Systematic Review of Novel Synovial Fluid Markers and Polymerase Chain Reaction in the Diagnosis of Prosthetic Joint Infection

The American Journal of Orthopedics. 2017 July;46(4):190-198

July 5, 2017 | The American Journal of Orthopedics

Duran Mitchell, BA ; Jose Perez, BS ; Luis Grau, MD ; Spencer Summers, MD ; Samuel Rosas, MD ; Alvin Ong, MD ; Michaela M. Schneiderbauer, MD, MBA ; Victor H. Hernandez, MD, MSc

Prosthetic joint infection (PJI) may be underreported because of difficulty in making a diagnosis, especially in infections with low-virulence organisms. Reports of PJI cases misdiagnosed as aseptic loosening suggest that current screening and diagnostic tools are not sensitive enough to detect all infections and that PJI likely is underdiagnosed. We reviewed the literature on recently developed novel synovial biomarkers and polymerase chain reaction (PCR) technologies, of which several have proved promising as highly sensitive and specific tools for detecting PJI. We followed the recommendations of PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). Of 90 papers screened by title or abstract and then by full text, 15 met our inclusion criteria. Sensitivities reported in the included studies ranged from 63% to 100% for α-defensin, from 46.8% to 90.9% for interleukin 6, from 28.6% to 100% for leukocyte esterase, and from 67.10% to 95.7% for PCR. Specificities ranged from 95% to 100% for α-defensin, from 85.7% to 97.6% for interleukin 6, from 63.6% to 96.5% for leukocyte esterase, and from 12.3% to 97.8% for PCR. α-Defensin is a highly sensitive and specific screening tool that may help improve the accuracy of PJI detection, particularly in low-grade infections.

Polymerase Chain Reaction

Studies have found that PCR analysis of synovial fluid is effective in detecting bacteria on the surface of implants removed during revision arthroplasties. Comparison of the 16S rRNA gene sequences of bacterial genomes showed a diverse range of bacterial species within biofilms on the surface of clinical and subclinical infections.¹⁷ These findings, along with those of other studies, suggest that PCR analysis of synovial fluid is useful in diagnosing PJI and identifying organisms and their sensitivities to antibiotics.

Gallo and colleagues¹⁸ performed a prospective clinical study on 115 patients who underwent revision TKAs or THAs. Synovial fluid was collected intraoperatively. PCR assays targeting the 16S rDNA were carried out on 101 patients. PJIs were classified based on criteria of the authors of this study, of which there were 42. The sensitivity, specificity, PPV, NPV, +LR, and -LR for PCR were 71.4% (95% CI, 61.5%-75.5%), 97% (95% CI, 91.7%-99.1%), 92.6% (95% CI, 79.8%-97.9%), 86.5% (95% CI, 81.8%-88.4%), 23.6 (95% CI, 5.9%-93.8%), and 0.29 (95% CI, 0.17%-0.49%), respectively. Of note the most common organism detected in 42 PJIs was coagulase-negative Staphylococcus.

Marin and colleagues¹⁹ conducted a prospective study of 122 patients who underwent arthroplasty for suspected infection or aseptic loosening as defined by the authors’ clinicohistopathologic criteria. Synovial fluid and biopsy specimens were collected during surgery, and 40 patients met the infection criteria. The authors concluded that 16S PCR is more specific and has better PPV than culture does as one positive 16S PCR resulted in a specificity and PPV of PJI of 96.3% and 91.7%, respectively. However, they noted that culture was more sensitive in diagnosing PJI.

Jacovides and colleagues²⁰ conducted a prospective study on 82 patients undergoing primary TKA, revision TKA, and revision THA.

The synovial fluid aspirate was collected intraoperatively. PJI was diagnosed based on study specific criteria, which was a combination of clinical suspicion and standard laboratory tests (ESR, CRP, cell count and tissue culture). Using the study’s criteria, PJI was diagnosed in 23 samples, and 57 samples were diagnosed as uninfected. When 1 or more species were present, the PCR-Electrospray Ionization Mass Spectrometry (PCR-ESI/MS) yielded a sensitivity, specificity, PPV, and NPV value of 95.7%, 12.3%, 30.6%, and 87.5%, respectively.

The low PCR sensitivities reported in the literature were explained in a review by Hartley and Harris.²¹ They wrote that BR 16S rDNA and sequencing of PJI samples inherently have low sensitivity because of the contamination that can occur from the PCR reagents themselves or from sample mishandling. Techniques that address contaminant (extraneous DNA) removal, such as ultraviolet irradiation and DNase treatment, reduce Taq DNA polymerase activity, which reduces PCR sensitivity.

The simplest way to avoid the effects of “low-level contaminants” is to decrease the number of PCR cycles, which also reduces sensitivity. However, loss of contaminants has resulted in increased specificities in studies that have used BR 16S rDNA PCR. The authors also stated that, when PCR incorporates cloning and sequencing, mass spectroscopic detection, or species-specific PCR, sensitivity is higher with increased contamination.

Table 4 and Figure 5 provide a concise review of the findings of each study.

Discussion

Although there is no gold standard for the diagnosis of PJIs, several clinical and laboratory criteria guidelines are currently used to help clinicians diagnose infections of prosthetic joints. However, despite standardization of diagnostic criteria, PJI continue to be a diagnostic challenge.

Diagnosing PJI has been difficult for several reasons, including lack of highly sensitive and specific clinical findings and laboratory tests, as well as difficulty in culturing organisms, particularly fastidious organisms. More effective diagnostic tools are needed to avoid failing to accurately detect infections which lead to poor outcomes in patients who undergo TJA. Moreover, PJIs with low-virulence organisms are especially troublesome, as they can present with normal serum inflammatory markers and negative synovial fluid analysis and cultures from joint aspiration.²²

AD is a highly sensitive and specific synovial fluid biomarker in detecting common PJIs.

AD has a higher sensitivity and specificity for detecting PJI, as compared to synovial fluid cell count, culture, ESR, and CRP.^15,16,19 Moreover, it has been shown that as many as 38% to 88% of patients diagnosed with aseptic loosening have PJIs with low-grade organisms,^23,24 such as Coagulase-negative S acnes and P acnes. Several studies reviewed in this article have demonstrated that AD can detect infections with these low virulence organisms. Our systematic review supports the claim that AD can potentially be used as a screening tool for PJI with common, as well as difficult-to-detect, organisms.

Our findings also support the claim that novel synovial fluid biomarkers have the potential to become of significant diagnostic use and help improve the ability to diagnose PJIs when combined with current laboratory and clinical diagnostic criteria.

In summary, 5 AD studies^5-9 had sensitivity ranging from 63% to 100% and specificity ranging from 95% to 100%; 3 IL-6 studies^10-12 had sensitivity ranging from 46.8% to 90.9% and specificity ranging from 85.7% to 97.6%; 4 LE studies^13-16 had sensitivity ranging from 28.6% to 100% and specificity ranging from 63.6% to 96.5%; and 3 PCR studies^18-20 had sensitivity ranging from 67.1% to 95.7% and specificity ranging from 12.3% to 97.8%. Sensitivity and specificity were consistently higher for AD than for IL-6, LE, and PCR, though there was significant overlap, heterogeneity, and variation across all the included studies.

Moreover, the outlier study with the lowest sensitivity for AD (63%) was in patients undergoing TSA, where P acnes infection is more common and has been reported to be more difficult to detect by standard diagnostic tools. Tables 5, 6 and Figures 6, 7 provide the data for each of these studies.

Although the overall incidence of PJI is low, infected revisions remain a substantial financial burden to hospitals, as annual costs of infected revisions is estimated to exceed $1.62 billion by 2020.²⁵ The usefulness of novel biomarkers and PCR in diagnosing PJI can be found in their ability to diagnose infections and facilitate appropriate early treatment. Several of these tests are readily available commercially and have the potential to be cost-effective diagnostic tools. The price to perform an AD test from Synovasure^TM (Zimmer Biomet) ranges from $93 to $143. LE also provides an economic option for diagnosing PJI, as LE strips are commercially available for the cost of about 25 cents. PCR has also become an economic option, as costs can average $15.50 per sample extraction or PCR assay and $42.50 per amplicon sequence as reported in a study by Vandercam and colleagues.²⁶ Future studies are needed to determine a diagnostic algorithm which incorporates these novel synovial markers to improve diagnostic accuracy of PJI in the most cost effective manner.

The current literature supports that AD can potentially be used to screen for PJI. Our findings suggest novel synovial fluid biomarkers may become of significant diagnostic use when combined with current laboratory and clinical diagnostic criteria. We recommend use of AD in cases in which pain, stiffness, and poor TJA outcome cannot be explained by errors in surgical technique, and infection is suspected despite MSIS criteria not being met.

The studies reviewed in this manuscript were limited in that none presented level I evidence (12 had level II evidence, and 3 had level III evidence), and there was significant heterogeneity (some studies used their own diagnostic standard, and others used the MSIS criteria). Larger scale prospective studies comparing serum ESR/CRP level and synovial fluid analysis to novel synovial markers are needed.

References

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