Abstract
BackgroundCulturing of the sonication fluid of removed implants has proven to be more sensitive than conventional periprosthetic tissue culture for the microbiological diagnosis of prosthetic joint infection. Since bacteria surviving on antibiotic-loaded cement spacers used in a two-stage exchange protocol for infected arthroplasties may cause the persistence of infection, in this study we asked whether the sonication also could be used to identify bacteria on antibiotic-loaded cement spacers removed at the second surgical stage during a two-stage exchange procedure to confirm whether or not the prosthetic joint infection had been eradicated.MethodsWe cultured the sonication fluid of cement spacers that had been originally implanted in a two-stage exchange protocol in 21 patients (mean age, 66 years) affected by prosthetic joint infection (16 total knee prostheses and 5 hip prostheses). The cement spacers were vortexed for 30 seconds and then subjected to sonication (frequency 35–40 KHz). The resulting sonicate fluid was cultured for aerobic and anaerobic bacteria.ResultsThe sonication fluid culture of the removed spacer was positive in six patients (29%), with isolation of methicillin-sensible Staphylococcus Aureus (MSSA) in three cases, methicillin-resistant Staphylococcus Aureus (MRSA) in one case and Pseudomonas Aeruginosa in two cases. In three of these positive cases, the traditional culture of periprosthetic tissue was negative. Two patients with positive sonication culture of the spacer were successfully treated by early debridement of the revision prosthesis and systemic antibiotic therapy. In three patients a knee arthrodesis was planned and performed as the second surgical stage. In two of them the infection was caused by highly resistant Pseudomonas Aeruginosa. The other patient with a MSSA infection had been poorly compliant with the systemic antibiotic therapy due to her mental impairment. The patient originally affected by MRSA infection of his primary hip arthroplasty developed recurrent infection of his revision prosthesis and eventually underwent Girdlestone arthroplasty.ConclusionsThe sonication culture can be used to discover any bacteria on the antibiotic-loaded cement spacer during a two-stage exchange protocol, thus permitting the adoption of timely treatment options, such as the early prosthetic debridment.
Highlights
Culturing of the sonication fluid of removed implants has proven to be more sensitive than conventional periprosthetic tissue culture for the microbiological diagnosis of prosthetic joint infection
In all cases with positive sonicate fluid culture of the removed spacer, the same pathogen that had caused the initial infection grew in the sonication culture of the cement spacer
Two patients with methicillin-sensible Staphylococcus Aureus (MSSA) infection (Table 1 – patients n. 2 and n. 10) of their spacer were successfully treated by aggressive debridement of the prosthetic joint within 30 days of prosthesis implantation and systemic antibiotic therapy tailored to the sensitivity of the cultures for 3 months
Summary
Culturing of the sonication fluid of removed implants has proven to be more sensitive than conventional periprosthetic tissue culture for the microbiological diagnosis of prosthetic joint infection. High rates of satisfactory outcomes in terms of infection eradication have been reported using the two-stage exchange procedure [1], but in some cases both the clinical picture and serum C-reactive protein (CRP) levels do not normalize over time even with the removal of the infected implant and the prolonged implantation of the antibiotic-loaded cement spacer [2] In these cases, the presence of biofilm-forming pathogens may cause the infection to persist and the antibioticloaded cement itself can act as a biomaterial surface to which bacteria may preferentially adhere, grow and possibly even develop antibiotic resistance [3]. In this study we asked whether the sonication could be used to identify bacteria on antibiotic-loaded cement spacers removed at the second surgical stage during a two-stage exchange procedure, a) to confirm whether or not the PJI had been eradicated and b) to compare the findings from conventional intraoperative tissue cultures with the findings after sonication of the cement spacer
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