Diagnosis of infected total knee: findings of a multicenter database

Abstract

Although total knee arthroplasty (TKA) is an effective and successful procedure, the outcome is occasionally compromised by complications including periprosthetic joint infection (PJI). Accurate and early diagnosis is the first step in effectively managing patients with PJI. At the present time, diagnosis remains dependent on clinical judgment and reliance on standard clinical tests including serologic tests, analysis of aspirated joint fluid, and interpretation of intraoperative tissue and fluid test results. Although reports regarding sensitivity and specificity of all diagnostic tests in the literature are abundant, the interpretation of the available data has been hampered by the low sample size of these studies. In view of the scope of this important problem and the limitations of previous reports, a large database was assembled of all revision TKA performed at three academic referral centers in order to determine the current status of diagnosis of the infected TKA utilizing commonly available tests. Intraoperative cultures should not be used as a gold standard for PJI owing to high percentages of false-negative and false-positive cases. When combined with clinical judgment, total white cell count and percentage of neutrophils in the synovial fluid more accurately reflects PJI and when combined with hematologic exams safely excludes or confirms infection.

Level of evidence: Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Fig. 1A–B

Receiver operating curves for predicting periprosthetic infection are illustrated. An area under the curve of 1 demonstrates an ideal test with a 100% sensitivity and specificity, while an area under the curve less than 0.5 indicates that the diagnostic has poor discriminatory value. (A) The cutoff value for optimal accuracy in diagnosis of PJI was 1100 cells/μL for fluid leukocyte count. (B) The cutoff value for optimal accuracy for fluid neutrophil differential was 64%. When both tests yielded results below their cutoff values, the negative predictive value of the combination increased to 99.6%, while if both tests were greater than their cutoff values the positive predictive value improved to 100%.