TESTING TRENDS

Search Intensifies for Markers for Prosthetic Joint Infection

Nearly one million total hip arthroplasties and total knee arthroplasties are performed in the United States each year, a number that is expected to continue to increase for decades given the aging of the population and increases in body mass index.

Prosthetic joint infection (PJI) is one of the most dreaded complications following arthroplasty surgery and is the leading cause of implant failure and costly revision surgery, with PJI rates estimated at up to 1 percent for hip and shoulder replacements and up to 2 percent in knee replacements. Yet, there is no definitive test for PJI, as most laboratory tests are indirect measures of infection.

Painful joint history and physical exam remain the primary diagnostic tools. However, much research is currently happening, searching for specific markers of PJI. DTET examined recent studies of promising markers associated with PJI.

Protein Markers In Synovial Fluid May Diagnose, Provide Ongoing Monitoring of PJI
Interleukin (IL)-16, IL-18, and cysteine-rich with EGF-like domains 2 (CRELD2) are potential biomarkers for PJI diagnosis, according to a study published in the April issue of Bone & Joint Research. Tests of these markers in synovial fluid outperformed blood tests and may be useful for follow-up monitoring of PFJI to assess the success of debridement, the authors say.

Analysis included 48 patients (including 39 PJI and nine aseptic loosening case controls) who required knee or hip revision surgery between January 2016 and December 2017. Synovial fluid and blood samples were analyzed by protein microarray and enzyme-linked immunosorbent assay to compare protein expression patterns among patients with aseptic loosening and PJI. C-reactive protein level and leucocyte numbers were also assessed.

The researchers report that with cut-off values of 1,473 pg/ml, 359 pg/ml, and 8.45 pg/ml were established for IL-16, IL-18, and cysteine-rich with EGF-like domains 2 (CRELD2), respectively. Receiver operating characteristic curve analysis showed that these markers showed excellent accuracy as predictors of PJI, with an area of 1. Like plasma CRP concentration and blood leucocyte number, IL-16, IL-18, and CRELD2 levels returned to their respective baseline values following the completion of debridement, suggesting them as potential biomarkers for determining the timing of prosthesis reimplantation.

“Based on the findings of this study and future diagnostic trends, we believe that single-molecule-based diagnosis [for PJI] is inadequate,” write the authors led by M-F. Chen, Ph.D., from Chang Gung Memorial Hospital in Taiwan. “A scoring system using multiple factors for PJI diagnosis would be optimal. Although the establishment of such a scoring system requires continued efforts to perform marker evaluation, the identification of IL-16, IL-18, and CRELD2 as diagnostic markers for PJI and successful debridement in this study represents a promising first step in the process.”

Sequencing Can Speed Definitive Infection Diagnosis
Metagenomic sequencing can successfully identify the cause of PJI, according to presentation at the European Congress of Clinical Microbiology and Infectious Diseases (April 13-16; The Netherlands). The culture-free method uses DNA isolated directly from the clinical sample and can provide results in hours rather than the five to 10 days needed with current gold standard of cultures of periprosthetic tissue samples collected during surgery.

The researchers from University of Oxford in the United Kingdom sought to improve the microbiological diagnosis of infections associated with orthopedic devices using whole-genome sequencing technologies in order to achieve faster, more sensitive results, with the ultimate goal of improving antibiotic stewardship and patient outcomes.

The researchers report that they initially started using the Illumina MiSeq platform. Sequencing took approximately 2.5 days and required at least 1,150 reads for an individual species or at least 125 reads for an individual species if the at least 15 percent of the total bacterial reads belonged to same species. Species-level sensitivity and specificity was 88 percent. However, the researchers learned that human DNA was “problematic” with human DNA accounting for more than 90 percent of reads in 97 percent of samples. Further, the researchers determined more reads are needed in order to determine the organisms’ antimicrobial sensitivity.

The researchers next adopted nanopore sequencing technology, which offered the benefits of being portable, having long read lengths, and providing real-time analysis. The so-called CRuMPIT (Clinical Real-time Metagenomics Pathogen Identification Test) relies upon a redesigned workflow that involves removing surgical removal of a prosthetic implant and then placing it in saline and sonicating it to obtain approximately 40 mL of sonication fluid, which is essentially the largest volume easily handled in the laboratory. This approach maximizes the number of cells DNA can be extract from. Following extraction, the DNA is then cleaned, prepared into libraries, and sequenced. Findings show that the methodology enables sequencing of near-whole genomes and antimicrobial resistance can be determined within hours of surgery.

Diagnosis of Joint Infection in Patients With Inflammatory Disease
Alpha-defensin can accurately diagnose PJI even in patients with systemic inflammatory disease undergoing revision total hip or knee arthroplasty, according to a study published April 13 in the Journal of Arthroplasty.

Measuring alpha-defensin concentrations in synovial fluid is increasingly used to test for PJI in conjunction with other laboratory tests, however, the use of inflammatory markers (e.g., C-reactive protein, erythrocyte sedimentation rate, and white blood cell counts) has been questioned, particularly in patients with inflammatory diseases (e.g., rheumatoid arthritis, psoriatic arthritis, and sarcoidosis).

Researchers from the Cleveland Clinic (Ohio) retrospectively reviewed 1,374 cases who underwent revision total hip or knee arthroplasty at a single healthcare system from 2014 to 2017. Analysis included 41 cases with rheumatologist-diagnosed inflammatory diseases (17 with rheumatoid arthritis, seven with psoriatic arthritis, five with ulcerative colitis, six with polymyalgia rheumatica, three with sarcoidosis, one with polymyositis, one with systemic lupus erythematosus, and one with systemic sclerosis). All patients with available preoperative alpha-defensin results were included. The laboratory-based immunoassay for alpha-defensin (Synovasure; CD Diagnostics) was performed on synovial fluid. Three to five samples were taken from patients undergoing a one-stage revision arthroplasty, the first stage of two-stage revision arthroplasty, or irrigation and debridement and samples were cultured for seven to 14 days.

The alpha-defensin test demonstrated a sensitivity of 93 percent, a specificity of 100 percent, a positive predictive value of 100 percent, a negative predictive value of 96 percent, and an overall accuracy of 97 percent for diagnosing PJI. There was one false-negative result in a patient with polymyositis.

“As a relatively new marker for diagnosing PJI, alpha-defensin has been widely reported to have excellent diagnostic accuracy in diagnosing PJI,” write the authors led by Yushi Miyamae, M.D., Ph.D. “To our knowledge, this was the first study to analyze the utility of laboratory-based alpha-defensin exclusively for patients with inflammatory diseases, and the results of our study confirmed the diagnostic accuracy for diagnosing PJI, even in patients with inflammatory diseases, with no false-positive result.”

Markers May Predict Which Patients Need Knee Replacement
CTX-I (C-telopeptide of crosslinked collagen type I), a marker of bone resorption, and CTX-II (C-telopeptide of crosslinked collagen type II), a potential marker of cartilage degradation, may predict joint failure among patients with osteoarthritis, according to a study published April 15 in a supplement to Osteoarthritis and Cartilage, highlighting abstracts resented at the 2019 Osteoarthritis Research Society International’s World Congress on Osteoarthritis (May 2-5; Toronto). Specifically, serum CTX-I and urinary CTX-II levels at baseline were associated with increased risk of undergoing knee or hip replacement surgery over two years of follow-up.

Based on post-hoc analysis using data from two clinical trials investigating oral salmon calcitonin in osteoarthritis in more than 1,300 patients, 27 total joint replacements of the knee or hip were reported.

Researchers from University Health Network in Toronto, Canada found that at baseline, high CTX-II was statistically significantly associated with a 3.08 times higher risk of undergoing joint replacement during the study period, and 8.94 times higher risk of specifically knee arthroplasty. Similarly, high sCTX-I was statistically significantly associated 3.4 times higher risk of undergoing either knee or hip arthroplasty, but did not reach statistical significance for risk of knee arthroplasty alone.

Takeaway: Given the expected increase in the number of total joint replacements, and accompanying PJIs, there is great interest in discovering objective markers for diagnosis of PJI. These recent studies show promising candidates.

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