Tag Archive | alpha defensin

What’s New in Musculoskeletal Infection 2019

Every month, JBJS publishes a review of the most pertinent and impactful studies published in the orthopaedic literature during the previous year in 13 subspecialties. Click here for a collection of all OrthoBuzz Specialty Update summaries.

This month, Thomas K. Fehring, MD, co-author of the July 17, 2019 What’s New in Musculoskeletal Infection,” selected the five most clinically compelling findings—all focused on periprosthetic joint infection (PJI)—from among the more than 90 noteworthy studies summarized in the article.

Preventive Irrigation Solutions
–An in vitro study by Campbell et al.1 found that the chlorine-based Dakin solution forms potentially toxic precipitates when mixed with hydrogen peroxide and chlorhexidine. The authors recommend that surgeons not mix irrigation solutions in wounds during surgery.

PJI Diagnosis
–A clinical evaluation by Stone et al. showed that alpha-defensin levels in combination with synovial C-reactive protein had high sensitivity for PJI diagnosis, but the alpha-defensin biomarker can lead to false-positive results in the presence of metallosis and false-negative results in the presence of low-virulence organisms.

–In an investigation of next-generation molecular sequencing for diagnosis of PJI in synovial fluid and tissue, Tarabichi et al. found that in 28 revision cases considered to be infected, cultures were positive in only 61%, while next-generation sequencing was positive in 89%. However, next-generation sequencing also identified microbes in 25% of aseptic revisions that had negative cultures and in 35% of primary total joint arthroplasties. Identification of pathogens in cases considered to be aseptic is concerning and requires further research.

Treating PJI
–A multicenter study found that irrigation and debridement with component retention to treat PJI after total knee arthroplasty had a failure rate of 57% at 4 years.2

–Findings from an 80-patient study by Ford et al.3 challenge the assumption that 2-stage exchanges are highly successful. Fourteen (17.5%) of the patients in the study never underwent reimplantation, 30% had a serious complication, and of the 66 patients with a successful reimplantation, only 73% remained infection-free. Additionally 11% of the patients required a spacer exchange for persistent infection.

References

  1. Campbell ST, Goodnough LH, Bennett CG, Giori NJ. Antiseptics commonly used in total joint arthroplasty interact and may form toxic products. J Arthroplasty.2018 Mar;33(3):844-6. Epub 2017 Nov 11.
  2. Urish KL, Bullock AG, Kreger AM, Shah NB, Jeong K, Rothenberger SD; Infected Implant Consortium. A multicenter study of irrigation and debridement in total knee arthroplasty periprosthetic joint infection: treatment failure is high. J Arthroplasty.2018 Apr;33(4):1154-9. Epub 2017 Nov 21.
  3. Ford AN, Holzmeister AM, Rees HW, Belich PD. Characterization of outcomes of 2-stage exchange arthroplasty in the treatment of prosthetic joint infections. J Arthroplasty.2018 Jul;33(7S):S224-7. Epub 2018 Feb 17.

FDA Approves Rapid Alpha-Defensin Test for PJI

The US FDA has approved the Synovasure Alpha Defensin Lateral Flow Test Kit for helping detect periprosthetic joint infection (PJI) in the synovial fluid of patients being evaluated for revision joint replacement.

Alpha defensins are proteins released by neutrophils in early response to infection. OrthoBuzz previously summarized a 2018 JBJS study that found this rapid alpha defensin test to have 96.9% overall accuracy.

In the FDA news release about the approval, Tim Stenzel, MD, director of the FDA’s Office of In Vitro Diagnostics and Radiological Health, said the test provides health care professionals with additional information that “could potentially reduce patient risk by avoiding unnecessary revision operations for replacement joints.”

In a Commentary on the 2018 JBJS study, Garth Ehrlich, PhD and Michael Palmer, MD said the device is a “substantive advance,” but not “a panacea.” For one thing, metallosis would still need to be ruled out with MRI, because that noninfectious etiology triggers a false-positive result with this rapid test. Synovasure is also likely to miss detection of slow-growing, chronic bacterial pathogens such as Proprionibacterium acnes, the commentators said.

The Synovasure test kit received approval through the FDA’s de novo premarket pathway, which is reserved for “low- to moderate-risk devices of a new type,” according to the agency.

Rapid Alpha Defensin Test Helpful for Diagnosing PJI

Synovasure for OBuzzQuick and accurate: that’s what orthopaedic surgeons want in diagnostic tools to help them determine whether patients presenting with pain after total joint arthroplasty have an infection. A prospective Level I study by Gehrke et al. in the January 3, 2018 issue of The Journal of Bone & Joint Surgery determined that a new lateral flow version of the Synovasure Alpha Defensin Test meets those requirements.

Alpha defensin is a protein secreted by neutrophils in response to bacterial infection, prior to the development of specific immune responses. Earlier research established alpha defensin in synovial aspirates to be an excellent biomarker for periprosthetic joint infection (PJI). The original ELISA-based alpha defensin test is usually sent out for 24-hour processing, limiting its intraoperative utility. However, the lateral flow version of the test (akin to an over-the-counter pregnancy test) was approved for use in Europe—and its results are available in 10 to 15 minutes.

Gehrke et al. compared the rapid test’s results to the diagnostic criteria promulgated by the Musculoskeletal Infection Society (MSIS). According to MSIS criteria, there were 76 joints with PJI among 191 study subjects on whom 195 joint aspirations were performed. Using that as the benchmark for diagnosis, the authors analyzed results from the rapid alpha defensin tests and found the following performance:

  • 92.1% sensitivity
  • 100% specificity
  • 100% positive predictive value
  • 95.2% negative predictive value
  • 96.9% overall accuracy

Although the rapid test does not provide information about the identity of specific pathogens, the authors conclude that it “enables surgeons to start proper therapy without delay.” That ability comes at a price, however. In Germany, where this study was performed, each rapid test costs about 400 Euros, which is nearly $500 US.

In a commentary on the study, Garth Ehrlich and Michael Palmer cite another possible cost with the rapid-test scenario. Prior to using any alpha defensin test, physicians must rule out metallosis with MRI, because that non-infectious entity triggers false-positive results.