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Current Testing Conventions for Periprosthetic Joint Infection Need Updating, Say Researchers

New research from the Rothman Institute at Jefferson in Philadelphia, Pa., suggests that conventional methods for diagnosing periprosthetic joint infection (PJI) may need some tweaking to improve accuracy. A 2008 article published in Clinical Orthopaedics and Related Research called PJI one of the most challenging complications of joint arthroplasty. The infection can be found deep inside the joint prosthesis after joint replacement surgery.

The Rothman Institute’s Javad Parvizi, M.D., along with his colleagues, is at the forefront of studies aimed at finding a solution to PJI, which can be deadly. Their most recent work has attempted to determine the optimal thresholds for two common biomarkers for systemic inflammation and infection. The data was presented March 21 at the American Association of Orthopedic Surgeons (AAOS) annual meeting in Chicago, Ill.

According to researchers, previous studies concluded that testing blood for elevated levels of C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), known biomarkers for systemic inflammation and infection, was an accurate way of diagnosing an infection. However, levels of ESR and CRP that should sound the infection alarm have been inconsistent, particularly in regard to a new, industry-wide agreed upon definition for PJI.

The new definition for PJI was proposed by a group of researchers from the Musculoskeletal Infection Society in a 2011 Clinical Orthopaedics and Related Research article. Based on the proposed criteria, “definite” PJI would exist if four certain conditions were met; if less than four conditions existed, PJI could “possibly” be present. Some of the conditions include sinus tract communicating with the prosthesis; isolation of a pathogen by culture from at least two separate tissue or fluid samples from the affected prosthetic joint; and an elevated synovial leukocyte count.

The team at Rothman retrospectively reviewed 1,993 patients who underwent revision surgery for aseptic failure (1,095 hips, 594 knees) or PJI (112 hips, 192 knees) between 2000 and 2009. Patients with comorbidities that could elevate the serum inflammatory markers were disqualified from the study. Analysis was performed to determine the optimal threshold and test characteristics for ESR and CRP in hips and knees separately. The study found the real threshold for these tests is higher than previously thought. In addition, researchers found a difference between the knee and hip with regard to the extent these inflammatory markers are elevated with PJI.

The study confirmed the utility of ESR and CRP as a combination test in PJI diagnosis in a large cohort at a single institution. “The findings suggest conventional thresholds for these inflammatory markers may need to be refined to improve their accuracy in diagnosing PJI,” said Parvizi.

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