Do Culture-Negative Periprosthetic Joint Infections Have a Worse Outcome Than Culture-Positive Periprosthetic Joint Infections? A Systematic Review and Meta-Analysis

Table 4

Diagnostic parameters for CN PJI [23].

Test	Criteria	Sensitivity	Specificity
Clinical features	Sinus tract (fistula) or purulence around prosthesis	20-30%	100%
Leukocyte count in synovial fluid	>2000/ul leucocytes or >70% granulocytes (PMN)	≈90%	≈95%
Periprosthetic tissue histology	Inflammation (≥23 granulocytes per 10 high-power fields)	73%	95%
Microbiology	Microbial growth in: (i) synovial fluid or; (ii) ≥2 tissue samples or; (iii) sonication fluid (>50 CFU/ml)	45-75%; 60-80%; 80-90%	95%; 92%; 95%

Metal-on-metal bearing components can simulate pus (≪pseudopus≫), leukocyte count is usually normal (visible is metal debris)
Leukocyte count can be high without infection in the first 6 weeks after surgery, in rheumatic joint disease (including crystalopathy), periprosthetic fracture or luxation.
Leukocyte count should be determined within 24 h after aspiration by microscopy or automated counter; clotted specimens are treated with 10 μl hyaluronidase
Classification after Krenn and Morawietz: PJI corresponds to type 2 or type 3
For highly virulent organisms (e.g. S. aureus, streptococci, E. coli) or patients under antibiotics, already one positive sample confirms infection
Under antibiotics, for S. aureus and anaerobes, <50 CFU/ml can be significant