Diagnostic Utility and Thresholds for Commonly Obtained Serum and Synovial Markers Prior to Reimplantation in Periprosthetic Joint Infection

Diagnostic and Predictive Efficacy of Synovial Fluid Versus Serum C-Reactive Protein Levels for Periprosthetic Joint Infection and Reimplantation Success

BACKGROUND

A 2-stage exchange revision for periprosthetic joint infection (PJI) is associated with major risks for reinfection. Although serum markers are frequently used for diagnosis, their effectiveness remains debatable. Synovial fluid markers may offer a more accurate diagnosis of PJI; however, the importance of these biomarkers, notably synovial fluid C-reactive protein (syCRP), remains controversial, particularly in the context of reimplantation. The present study aimed to clarify these diagnostic uncertainties by evaluating the diagnostic efficacy of syCRP versus serum CRP (seCRP) levels in the context of PJI and recurring or persisting infections before reimplantation.

METHODS

A total of 186 patients were enrolled and divided into 2 groups: aseptic revision (n = 112) and PJI revision (n = 74). Of the PJI group, 65 were categorized as success and 9 as failure, based on the presence of recurrent or persistent infection before reimplantation. The syCRP and seCRP levels and their changes were assessed preoperatively and in the first-stage and second-stage revisions. Additionally, receiver operating characteristic (ROC) curves and area under the ROC curves (AUCs) were analyzed.

RESULTS

Both seCRP and syCRP levels were significantly elevated in the PJI group compared with the aseptic group (P < .001). The ROC curve analysis highlighted the enhanced diagnostic accuracy of syCRP for PJI, with an AUC of 0.93 versus 0.80 for seCRP. Furthermore, syCRP proved to be more reliable in predicting reimplantation success, exhibiting an AUC of 0.86 versus 0.63 for seCRP. In evaluating trends in CRP levels to determine reimplantation timing, changes in syCRP levels demonstrated superior diagnostic utility, exhibiting an AUC of 0.79 versus 0.63 for changes in seCRP levels.

CONCLUSIONS

In assessing PJI and infections before reimplantation, syCRP may offer enhanced accuracy compared with seCRP. Nevertheless, variations in both syCRP and seCRP levels did not consistently predict the outcome of reimplantation.

How Reliable Is the Absolute Synovial Polymorphonuclear Neutrophil Cell Count in Diagnosing Periprosthetic Joint Infection?

BACKGROUND

Diagnosing periprosthetic joint infection (PJI) is a daunting task for even the most experienced orthopedic surgeons, as there is currently no test available that can provide absolute accuracy. Utilizing an established synovial indicator for detecting PJI without incurring additional costs or resources would be the optimal solution for predicting the presence of infection. Therefore, we hypothesized that synovial absolute neutrophil count (ANC) would improve the diagnostic accuracy of chronic knee and hip PJI.

METHODS

The study included 260 patients (134 men and 126 women, mean age of 70 years [range, 26 to 89]) who underwent aspiration during preoperative workup. Of these, 109 patients (41.9%) were diagnosed with chronic PJI (50 knees, 59 hips), and 151 patients (58.1%) were diagnosed as aseptic (94 knees, 57 hips). Data obtained from all patients included age, sex, procedure type (total hip or total knee arthroplasty), operation side, synovial white blood cell count (cells/μL), synovial polymorphonuclear cells percentage, and synovial α-defensin immunoassay value at the admission were retrieved from the electronic medical record.

RESULTS

The calculated optimal threshold for synovial ANC of 1,415.5 cells/μL was associated with an area under the receiver operating characteristic curve (AUC) of 0.930 for chronic knee PJI diagnosis. The calculated optimal threshold for synovial ANC of 2,247 cells/μL was associated with an AUC of 0.905 for chronic hip PJI diagnosis.

CONCLUSIONS

This study has conclusively shown that the synovial ANC serves as a valuable marker in the complicated diagnosis of PJI. This highly effective and efficient approach should be utilized for obtaining further information through standard tests, thereby ruling out the possibility of PJI.

LEVEL OF EVIDENCE

III.

What is the diagnostic accuracy of neutrophil to lymphocyte ratio and monocyte to lymphocyte ratio in detecting acute periprosthetic joint infections? A gender-specific analysis

PURPOSE

The accurate and timely diagnosis of periprosthetic joint infection (PJI) is critical for guiding optimal treatment management and success, highlighting the requirement of readily available inexpensive serum biomarkers to increase the diagnostic accuracy for PJI. Many studies have investigated the diagnostic accuracy of neutrophil to lymphocyte ratio (NLR) and monocyte to lymphocyte ratio (MLR). However, there is a lack of existing literature regarding optimal thresholds for acute PJI. The purpose of this study was to reveal the most appropriate cut-off values for MLR and NLR in detecting acute PJI with a gender specific analysis.

METHODS

Patients were classified as having an acute PJI if they met the International Consensus Meeting (ICM) 2018 modified criteria. Patients who had a negative clinical and diagnostic workup for a PJI and the presence of erythema on the index surgical area were included in the erysipelas group (control group). Data obtained from all patients included age, sex, body mass index (BMI), Charlson Comorbidity Index (CCI), procedure type (THA or TKA), serum C-reactive protein (CRP), and blood studies at the admission and culture results were retrieved from the electronic medical record.

RESULTS

ROC curve analysis was used to determine the gender-specific optimal threshold values for CRP, NLR, and MLR. Comparing the sensitivities and specificities of NLR and MLR at the identified best thresholds in males and females, the study found similar sensitivities of NLR in males and females with 0.84 and 0.84, respectively. On the other hand, an MLR of 0.67 or more reported a notably higher specificity in male patients [0.90 (95% CI 0.75-0.96) versus 0.70 (95% CI 0.56-0.80)].

CONCLUSION

NLR and MLR represent commonly ordered, low-cost, simple, and readily available complete cell count laboratory values and should be used as adjunct tests with reasonable diagnostic accuracy in detecting acute PJIs. Moreover, with its excellent specificity and PPV, MLR could provide valuable insight in diagnosing acute PJI, particularly in male patients.

LEVEL OF EVIDENCE

Level III Retrospective Cohort analysis.

Which Combination is Best? A Comparison of the Predictive Potential of Serum Biomarker Combinations to Diagnose Periprosthetic Joint Infection

BACKGROUND

Without a gold standard test, recent periprosthetic joint infections (PJI) literature has explored the utility of combining serological results, with promising findings. However, previous studies evaluated fewer than 200 patients and often studied only 1 to 2 test combinations. The purpose of this study was to accumulate a large single institution cohort of revision total joint arthroplasty (rTJA) patients to determine the diagnostic utility of combination serum biomarkers to identify PJI.

METHODS

A single institution longitudinal database was assessed to identify all patients who underwent rTJA from 2017 to 2020. There were 1,363 rTJA patients (715 rTKA patients and 648 rTHA patients) including 273 PJI cases (20%) analyzed. The PJI was diagnosed post-rTJA utilizing 2011 Musculoskeletal Infection Society (MSIS) criteria. Erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), D-dimer, and interleukin 6 (IL-6) were systematically collected for all patients.

RESULTS

The rTKA combination markers of CRP+ESR (sensitivity: 78.3%, specificity: 88.8%, positive predictive value (PPV): 70.0%, negative predictive value (NPV): 92.5%), CRP+D-dimer (sensitivity: 60.5%, specificity: 92.6%, PPV: 63.4%, NPV: 91.7%), and CRP+IL-6 (sensitivity: 38.5%, specificity: 100.0%, PPV: 100.0%, NPV: 92.9%) all yielded higher specificity than CRP alone (sensitivity: 94.4%, specificity: 75.0%, PPV: 55.5%, NPV: 97.6%). Similarly, the rTHA combination markers of CRP+ESR (sensitivity: 70.1%, specificity: 88.8%, PPV: 58.1%, NPV: 93.1%), CRP+D-dimer (sensitivity: 57.1%, specificity: 90.1%, PPV: 43.2%, NPV: 94.1%), and CRP+IL-6 (sensitivity: 21.4%, specificity: 98.4%, PPV: 60.0%, NPV: 91.7%) all yielded higher specificity than CRP alone (sensitivity: 84.7%, specificity: 77.5%, PPV: 45.4%, NPV: 95.8%).

CONCLUSIONS

Overall, in diagnosing PJI for both rTKA and rTHA, two marker combinations yielded higher specificity, while three marker combinations yielded higher sensitivity compared to CRP alone. However, compared to all two and three marker combinations, CRP demonstrated superior overall diagnostic utility. These findings suggest that routine combination testing of markers for PJI diagnosis may be excessive and an unnecessary use of resources, especially in resource-limited situations.