Low sensitivity of implant sonication when screening for infection in revision surgery

Figures & data

Table 1. Demographics of patients (n = 233; operations: n = 252)

	Suspected of having infection	Not suspected of having infection
Patients, n (%)	67 (28)	166 (71)
Female, n (%)/male, n (%)	37 (55)/29 (45)	115 (69)/51 (31)
Age, years, mean (SD)	64 (11)	67 (10)
Operations, n (%)	75 (28)	177 (72)
Revision, n (%)
early	33 (44)	15 (8)
late	42 (56)	162 (92)
Joint, n (%)
hips	23 (31)	54 (31)
knees	48 (64)	100 (56)
other	4 (5)	23 (13)

Table 2. Distribution of sonication fluid culture results and tissue culture results compared to whether there were clinical signs of infection in 252 revision arthroplasty surgery cases

	Clinical signs of infection
	Positive	Negative	Total
Sonicate (CFU ≥50/mL)
Positive	35	2	37
Negative	40	175	215
Total	75	177	252
Tissue cultures (≥ 2)
Positive (≥ 2)	51	35	86
Negative (< 2)	24	142	166
Total	75	177	252

CFU: colony-forming units.

Table 3. Sonication fluid cultures compared with the presence of clinical signs of infection in revision arthroplasty surgery cases

	Total cohort (n = 252)	Early revision (n = 48)	Late revision (n = 204)
Sensitivity	0.47	0.42	0.50
95% CI	0.35–0.59	0.25–0.61	0.34–0.66
Specificity	0.99	1.0	0.99
95% CI	0.96–1.00	0.78–1.0	0.9–1.00
Positive predictive value	0.95	1.0	0.91
Negative predictive value	0.81	0.44	0.88
Positive likelihood ratio	41	^a	41
Negative likelihood ratio	0.54	0.58	0.51

a error due to impossibility of calculation with reference to a specificity of 1.00.

Table 4. Periprosthetic tissue cultures compared with the presence of clinical signs of infection in revision arthroplasty surgery cases

	Total cohort (n = 252)	Early revision (n = 48)	Late revision (n = 204)
Sensitivity	0.68	0.73	0.64
95% CI	0.56–0.78	0.54–0.87	0.40–0.78
Specificity	0.80	0.87	0.80
95% CI	0.74–0.86	0.60–0.98	0.73–0.86
Positive predictive value	0.59	0.92	0.45
Negative predictive value	0.86	0.59	0.90
Positive likelihood ratio	3.4	5.5	3.2
Negative likelihood ratio	0.40	0.31	0.45

Table 5. Microbiological findings in 67 PJI cases according to the type of diagnostic specimen

	Positive periprosthetic tissue cultures (≥ 2) (n = 67)	Positive sonicate fluid cultures (n = 37)
Coagulase-negative staphylococci	30	17
Anaerobes	14	2
Staph. aureus	7	5
Gram-positive cocci	6	5
Gram-negative rods	6	5
Streptococci	4	3