The diagnostic protocol for evaluation of periprosthetic joint infection

Worrying Presence of Asymptomatic Bacterial Colonisation on Implanted Orthopedic Devices

Background Bacterial infection after hardware implantation in orthopedic and trauma surgery is devastating, resulting in increased hospital costs and stays, multiple revision surgeries, and prolonged use of antibiotics. The present study aims to determine whether a symbiotic relationship between the human organism and bacteria in hardware implantation may be present, without clinically evident infection. Materials and methods We studied explanted devices for microbiological analysis, using the sonication technique, from patients who underwent surgical removal of musculoskeletal hardware for mechanical reasons. None of the patients included in the study had clinical or biochemical signs of infection. Results Forty-nine patients were enrolled. Cultures tested positive for bacteria in 42.8% of the 49 patients (21 of 49). In 13 patients, Gram-positive bacteria were isolated, while Gram-negative bacteria were isolated from nine patients. The most frequent bacterial species found was Pseudomonas aeruginosa, with six positive cultures (28.5%). Coagulase-negative staphylococci were isolated from ten implants (47%). Conclusion A pacific coexistence between humans and bacteria is possible following the implantation of metallic devices for trauma or orthopedic ailments. It is still unclear how strong or unstable this equilibrium is.

Detection of bacteria with molecular methods in prosthetic joint infection: sonication fluid better than periprosthetic tissue

Background and purpose - The correct diagnosis of prosthetic joint infection (PJI) can be difficult because bacteria form a biofilm on the surface of the implant. The sensitivity of culture from sonication fluid is better than that from periprosthetic tissue, but no comparison studies using molecular methods on a large scale have been performed. We assessed whether periprosthetic tissue or sonication fluid should be used for molecular analysis. Patients and methods - Implant and tissue samples were retrieved from 87 patients who underwent revision operation of total knee or total hip arthroplasty. Both sample types were analyzed using broad-range (BR-) PCR targeting the 16S rRNA gene. The results were evaluated based on the definition of periprosthetic joint infection from the Workgroup of the Musculoskeletal Infection Society. Results - PJI was diagnosed in 29 patients, whereas aseptic failure was diagnosed in 58 patients. Analysis of sonication fluid using BR-PCR detected bacteria in 27 patients, whereas analysis of periprosthetic tissue by BR-PCR detected bacteria in 22 patients. In 6 of 7 patients in whom BR-PCR analysis of periprosthetic tissue was negative, low-virulence bacteria were present. The sensitivity and specificity values for periprosthetic tissue were 76% and 93%, respectively, and the sensitivity and specificity values for sonication fluid were 95% and 97%. Interpretation - Our results suggest that sonication fluid may be a more appropriate sample than periprosthetic tissue for BR-PCR analysis in patients with PJI. However, further investigation is required to improve detection of bacteria in patients with so-called aseptic failure.

Does Preoperative Antimicrobial Prophylaxis Influence the Diagnostic Potential of Periprosthetic Tissues in Hip or Knee Infections?

BACKGROUND

Undiagnosed low-grade prosthetic joint infections (PJI) are recognized as an important reason for early failure of presumably aseptic revisions. Preoperatively administered antimicrobial prophylaxis reduces the incidence of PJI but it may reduce the sensitivity of microbiologic periprosthetic tissue cultures and consequently increase the incidence of undiagnosed septic prosthetic joint failures, which can lead to catastrophic serial revisions.

QUESTIONS/PURPOSES

We wished to determine whether administration of preoperative antibiotics decreases the likelihood of diagnosing PJI in patients undergoing revision hip or knee arthroplasty in whom infection is suspected.

METHODS

We prospectively enrolled and evaluated 40 patients (29 with THAs and 11 with TKAs) who met the following inclusion criteria: older than 18 years, with suspected PJI of unknown cause, undergoing surgical revision. After arthrotomy, three tissue samples were obtained for microbiologic analysis and diagnosis, and antimicrobial prophylaxis (cefazolin 2 g intravenously) then was administered. Later during the procedure, but before débridement and irrigation, the second set of three tissue samples was obtained from the same surgical area and was cultured. Tissue concentration of prophylactic antibiotic was verified with the second set of samples. A positive culture result was defined as one or more positive cultures (growth on agar at or before 14 days). We then compared the yield on the microbiologic cultures obtained before administration of antibiotics with the yield on the cultures obtained after antibiotics were administered. An a priori analysis was performed; with the numbers available, we had 98% power to detect a difference in diagnostic sensitivity of 33%.

RESULTS

With the numbers available, we found no difference in the likelihood that an infection would be diagnosed between the samples obtained before and after administration of antimicrobial prophylaxis (odds ratio [OR] for positive microbial culture = 0.99; 95% CI, 0.40-2.48; p = 0.99). All measured tissue concentrations of cefazolin were greater than the minimum inhibitory concentration, therefore we found that antibiotic prophylaxis was adequate at the time of second-set tissue specimen recovery.

CONCLUSIONS

Results from this small, prospective series suggest that preoperative antimicrobial prophylaxis may be administered safely even in patients undergoing revision hip or knee arthroplasty in which microbiologic sampling is planned without compromising the diagnostic sensitivity of tissue sample cultures. However, before applying our results more generally, our findings need to be confirmed in larger, multicenter studies that would allow evaluation by sex, procedure, bacteriology, and other potentially important factors.

LEVEL OF EVIDENCE

Level I, diagnostic study.

Prosthesis failure within 2 years of implantation is highly predictive of infection

BACKGROUND

The outcome of revision surgery depends on accurate determination of the cause of prosthesis failure because treatment differs profoundly among aseptic loosening, mechanical failure, and prosthetic joint infections (PJI).

QUESTIONS/PURPOSES

We sought to determine (1) the predictive role of the interval from primary to revision surgery in determining the reason for prosthesis failure of a hip, knee, shoulder, or elbow arthroplasty, and (2) whether positive cultures during revision surgery for aseptic loosening were associated with shorter event-free survival of the prosthesis.

METHODS

All patients undergoing revision surgery between July 2010 and January 2012 were included in a prospective cohort of 112 patients, and were classified as having had failure from aseptic loosening (56%), mechanical failure (15%), or PJI (29%). To make the diagnosis of PJI, at surgery we used a standardized enhanced diagnostic approach in all patients including sampling of five periprosthetic tissue specimens, sonication of removed prosthetic components, prolonged incubation of aerobic and anaerobic cultures, and multiplex PCR of sonication fluid in aseptic loosening cases. Kaplan-Meier survival and Cox proportional hazards regression analysis were performed.

RESULTS

The median time from primary to revision surgery was (p < 0.001) longer for patients with aseptic loosening (7.8 years) than for patients with mechanical failure (1.6 years) or PJI (2 years). No difference in the time to revision was observed for patients with aseptic loosening with positive or negative microbiological cultures (p = 0.594). Propionibacterium acnes was cultured below the established microbiological criteria for positivity in 12 (19%) procedures that had been presumed to have been revisions for aseptic loosening.

CONCLUSIONS

PJI should be considered in all revisions performed within 2 years of implantation even in the absence of clinical or laboratory findings suggestive for infection. However, the growth of low-virulence microorganisms below the cut-off in revisions for apparent aseptic loosening is not associated with early prosthesis failure.