Background: Despite the widespread use of several diagnostic tests,
there is still no perfect test for the diagnosis of infection at the site of a
total knee arthroplasty. The purpose of this study was to evaluate the
diagnostic test characteristics of the erythrocyte sedimentation rate and
C-reactive protein level for the assessment of infection in patients
presenting for revision total knee arthroplasty.
Methods: One hundred and fifty-one knees in 145 patients presenting
for revision total knee arthroplasty were evaluated prospectively for the
presence of infection with measurement of the erythrocyte sedimentation rate
and the C-reactive protein level. The characteristics of these tests were
assessed with use of two different techniques: first,
receiver-operating-characteristic curve analysis was performed to determine
the optimal positivity criterion for the diagnostic test, and, second,
previously accepted criteria for establishing positivity of the tests were
Results: A diagnosis of infection was established for forty-five of
the 151 knees that underwent revision total knee arthroplasty. The
receiver-operating-characteristic curves indicated that the optimal positivity
criterion was 22.5 mm/hr for the erythrocyte sedimentation rate and 13.5 mg/L
for the C-reactive protein level. Both the erythrocyte sedimentation rate
(sensitivity, 0.93; specificity, 0.83; positive likelihood ratio, 5.81;
accuracy, 0.86) and the C-reactive protein level (sensitivity, 0.91;
specificity, 0.86; positive likelihood ratio, 6.89; accuracy, 0.88) have
excellent diagnostic test performance.
Conclusions: The erythrocyte sedimentation rate and the C-reactive
protein level provide excellent diagnostic test information for establishing
the presence or absence of infection prior to surgical intervention in
patients with pain at the site of a knee arthroplasty.
Level of Evidence: Diagnostic Level I. See Instructions
to Authors for a complete description of levels of evidence.