negative
predictive value (NPV), and area under the ROC curve (AUC) for identifying an orthopaedic
implant-related
infection.
Results:
Orthopaedic implant-related infections were detected in 51 subjects. Tissue culture identified
infections
in 47 cases, and swab PCR in 35 cases. Among the 11 aseptic cases, tissue culture was positive
in
2 cases and swab PCR in 4 cases. Tissue culture showed a significantly higher area under the ROC curve
for
diagnosing infection (AUC = 0.89; 95% CI, 0.67–0.96) compared to swab PCR (AUC = 0.66; 95% CI,
0.46–0.80)
(p = 0.033).
Conclusions:
Compared to swab PCR, tissue culture showed better performance for diagnosing
orthopaedic
implant-related infection. Although molecular methods are expected to yield higher
diagnostic
accuracy than cultures, it appears that the method of obtaining specimens plays an important
role.
Improved methods of specimen collection are required before swab PCR can become a reliable
alternative
to tissue-consumptive methods.