Editor’s note: The following content was published in the AAOS Now Special Edition and distributed in June 2020. The content was originally scheduled for the AAOS Now Daily Edition, which publishes each year onsite at the AAOS Annual Meeting but this year’s meeting in March was canceled due to COVID-19. Despite the cancellation, members can access virtual content from the Annual Meeting by visiting the Academy’s Annual Meeting Virtual Experience webpage.

Carl Deirmengian, MD, FAAOS, began his medical education and career at a time when his interest in genomics presented both a challenge and an opportunity. The opportunity would lead to a 15-year body of work studying synovial fluid that resulted in the first Food and Drug Administration (FDA)-authorized diagnostic test for periprosthetic joint infection (PJI) specifically intended for orthopaedics.

Dr. Deirmengian, orthopaedic surgeon and associate professor of orthopaedic surgery at the Rothman Orthopaedic Institute in Philadelphia, received this year’s Kappa Delta Elizabeth Winston Lanier Award.

“When I began my residency, the genomic revolution was happening, and there were interesting genome experiments; however, there wasn’t much opportunity to study genomics for orthopaedics,” recalled Dr. Deirmengian.

“I remember the first time I saw synovial fluid and the uncertainty of knowing if it was infected or not,” said Dr. Deirmengian. “However, when I saw that synovial fluid was basically all white blood cells, I knew it was a perfect tissue to study at a genomic level because of its homogenous nature. The idea of having a test for joint infection that was made for orthopaedics and delivered a positive or negative result made a lot of sense because the tests we use to diagnose infection traditionally require converting a raw value into an interpretation that is not specific to arthroplasty.”

Current tests, such as the Musculoskeletal Infection Society (MSIS) criteria-based system, have established ideal “arthroplasty-specific” cutoffs for tests, including erythrocyte sedimentation rate, C-reactive protein, synovial leukocyte count, and neutrophil percent.

“From a public health and standardization perceptive, it’s concerning that different institutions and authoritative bodies have chosen different ‘arthroplasty-specific’ cutoffs for these traditional tests,” said Dr. Deirmengian. “There’s complexity having to know all of the MSIS or International Consensus Meeting cutoffs and their application. This requires practicing surgeons to ignore their laboratory’s test result interpretation, and instead apply the recommended threshold, which may not be systematically performed in a proper manner.”

With these challenges and ideas for discovery, Dr. Deirmengian began a progressive journey at one of the most basic levels––genetic biomarkers.

Knowing neutrophils

Dr. Deirmengian theorized that there had to be something in the joint responding to infection. At that time, there was a consensus that neutrophils were a canned response to inflammation.

By using new genomic tools to study the microarray, Dr. Deirmengian published his first report in 2005, which identified potential synovial fluid biomarkers for PJI. Specific genomic pathways—including the interleukin, tumor necrosis, and antimicrobial peptide pathways—were identified as potential sources for a diagnostic biomarker of PJI.

Finding the optimal protein biomarker

The relative levels of 23 different proteins were measured in the synovial fluid of patients with PJI versus aseptic loosening. It was discovered that many synovial fluid biomarkers had excellent diagnostic performance, including those in the interleukin and antimicrobial peptide pathways, verifying the finding suggested by the initial genomic study.

As a result, Dr. Deirmengian was the first to demonstrate that different families of synovial fluid protein biomarkers can be utilized to potentially diagnose PJI, initiating this field of discovery and leading to an increase in literature focusing on the use of biomarkers to detect PJI (Fig. 1).

Dr. Deirmengian then partnered with a former representative from a medical device company, Mike Behr, to form a small company and joined the incubator at Main Line Health, the Lankenau Institute for Medical Research in Wynnewood, Pa., all with funding from family, friends, and a handful of seed investors. From there, Dr. Deirmengian and his team became the first to identify that the alpha-defensins have ideal concentrations, stability, and binding characteristics and could lead to the development of a standardized synovial fluid test for PJI.

How do we prove this to the world?

Dr. Deirmengian and his team started a diagnostic orthopaedics lab to offer the alpha-defensin and other tests to orthopaedic surgeons. It quickly became one of the largest laboratories in the world, receiving hundreds of synovial fluid samples a week, which allowed them to conduct more extensive research.

Dr. Deirmengian explained, “Having this lab not only increased our sample number, it made our evaluations more robust because we had data on every sample. This is a very unique situation to be in from a research perspective. I don’t know of any other situation where a laboratory has such a high volume of synovial fluid samples and accompanying data on other laboratory results.”

With a successful lab and business, augmented by Chief Executive Officer Rick Birkmeyer, PhD, the team wanted a partner who could help guide them through FDA clearance. Zimmer Biomet assumed that role and eventually bought the company. “I know in an ideal world, you’d imagine that you could make significant medical advancements without a conflict of interest,” said Dr. Deirmengian. “However, it would have been impossible without this partnership. At some point, it becomes necessary to include a corporate partner in the translation of research to a product that performs well in clinical practice.”

As other institutional studies confirmed the work of the team, the next step was to take the alpha-defensin test through the FDA review process. This included a prospective, multicenter, adjudicator-blinded clinical trial. The primary purpose of the study was to evaluate the clinical performance of the Alpha-defensin Lateral Flow Test for PJI, including sensitivity and specificity. A secondary goal was to compare the performance of the Alpha-defensin Lateral Flow Test to the Alpha-defensin Laboratory-based Immunoassay.

The study included 305 adults (mean age, 64.8 years; 174 were women) with a total hip or knee arthroplasty exhibiting signs and symptoms that demonstrated a likely need for revision arthroplasty.

Among the results of the study:

• The test yielded an Alpha-defensin Lateral Flow Test sensitivity of 89.5 percent and a specificity of 94.8 percent (Table 1).
• After exclusion of patients who had a synovial fluid sample with >1,000,000 red blood cell count per μL (n = 17), representing gross blood, the Alpha-
  defensin Lateral Flow Test yielded a sensitivity of 94.3 percent and a specificity of 94.5 percent (Table 1).
• The study verified previous findings, including (Table 2):
  • The antibiotic treatment of patients did not appear to affect Alpha-defensin Lateral Flow Test’s diagnostic performance, despite the significant effect of antibiotics on the performance of other traditional tests in the literature.
  • There was no significant difference in the diagnostic performance of the Alpha-defensin Lateral Flow Test on patients with systemic inflammatory disease (or in the setting of culture-negative versus culture-positive PJI).
• A comparison of the sensitivity of the Alpha-defensin Lateral Flow Test to the Alpha-defensin Laboratory-based Immunoassay did not demonstrate a statistically significant difference (94.3 percent versus 92.7 percent; P > 0.05).
• A comparison of the specificity of the Alpha-defensin Lateral Flow Test to the Alpha-defensin Laboratory-based Immunoassay did not demonstrate a statistically significant difference (94.8 percent versus 97.6 percent; P > 0.05).

In May 2019, the FDA authorized the Alpha-defensin Lateral Flow Test as an aid for the detection of PJI. Prior to the authorization, there were no FDA-
authorized diagnostic tests specifically designed to help healthcare professionals determine whether the inflammation around a prosthetic joint was due to an infection or another cause.

Dr. Deirmengian noted, “There’s value in having a test that is intended for orthopaedics to diagnose PJI, as every surgeon, regardless of subspecialty, training, or knowledge, can be equally effective in using the test and understanding its result. I’m hopeful that this study will provide a pathway for improved diagnostic tools in our field.”

Jennifer Lefkowitz is a freelance writer for AAOS Now.

References 

1. Deirmengian C, Lonner JH, Booth RE, Jr: The Mark Coventry Award: white blood cell gene expression: a new approach toward the study and diagnosis of infection. Clin Orthop Relat Res 2005;440:38-44.
2. Deirmengian C, Hallab N, Tarabishy A, et al: Synovial fluid biomarkers for periprosthetic infection. Clin Orthop Relat Res 2010;468:2017-23.
3. Deirmengian C, Kardos K, Kilmartin P, et al: Diagnosing periprosthetic joint infection: has the era of the biomarker arrived? Clin Orthop Relat Res 2014;472:3254-62.
4. Shahi A, Parvizi J, Kazarian GS, et al: The alpha-defensin test for periprosthetic joint infections is not affected by prior antibiotic administration. Clin Orthop Relat Res 2016;474:1610-5.
5. Food and Drug Administration: FDA permits marketing of first diagnostic test to aid in detecting prosthetic joint infections. Available at: https://www.fda.gov/news-events/press-announcements/fda-permits-marketing-first-diagnostic-test-aid-detecting-prosthetic-joint-infections. Accessed January 27, 2020.