Alpha-Defensin Offers Limited Utility in Work-Up Prior to Reimplantation in Chronic Periprosthetic Joint Infection in Total Joint Arthroplasty Patients

BACKGROUND

Alpha-defensin (AD) is a synovial biomarker included in the 2018 consensus criteria for diagnosing periprosthetic joint infection (PJI). Its value in assessing eradication of infection prior to second stage reimplantation is unclear. The purpose of this study was to evaluate the impact of AD on eligibility for reimplantation following resection for chronic PJI.

METHODS

This study included patients who previously underwent resection arthroplasty for PJI. Synovial fluid aspirated from 87 patients was retrospectively reviewed. All patients completed a 6-week course of intravenous antibiotics and an appropriate drug holiday. Synovial white blood cell count, percentage neutrophils, and culture from the AD immunoassay laboratory were reviewed with serum erythrocyte sedimentation rate and C-reactive protein values from our institution. A modified version of the 2018 consensus criteria was used, including white blood cell count, percentage neutrophils, erythrocyte sedimentation rate, and C-reactive protein. AD was then added to determine if it changed diagnosis or clinical management.

RESULTS

Four patients were categorized as "infected" (score >6), none exhibited a positive AD or positive culture. Sixty eight patients were diagnosed as "possibly infected" (score 2 to 5), none had a positive AD, and one had a positive culture (Cutibacterium acnes). AD did not change the diagnosis from "possibly infected" to "infected" in any case or alter treatment plans. Fifteen patients had a score of <2 (not infected) and none had a positive AD.

CONCLUSION

The routine use of AD in the work-up prior to a second-stage arthroplasty procedure for PJI may not be warranted.

Alpha-Defensin Is Not Superior to Traditional Diagnostic Methods for Detection of Periprosthetic Joint Infection in Total Hip Arthroplasty and Total Knee Arthroplasty Patients

BACKGROUND

Synovial fluid alpha-defensin (AD) may improve diagnostic accuracy of periprosthetic joint infection (PJI) following total knee (TKA) and hip (THA) arthroplasty but is only available as send-out test. This study evaluated laboratory result accuracy between send-out test vs hospital labs and if AD made a difference in treatment plan.

METHODS

A retrospective review was performed of 152 consecutive patients with a TKA or THA joint aspiration for painful or clinically concerning joint. Synovial fluid was sent to our institution (hospital-based labs, HBL) and send-out immunoassay laboratory (Synovasure). Patients were scored with specific criteria from validated scoring system for PJI using HBL and Synovasure results. The score with and without AD test was compared to determine if AD impacted patient management.

RESULTS

Overall, there was strong agreement between institutions for PJI diagnosis (Cohen's kappa score 0.96). Twenty-nine patients had PJI diagnosis (score ≥6), of which 28 (97%) had positive AD with 1 false-negative result. Sixty-three patients had inconclusive score (between 2 and 5) and 60 patients had negative PJI diagnosis (score ≤1). Of these patients, 5 underwent surgery for infection. Two patients had surgery for positive AD, 2 for positive culture, and 1 because of elevated HBL results. The AD test changed the PJI diagnosis and influenced decision for surgery in only 1.3% (2/152) of patients.

CONCLUSION

Minimal differences were found in laboratory values between institutions. The addition of AD may be useful in cases of equivocal laboratory results but does not appear to be necessary for routine diagnosis of PJI after TKA/THA.

LEVEL EVIDENCE

Level III.

Accuracy of the α-defensin lateral flow assay for diagnosing periprosthetic joint infection in Asians

OBJECTIVE

This study aimed to test the accuracy of the Synovasure®, α-defensin lateral flow test kit, in diagnosing periprosthetic joint infections (PJIs) in a predominantly Asian population and to evaluate whether other patient or disease factors may affect its results.

METHODS

61 Asian patients comprising 70 hip or knee prosthetic joints, performed between November 2015 and November 2018, were retrospectively evaluated. Cases were categorized as infected or not infected using Musculoskeletal Infection Society (MSIS) Criteria. Synovial fluid was tested for α-defensin using a commercially available kit. .

RESULTS

The Synovasure test had a sensitivity of 73.7% (95% confidence interval (CI): 48.8-90.9%) and specificity of 92.2% (95% CI: 81.1-97.8%) in an Asian population, which was slightly lower compared to previously reported studies in a predominantly Caucasian population. The positive predictive value was 77.8% (95% CI: 56.8-90.3%) and the negative predictive value was 90.4% (95% CI: 81.5-95.2%). The test had an area under curve (AUC) of the receiver operating characteristic (ROC) graph of 0.938, which represents an accuracy that is similar to synovial white blood cells (WBCs) and almost equivalent to that of synovial polymorphonuclear cells (PMNs). The presence of diabetes ( p = 0.26), systemic inflammatory joint disease ( p = 0.33), other metallic implants ( p = 0.53), immunosuppression ( p = 0.13), prior antibiotic usage ( p = 0.99), and chronicity of symptoms ( p = 0.34) was not significantly associated with a positive test in patients with PJI.

CONCLUSION

The α-defensin lateral flow test kit is highly accurate in the diagnosis of PJI but with slightly lower sensitivity and specificity in an Asian population when compared with previous studies. The test should be used in conjunction with other MSIS criteria to provide clinically relevant and meaningful results for the diagnosis of PJI.