The value of white blood cell counts before revision total knee arthroplasty

Differential synovial fluid white blood cell count for the diagnosis of chronic peri-prosthetic joint infection - a systematic review and meta-analysis

Introduction: Peri-prosthetic joint infection (PJI) is a significant complication of arthroplasty, lacking a single gold standard diagnostic test. Synovial fluid white blood cell (WBC) count and polymorphonuclear neutrophil (PMN) proportion are widely used diagnostic tools, but their optimal cutoffs remain unclear, particularly for chronic PJI. Material and methods: This systematic review and meta-analysis included 74 studies published between 2000 and 2024. Data on diagnostic performance (sensitivity, specificity, and diagnostic odds ratios - DORs) of WBC count and PMN proportions were analysed. Sub-group analyses and heterogeneity assessments were performed, and optimal cutoffs for diagnostic accuracy were identified. Results: The meta-analysis revealed a WBC count summary DOR of 58.38 (95 % CI - confidence interval: 48.48-70.32) with an area under the curve (AUC) of the summarized receiver operating characteristic curve of 0.952. The PMN proportion showed a DOR of 43.17 (95 % CI: 35.31-52.79) and an AUC of 0.941. Optimal diagnostic thresholds for chronic PJI were WBC count > 2600 cells per microlitre and PMN > 70 %. Rule-in thresholds (specificity > 95 %) were WBC count ≥ 3000 cells per microlitre and PMN ≥ 75 %, while rule-out thresholds (sensitivity > 95 %) were WBC count ≤ 1500 cells per microlitre and PMN ≤ 65 %. Confounding conditions such as fractures, inflammatory arthritis, and metal-related reactions reduced test accuracy. Conclusions: Synovial fluid analysis remains a critical diagnostic tool for chronic PJI. Thresholds of WBC count < 1500 and > 3000  cells per microlitre and PMN < 65 % and > 75 % provide reliable negative and positive predictive values. A standardized diagnostic framework is essential for addressing remaining controversies and ensuring consistent interpretation across clinical settings.

What Is the Diagnostic Performance and Accuracy of Serum Inflammatory Biomarkers and Synovial Fluid Analysis in Megaprosthetic Periprosthetic Joint Infections?

BACKGROUND

Serum biomarkers and synovial fluid analysis are valuable tools for the preoperative diagnosis of periprosthetic joint infections (PJIs). However, the literature on their utility in megaprostheses is limited. Our study aimed to assess the diagnostic performance and accuracy of four laboratory tests for diagnosing PJI in patients who have megaprostheses.

METHODS

We retrospectively reviewed 104 patients who underwent 126 revisions after oncologic megaprosthesis reconstruction. Revisions were stratified into aseptic and septic according to the International Consensus Meeting criteria. The PJIs were classified into acute and chronic infections based on time since index surgery. There were four tests assessed: serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), synovial white blood cell (WBC) count, and polymorphonuclear percentage (PMN%). Receiver operating characteristic curve analysis was conducted to assess their performance.

RESULTS

The diagnostic performance of preoperative tests in acute PJIs ranked by area under the curve was CRP (0.86), ESR (0.81), synovial WBC count (0.76), and synovial PMN% (0.69). In chronic PJIs, diagnostic performance ranked by area under the curve was synovial WBC count (0.80), CRP (0.77), ESR (0.71), and synovial PMN% (0.67). New cutoff values for diagnosing acute PJIs were identified as CRP ≥ 42 mg/L, synovial WBC count ≥ 5,500 cells/μL, and synovial PMN% ≥ 92.5%. For chronic PJIs, new cutoff values of CRP ≥ 31 mg/L, ESR ≥ 24.5 mm/hour, synovial WBC count ≥ 5,550 cells/μL, and synovial PMN% ≥ 76.5% were established. These cutoff values improved diagnostic accuracy in both acute and chronic PJIs.

CONCLUSIONS

Good to excellent diagnostic performance was seen with all tests except synovial PMN%. Adjusting cutoff values in patients who have megaprosthesis revisions improved diagnostic performance.

ACR Appropriateness Criteria® Imaging After Total Knee Arthroplasty: 2023 Update

Total knee arthroplasty is the most commonly performed joint replacement procedure in the United States. This manuscript will discuss the recommended imaging modalities for six clinical variants; 1. follow-up of symptomatic or asymptomatic patients with a total knee arthroplasty. Initial imaging, 2. Suspected infection after total knee arthroplasty. Additional imaging following radiographs, 3. Pain after total knee arthroplasty. Infection excluded. Suspect aseptic loosening or osteolysis or instability. Additional imaging following radiographs, 4. Pain after total knee arthroplasty. Suspect periprosthetic or hardware fracture. Additional imaging following radiographs, 5. Pain after total knee arthroplasty. Measuring component rotation. Additional imaging following radiographs, and 6. Pain after total knee arthroplasty. Suspect periprosthetic soft-tissue abnormality unrelated to infection, including quadriceps or patellar tendinopathy. Additional imaging following radiographs. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

2022 American Association of Hip and Knee Surgeons Symposium: Periprosthetic Joint Infection

Periprosthetic joint infection (PJI) is the leading cause of failure in patients undergoing total joint arthroplasty. This article is a brief summary of a symposium on PJI that was presented at the annual AAHKS meeting. It will provide an overview of current technqiues in the prevention, diagnosis, and management of PJI. It will also highlight emerging technologies in this setting.

Profiling the Immune Response to Periprosthetic Joint Infection and Non-Infectious Arthroplasty Failure

Arthroplasty failure is a major complication of joint replacement surgery. It can be caused by periprosthetic joint infection (PJI) or non-infectious etiologies, and often requires surgical intervention and (in select scenarios) resection and reimplantation of implanted devices. Fast and accurate diagnosis of PJI and non-infectious arthroplasty failure (NIAF) is critical to direct medical and surgical treatment; differentiation of PJI from NIAF may, however, be unclear in some cases. Traditional culture, nucleic acid amplification tests, metagenomic, and metatranscriptomic techniques for microbial detection have had success in differentiating the two entities, although microbiologically negative apparent PJI remains a challenge. Single host biomarkers or, alternatively, more advanced immune response profiling-based approaches may be applied to differentiate PJI from NIAF, overcoming limitations of microbial-based detection methods and possibly, especially with newer approaches, augmenting them. In this review, current approaches to arthroplasty failure diagnosis are briefly overviewed, followed by a review of host-based approaches for differentiation of PJI from NIAF, including exciting futuristic combinational multi-omics methodologies that may both detect pathogens and assess biological responses, illuminating causes of arthroplasty failure.

Reliable Diagnostic Tests and Thresholds for Preoperative Diagnosis of Non-Inflammatory Arthritis Periprosthetic Joint Infection: A Meta-analysis and Systematic Review

Objective

The current diagnostic criteria for periprosthetic joint infection (PJI) are diverse and controversial, leading to delayed diagnosis. This study aimed to evaluate and unify their diagnostic accuracy and the threshold selection of serum and synovial routine tests for PJI at an early stage.

Methods

We searched the MEDLINE and Embase databases for retrospective or prospective studies which reported preoperative‐available assays (serum, synovial, or culture tests) for the diagnosis of chronic PJI among inflammatory arthritis (IA) or non‐IA populations from January 1, 2000 to June 30, 2022. Threshold effective analysis was performed on synovial polymorphonuclear neutrophils (PMN%), synovial white blood cell (WBC), serum C‐reactive protein (CRP), and erythrocyte sedimentation rate (ESR) to find the relevant cut‐offs.

Results

Two hundred and sixteen studies and information from 45,316 individuals were included in the final analysis. Synovial laboratory‐based α‐defensin and calprotectin had the best comprehensive sensitivity (0.91 [0.86–0.94], 0.95 [0.88–0.98]) and specificity (0.96 [0.94‐0.97], 0.95 [0.89–0.98]) values. According to the threshold effect analysis, the recommended cut‐offs are 70% (sensitivity 0.89 [0.85–0.92], specificity 0.90 [0.87–0.93]), 4100/μL (sensitivity 0.90 [0.87–0.93], specificity 0.97 [0.93–0.98]), 13.5 mg/L (sensitivity 0.84 [0.78–0.89], specificity 0.83 [0.73–0.89]), and 30 mm/h (sensitivity 0.79 [0.74–0.83], specificity 0.78 [0.72–0.83]) for synovial PMN%, synovial WBC, serum CRP, and ESR, respectively, and tests seem to be more reliable among non‐IA patients.

Conclusions

The laboratory‐based synovial α‐defensin and synovial calprotectin are the two best independent preoperative diagnostic tests for PJI. A cut off of 70% for synovial PMN% and tighter cut‐offs for synovial WBC and serum CRP could have a better diagnostic accuracy for non‐IA patients with chronic PJI.

Periprosthetic ankle infection: eradication rate, complications, and limb salvage. A systematic review

BACKGROUND

This systematic review investigated the outcomes of revision surgery after periprosthetic ankle infection (PAI).

METHODS

According to the PRISMA statement, 9 studies with 131 PAIs surgically treated and analyzed were included. Demographics and surgical techniques with eradication rates and complications were reported.

RESULTS

Methicillin-sensitive Staphylococcus aureus (MSSA) (30.4%) and coagulase-negative Staphylococcus (CNS) (26.5%) were the most common microorganisms. The eradication rate was 91.7% with permanent antibiotic spacers (SPC), 84.4% with 2-stage, 79.4% with arthrodesis (AA), and 58.8% with debridement and implant retention (DAIR). DAIR showed a significantly lower eradication rate than 2-stage (p = 0.016) and SPC (p = 0.043). Amputations occurred in 25% of patients after SPC, 8.8% after AA and 3.9% after DAIR. SPC showed a significantly higher amputation rate than DAIR and 2-stage (p = 0.044, and p = 0.017, respectively).

CONCLUSIONS

SPC and 2-stage revision show the highest eradication rates, but 2-stage has a lower risk of amputation.

Variation of synovial fluid leucocyte cell count and polymorphonuclear percentage in patients with aseptic revision total knee arthroplasty

AIMS

Current guidelines consider analyses of joint aspirates, including leucocyte cell count (LC) and polymorphonuclear percentage (PMN%) as a diagnostic mainstay of periprosthetic joint infection (PJI). It is unclear if these parameters are subject to a certain degree of variability over time. Therefore, the aim of this study was to evaluate the variation of LC and PMN% in patients with aseptic revision total knee arthroplasty (TKA).

METHODS

We conducted a prospective, double-centre study of 40 patients with 40 knee joints. Patients underwent joint aspiration at two different time points with a maximum period of 120 days in between these interventions and without any events such as other joint aspirations or surgeries. The main indications for TKA revision surgery were aseptic implant loosening (n = 24) and joint instability (n = 11).

RESULTS

Overall, 80 synovial fluid samples of 40 patients were analyzed. The average time period between the joint aspirations was 50 days (SD 32). There was a significantly higher percentage change in LC when compared to PMN% (44.1% (SD 28.6%) vs 27.3% (SD 23.7%); p = 0.003). When applying standard definition criteria, LC counts were found to skip back and forth between the two time points with exceeding the thresholds in up to 20% of cases, which was significantly more compared to PMN% for the European Bone and Joint Infection Society (EBJIS) criteria (p = 0.001), as well as for Musculoskeletal Infection Society (MSIS) (p = 0.029).

CONCLUSION

LC and PMN% are subject to considerable variation. According to its higher interindividual variance, LC evaluation might contribute to false-positive or false-negative results in PJI assessment. Single LC testing prior to TKA revision surgery seems to be insufficient to exclude PJI. On the basis of the obtained results, PMN% analyses overrule LC measurements with regard to a conclusive diagnostic algorithm. Cite this article: Bone Jt Open 2021;2(8):566-572.

Next generation sequencing for pathogen detection in periprosthetic joint infections

Periprosthetic joint infections (PJI) represent one of the most catastrophic complications following total joint arthroplasty (TJA). The lack of standardized diagnostic tests and protocols for PJI is a challenge for arthroplasty surgeons.Next generation sequencing (NGS) is an innovative diagnostic tool that can sequence microbial deoxyribonucleic acids (DNA) from a synovial fluid sample: all DNA present in a specimen is sequenced in parallel, generating millions of reads. It has been shown to be extremely useful in a culture-negative PJI setting.Metagenomic NGS (mNGS) allows for universal pathogen detection, regardless of microbe type, in a 24-48-hour timeframe: in its nanopore-base variation, mNGS also allows for antimicrobial resistance characterization.Cell-free DNA (cfDNA) NGS, characterized by lack of the cell lysis step, has a fast run-time (hours) and, together with a high sensitivity and specificity in microorganism isolation, may provide information on the presence of antimicrobial resistance genes.Metagenomics and cfDNA testing have reduced the time needed to detect infecting bacteria and represent very promising technologies for fast PJI diagnosis.NGS technologies are revolutionary methods that could disrupt the diagnostic paradigm of PJI, but a comprehensive collection of clinical evidence is still needed before they become widely used diagnostic tools. Cite this article: EFORT Open Rev 2021;6:236-244. DOI: 10.1302/2058-5241.6.200099.

The Graphical Representation of Cell Count Representation: A New Procedure for the Diagnosis of Periprosthetic Joint Infections

Aim: This study was designed to answer the question whether a graphical representation increase the diagnostic value of automated leucocyte counting of the synovial fluid in the diagnosis of periprosthetic joint infections (PJI). Material and methods: Synovial aspirates from 322 patients (162 women, 160 men) with revisions of 192 total knee and 130 hip arthroplasties were analysed with microbiological cultivation, determination of cell counts and assay of the biomarker alpha-defensin (170 cases). In addition, microbiological and histological analysis of the periprosthetic tissue obtained during the revision surgery was carried out using the ICM classification and the histological classification of Morawietz and Krenn. The synovial aspirates were additionally analysed to produce dot plot representations (LMNE matrices) of the cells and particles in the aspirates using the hematology analyser ABX Pentra XL 80. Results: 112 patients (34.8%) had an infection according to the ICM criteria. When analysing the graphical LMNE matrices from synovia cell counting, four types could be differentiated: the type “wear particles” (I) in 28.3%, the type “infection” (II) in 24.8%, the “combined” type (III) in 15.5% and “indeterminate” type (IV) in 31.4%. There was a significant correlation between the graphical LMNE-types and the histological types of Morawietz and Krenn (p < 0.001 and Cramer test V value of 0.529). The addition of the LMNE-Matrix assessment increased the diagnostic value of the cell count and the cut-off value of the WBC count could be set lower by adding the LMNE-Matrix to the diagnostic procedure. Conclusion: The graphical representation of the cell count analysis of synovial aspirates is a new and helpful method for differentiating between real periprosthetic infections with an increased leukocyte count and false positive data resulting from wear particles. This new approach helps to increase the diagnostic value of cell count analysis in the diagnosis of PJI.

False-Positive Automated Synovial Fluid White Blood Cell Counting Is a Concern for Both Hip and Knee Arthroplasty Aspirates

BACKGROUND

Although false elevation of automated leukocyte (white blood cell [WBC]) counts has been described in the setting of hip corrosion, the more general correlation between manual and automated cell counts among synovial fluid aspirates from hip and knee arthroplasties has not been studied.

METHODS

This retrospective review at one laboratory identified 8607 consecutive synovial fluid samples from arthroplasties and 812 from native knees, each with an automated WBC count > 3000 cells/μL and a corresponding paired reflex manual count. The correlation between automated and manual counts was evaluated, as was the rate of false-positive automated WBC counts.

RESULTS

The correlation between automated WBC counts for native knees, total knee arthroplasties, and total hip arthroplasties was near-perfect, strong, and moderate, respectively. The false-positive rates for automated counts were 4.4%, 10.1%, and 34.3%, respectively (P < .0001). International Consensus Meeting scores and culture positivity demonstrated that manual counts, not automated counts, were correct.

CONCLUSION

The presence of a hip or knee arthroplasty appears to substantially increase the risk of a false-positive automated synovial fluid WBC count. Clinicians evaluating an arthroplasty should exercise caution when interpreting positive automated WBC counts, and consider requesting a reflex manual count, to verify the accuracy of automated cell counting.

The Quality of Diagnostic Studies in Periprosthetic Joint Infections: Can We Do Better?

BACKGROUND

The diagnosis of periprosthetic joint infections (PJIs) continues to be a subject of extensive debate. This is in part due to the lack of a single "gold standard" test, and the marked heterogeneity in the design of studies evaluating the accuracy of different diagnostic modalities. The goal of this review is to critically analyze the evidence cited by the proceedings of the 2013 International Consensus Meeting (ICM) on PJI with regards to the diagnosis of PJI.

METHODS

References from the Proceedings of the ICM on PJI related to PJI minor criteria were retrieved and manually reviewed. A total of 25 studies were analyzed using a Validated Quality Assessment of Diagnostic Accuracy Studies tool.

RESULTS

A large number of studies were determined to have a high risk of bias for flow and timing domains due to the large numbers of exclusions. Studies of synovial white blood cells count and polymorphonuclear neutrophils percentage suffered from threshold optimization and lack of internal validity. Furthermore, due to the lack of homogeneity across studies, index test and reference standard domains showed high risk of bias for white blood cell/polymorphonuclear neutrophil percentage and the utility histological analysis, respectively. Leukocyte esterase testing lacked standardization with regard to the strip reagent used, and the exclusion of bloody samples limited sample sizes.

CONCLUSION

The 2013 ICM minor criteria were based on studies with a low quality of evidence. As the committee continues to adjust these guidelines, they should encourage future studies with sound clinical design, patient selection, and testing procedures.

Factors to Consider When Assessing the Diagnostic Accuracy of Synovial Leukocyte Count in Periprosthetic Joint Infection

Synovial white blood cell (WBC) count and the percentage of polymorphonuclear leucocytes (PMN%) is one of the diagnostic criteria to diagnose a periprosthetic joint infection (PJI). Although the test is widely available, the diagnostic accuracy of proposed cut-off levels are influenced by several factors, such as: the affected joint, co-morbid conditions, the causative microorganism and the gathering and processing of samples in the laboratory. In this narrative review we provide an overview on how and to what extent these factors can affect the synovial WBC count and PMN% in synovial fluid.

What Strategies Can Be Implemented to Help Isolate the Causative Organism in Patients With Infection of the Foot and Ankle?

RECOMMENDATION

Transfer of synovial aspirate in blood culture bottles, obtaining deep biopsy of tissues and bone, obtaining multiple samples, increasing incubation period of cultures, and the use of molecular techniques for culture negative cases are some of the strategies that can help improve the ability to isolate the causative organism(s) in infections of foot and ankle.

LEVEL OF EVIDENCE

Moderate.

DELEGATE VOTE

Agree: 100%, Disagree: 0%, Abstain: 0% (Unanimous, Strongest Consensus).

Proceedings from the 2018 International Consensus Meeting on Orthopedic Infections: evaluation of periprosthetic shoulder infection

The Second International Consensus Meeting on Orthopedic Infections was held in Philadelphia, Pennsylvania, in July 2018. More than 800 experts from all 9 subspecialties of orthopedic surgery and allied fields of infectious disease, microbiology, and epidemiology were assembled to form the International Consensus Group. The shoulder workgroup reached consensus on 27 questions related to culture techniques, inflammatory markers, and diagnostic criteria used to evaluate patients for periprosthetic shoulder infection. This document contains the group's recommendations and rationale for each question related to evaluating periprosthetic shoulder infection.

Diagnostic Accuracy of Serum, Synovial, and Tissue Testing for Chronic Periprosthetic Joint Infection After Hip and Knee Replacements: A Systematic Review

BACKGROUND

Chronic periprosthetic joint infection (PJI) is a devastating complication that can occur following total joint replacement. Patients with chronic PJI report a substantially lower quality of life and face a higher risk of short-term mortality. Establishing a diagnosis of chronic PJI is challenging because of conflicting guidelines, numerous tests, and limited evidence. Delays in diagnosing PJI are associated with poorer outcomes and morbid revision surgery. The purpose of this systematic review was to compare the diagnostic accuracy of serum, synovial, and tissue-based tests for chronic PJI.

METHODS

This review adheres to the Cochrane Collaboration's diagnostic test accuracy methods for evidence searching and syntheses. A detailed search of MEDLINE, Embase, the Cochrane Library, and the grey literature was performed to identify studies involving the diagnosis of chronic PJI in patients with hip or knee replacement. Eligible studies were assessed for quality and bias using the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) tool. Meta-analyses were performed on tests with sufficient data points. Summary estimates and hierarchical summary receiver operating characteristic (HSROC) curves were obtained using a bivariate model.

RESULTS

A total of 12,616 citations were identified, and 203 studies met the inclusion criteria. Of these 203 studies, 170 had a high risk of bias. Eighty-three unique PJI diagnostic tests were identified, and 17 underwent meta-analyses. Laboratory-based synovial alpha-defensin tests and leukocyte esterase reagent (LER) strips (2+) had the best performance, followed by white blood-cell (WBC) count, measurement of synovial C-reactive protein (CRP) level, measurement of the polymorphonuclear neutrophil percentage (PMN%), and the alpha-defensin lateral flow test kit (Youden index ranging from 0.78 to 0.94). Tissue-based tests and 3 serum tests (measurement of interleukin-6 [IL-6] level, CRP level, and erythrocyte sedimentation rate [ESR]) had a Youden index between 0.61 to 0.75 but exhibited poorer performance compared with the synovial tests mentioned above.

CONCLUSIONS

The quality of the literature pertaining to chronic PJI diagnostic tests is heterogeneous, and the studies are at a high risk for bias. We believe that greater transparency and more complete reporting in studies of diagnostic test results should be mandated by peer-reviewed journals. The available literature suggests that several synovial fluid-based tests perform well for diagnosing chronic PJI and their use is recommended in the work-up of any suspected case of chronic PJI.

LEVEL OF EVIDENCE

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Consensus document for the diagnosis of prosthetic joint infections: a joint paper by the EANM, EBJIS, and ESR (with ESCMID endorsement)

Background

For the diagnosis of prosthetic joint infection, real evidence-based guidelines to aid clinicians in choosing the most accurate diagnostic strategy are lacking.

Aim and Methods

To address this need, we performed a multidisciplinary systematic review of relevant nuclear medicine, radiological, orthopaedic, infectious, and microbiological literature to define the diagnostic accuracy of each diagnostic technique and to address and provide evidence-based answers on uniform statements for each topic that was found to be important to develop a commonly agreed upon diagnostic flowchart.

Results and Conclusion

The approach used to prepare this set of multidisciplinary guidelines was to define statements of interest and follow the procedure indicated by the Oxford Centre for Evidence-based Medicine (OCEBM).

Electronic supplementary material

The online version of this article (10.1007/s00259-019-4263-9) contains supplementary material, which is available to authorized users.

Diagnosing Periprosthetic Joint Infection in Inflammatory Arthritis: Assumption Is the Enemy of True Understanding

BACKGROUND

Despite concern over the interpretation of serum and synovial fluid tests to screen and diagnose periprosthetic joint infection (PJI) in patients with inflammatory arthritis, only a single study has investigated this area. We aimed to assess accuracy of clinical and laboratory markers for PJI diagnosis in the context of underlying inflammatory arthritis.

METHODS

This multicenter study was conducted on total joint arthroplasty patients at 3 different centers between 2001 and 2016. PJI was defined based on Musculoskeletal Infection Society criteria. Acute PJI cases were excluded. Patients operated for a diagnosis other than infection, who did not subsequently fail at 1-year follow-up, were considered aseptic revisions. Serum C-reactive protein and erythrocyte sedimentation rate, synovial white blood cell and differential, as well as alpha-defensin and results of frozen section were documented.

RESULTS

In total, 1220 patients undergoing revision total joint arthroplasty (567 PJI, 653 aseptic) were included. Fifty-five septic patients and 61 in the aseptic group had inflammatory arthritis. Although mean levels of serum C-reactive protein and synovial white blood cell in inflammatory arthritis patients were significantly higher compared to patients without inflammatory arthritis, there were no significant differences in PJI patients. The thresholds associated with increased risk for PJI in patients with and without inflammatory arthritis were similar and closely resembled traditional cut-points.

CONCLUSION

We demonstrate higher baseline immune upregulation in aseptic revision cases with inflammatory arthritis, but no significant differences are seen for PJI. Conventional PJI thresholds for serum and synovial diagnostic markers should be adhered to. Assumptions about inflammatory arthritis patients needing differential diagnostic protocols should be avoided.

Usefulness of Culturing the Periprosthetic Membrane or Neosynovium for the Diagnosis of Infection During Hip and Knee Revision Arthroplasty

INTRODUCTION

Identification of microorganisms is critical for correct management of an infected arthroplasty. Our hypothesis is that the culture yield depends on the location around the prosthesis from which samples are obtained.

METHODS

This prospective study included 298 revisions of the hip (123) and knee (175). We compared the yield of the intraoperative samples obtained, which included synovial fluid (two), neosynovium (two), and periprosthetic membrane (two).

RESULTS

Cultures were positive in 28 cases, in which 15 had the same diagnosis considering either the neosynovium or the membrane, and there were 3 cases in which the infection could have been diagnosed only by considering the combination of both. In all, there were 8 cases in which the infection might have been misdiagnosed unless considering a combination of both solid tissue samples (P = 0.004).

CONCLUSIONS

The yields of the periprosthetic membrane and neosynovium do not differ significantly, and we recommend considering a combination of both.

LEVEL OF EVIDENCE

Diagnostic Level II.

How Reliable Is the Cell Count Analysis in the Diagnosis of Prosthetic Joint Infection?

BACKGROUND

Synovial analysis of joint aspirates is a key diagnostic tool; all major diagnostic algorithms include cell count (CC) and polymorphonuclear percentage (PMN%) as important criteria to make the diagnosis. In this context, we conducted this study to analyze the overall accuracy of CC and PMN%.

METHODS

A single-center retrospective analysis was performed with clinical data of included patients, with a total of 524 preoperative joint aspirations (255 hips, 269 knees). From the aspirated synovial fluid, we tested the leukocyte esterase activity, leukocyte CC, and PMN%, and sent specimens for aerobic and anaerobic bacterial culture. Depending on the clinical results in accordance with the Musculoskeletal Infection Society criteria for prosthetic joint infection (PJI), 203 patients were then admitted for aseptic revision and 134 patients for septic exchange.

RESULTS

In 337 cases (64.3% of the study patients), it was possible to measure the CC. The best cutoff level for PJI of all study patients was 2582 leukocytes/μL (sensitivity [SE] 80.6%, specificity [SP] 85.2%) and a PMN% of 66.1% (SE 80.6%, SP 83.3%). The chosen cutoff levels for PJI of total knee and total hip arthroplasty were 1630 leukocytes/μL (SE 83.6%, SP 82.2%) and a PMN% of 60.5% (SE 80.3%, SP 77.1%) and 3063 leukocytes/μL (SE 78.1%, SP 80.0%) and a PMN% of 66.1% (SE 82.2%, SP 82.4%), respectively.

CONCLUSIONS

CC and PMN% are sensitive methods for diagnosing PJI of total hip and total knee arthroplasty. However, there are differences in cutoff levels between knees and hips. International guidelines and diagnostic criteria need revisions in terms of these parameters.

Evidence-Based Management of Trunnionosis in Metal-on-Polyethylene Total Hip Arthroplasty: A Systematic Review

Multiple recent reports have indicated a rising awareness of trunnionosis-related implant failures, accounting for up to 3% of all total hip arthroplasty revisions. Moreover, aseptic loosening and osteolysis from local release of metal debris can be the presenting manifestations, and thus the true incidence of trunnionosis is thought to be underreported. Furthermore, the relatively unclear and multifactorial pathogenesis and the widely variable clinical presentations pose a diagnostic challenge. A consensus regarding the ideal intervention and its timing is also lacking. Because of the relative paucity of reports regarding the diagnosis and management of trunnionosis, we conducted this evidence-based review to evaluate the (1) incidence, (2) pathogenesis, (3) diagnosis, and (4) treatment of trunnionosis in metal-on-polyethylene total hip arthroplasty. We then propose an algorithm for the diagnostic work-up and management of this condition.

Two-Stage Revision Arthroplasty for the Treatment of Prosthetic Joint Infection

PURPOSE OF REVIEW

To review the diagnosis and treatment of prosthetic joint infection (PJI) with a focus on two-stage revision arthroplasty. The text will discuss different spacer constructs in total knee and total hip arthroplasty and will present clinical outcome data for these various options.

RECENT FINDINGS

There is no appreciable difference in infection eradication between mobile and static antibiotic spacers. Mobile spacers have shown improved knee range of motion after second-stage re-implantation. Two-stage revision arthroplasty is the gold standard treatment for PJI. The first stage involves removal of all components, cement, and compromised soft tissues with placement of an antibiotic-impregnated spacer. Spacer options include both mobile and static spacers. Mobile spacers offer maintenance of ambulation and joint range of motion between staged procedures and have shown to be as effective in eradicating infection as static spacers.

Current Recommendations for the Diagnosis of Acute and Chronic PJI for Hip and Knee-Cell Counts, Alpha-Defensin, Leukocyte Esterase, Next-generation Sequencing

PURPOSE OF REVIEW

Despite significant progress in recent years, the diagnosis of periprosthetic joint infection (PJI) remains a challenge and no gold standard test exists. A combination of serological, synovial, microbiological, histological, and radiological investigations is performed that are expensive, often invasive, and imperfect. Novel biomarkers and molecular methods have shown promise in recent years. The purpose of this review is to provide an update about the diagnostic recommendations for PJI and cover a selection of emerging diagnostic tools.

RECENT FINDINGS

Recent literature highlights a new evidence-based definition for diagnosing hip and knee PJI that shows excellent performance on formal external multi-institutional validation. There is also increasing evidence to support the measurement of selected biomarkers in serum and synovial fluid, such as alpha-defensin, D-dimer, and interleukin-6. Finally, the emerging utility of next-generation sequencing for pathogen identification is discussed. In summary, we describe current recommendations and emerging tests for the diagnosis of PJI. Residual limitations and directions for future research are also discussed.

Diagnostic parameters in periprosthetic infections: the current state of the literature

Despite progress in recent years, a definitive diagnosis of PPI is not yet possible. Due to new diagnostic possibilities and the further development of already existing diagnostic tools, a more accurate diagnostic clarification of uncertain cases should be possible. The following article includes an overview of common existing diagnostic tools and instruments, which will likely gain importance in the future.

Different Kinetics of Perioperative CRP after Hip Arthroplasty for Elderly Femoral Neck Fracture with Elevated Preoperative CRP

This study aimed to determine the kinetics of four inflammatory markers and to identify the variables that affect the natural kinetics of inflammatory markers in aged patients having hip fractures with and without elevated preoperative CRP. 240 elderly patients who have been operated on for femoral neck fracture with no infectious complications were divided into two groups on elevated preoperative CRP level (>10 mg/L). The temporal values of four inflammatory markers of WBC, neutrophil count (N) (%), ESR, and CRP were assessed eight times every other day until the 14th postoperative day. At 48–60 h postoperatively, mean CRP was markedly higher in patients with preoperatively elevated CRP than in those with nonelevated CRP (122.1 ± 65.9 and 73.7 ± 35.5, p < 0.001). However, the abrupt elevation of CRP in the elevated group was conversely decreased on the 4th-5th postoperative day, demonstrating similar kinetic curves with no significant differences between both groups. For WBC, N (%), and ESR, both groups showed similar patterns of temporal values 14 days after surgery regardless of preoperative CRP level. Our findings could be used as guidelines for patient discharge and during the follow-up period after surgery.

ACR Appropriateness Criteria® Imaging After Total Knee Arthroplasty

Total knee arthroplasty (TKA) is the most commonly performed joint replacement procedure in the United States and annual demand for primary TKA is expected to grow by 673% by 2030. The first part provides an overview of imaging modalities (radiographs, CT, MRI, ultrasound, and various nuclear medicine studies) and discusses their usefulness in the imaging evaluation of TKA. The second part focuses on evidence-based imaging and imaging-guided intervention algorithms for the workup of TKA and its complications, including routine follow-up, component wear, periprosthetic infection, aseptic loosening, granulomas/osteolysis, conventional and rotational instability, periprosthetic fracture, patellar complications, and a variety of periprosthetic soft tissue abnormalities. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Rheumatoid Arthritis, Disease Modifying Agents, and Periprosthetic Joint Infection: What Does a Joint Surgeon Need to Know?

The incidence of periprosthetic joint infection (PJI) among patients with rheumatoid arthritis (RA) is 1.6× greater than in patients undergoing the same procedure for osteoarthritis. This higher risk "may" be due to the immunosuppressive therapies for RA patients including corticosteroids, such as prednisone, and disease-modifying antirheumatic drugs (DMARDs), such as methotrexate. There is a debate about the role of DMARDs in increasing the incidence of subsequent PJI. Studies show conflicting results, with some demonstrating no significant increase in the rates of PJI and some finding otherwise. The International Consensus Meeting on PJI recommended that DMARDs should be halted prior to an elective total joint arthroplasty based on their half-life. Moreover, the International Consensus Meeting stated that cessation of immunosuppressant medications should be performed in consultation with and under the direction of the treating physician. In this review, we aimed to provide an introduction to the available treatment options and cover the recommendations on the treatment protocols for RA patients who undergo elective total joint arthroplasty.

Synovial Fluid Biomarkers for the Diagnosis of Periprosthetic Joint Infection: A Systematic Review and Meta-Analysis

BACKGROUND

The search for a single standard reference test for determining periprosthetic joint infection (PJI) through analysis of synovial fluid has yielded numerous biomarkers as potential candidates. The purpose of the present systematic review and meta-analysis was to evaluate the diagnostic accuracy of synovial fluid biomarkers and to determine which test has the highest diagnostic odds ratio (DOR) for the diagnosis of PJI.

METHODS

An online literature search of the MEDLINE, Embase, and Cochrane databases identified 33 articles reporting a total of 13 major parameters for diagnosing PJI through analysis of synovial fluid. Each of the included articles was independently analyzed for risk of bias and for concerns regarding applicability utilizing the QUADAS-2 (Quality Assessment of Diagnostic Accuracy Studies-2) tool. The mada (meta-analysis of diagnostic accuracy) tool was used to generate forest plots for sensitivity, specificity, and the log of the DOR, as well as summary statistics.

RESULTS

In this analysis, 13 index tests (leukocyte count; measurement of the percentage of polymorphonucleocytes [PMN%] and the levels of C-reactive protein [CRP], α-defensin, leukocyte esterase [LE], interleukin [IL]-6, IL-8, IL-10, IL-1β, vascular endothelial growth factor [VEGF], and granulocyte-colony stimulating factor [G-CSF]; culture; and polymerase chain reaction [PCR] analysis) were evaluated on the basis of ≥2 articles. Of these tests, 8 (leukocyte count, PMN%, CRP, α-defensin, LE, IL-6, IL-8, and culture) were appropriate for pooled analysis. The overall sensitivity of these 8 markers was 0.85, and all but culture showed a sensitivity of ≥0.8. All markers showed a specificity of ≥0.9. Of the 8 tests, measurement of the α-defensin level showed the highest log DOR.

CONCLUSIONS

Synovial fluid leukocyte count, PMN%, CRP, α-defensin, LE, IL-6, and IL-8 all demonstrated high sensitivity for diagnosing PJI, with α-defensin being the best synovial marker based on the highest log DOR. However, other synovial fluid tests that demonstrate good diagnostic performance can also be used in combination for the diagnosis of PJI.

LEVEL OF EVIDENCE

Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Diagnostic Value of Synovial White Blood Cell Count and Serum C-Reactive Protein for Acute Periprosthetic Joint Infection After Knee Arthroplasty

BACKGROUND

The diagnosis of periprosthetic joint infection (PJI) remains difficult, particularly in acute postoperative stage. The purpose of this study was to investigate the optimal cutoff value of synovial white blood cell (WBC) count, percentage of polymorphonuclear cells, erythrocyte sedimentation rate, and C-reactive protein (CRP) for diagnosing early postoperative infection after knee joint arthroplasty.

METHODS

We retrospectively reviewed primary total knee arthroplasties and unicompartmental knee arthroplasties, with a knee aspiration within 3 weeks of surgery, from January 2006 to November 2016. Twelve infected cases and 185 uninfected cases met the inclusion criteria of our study. We compared the laboratory parameters (synovial WBC count, percentage of polymorphonuclear cells, erythrocyte sedimentation rate, and CRP levels) between the 2 groups. Receiver operating characteristic curves were constructed to determine the optimal cutoff values for each parameter. Each parameter was studied to determine its sensitivity, specificity, and positive and negative predictive values (PPV and NPV) in diagnosing acute PJI.

RESULTS

There were 2 optimal cutoff values for synovial WBC count and CRP levels. With the cutoff value of synovial WBC set at 11,200 cells/μL, acute PJI could be diagnosed with the highest sensitivity (100%) and specificity (98.9%); with the cutoff value set at 16,000 cells/μL, the best PPV and NPV were found (100% and 99.5%, respectively). Similarly, the CRP level >34.9 mg/L had the best sensitivity (100%) and specificity (90.3%), whereas the CRP level >74.5 mg/L had the best PPV (100%) and NPV (99.2%).

CONCLUSION

Synovial WBC count and CRP levels are useful in diagnosing acute PJI between 1 and 3 weeks after primary knee arthroplasty.

The analysis of synovial fluid in total knee arthroplasties with flexion instability

AIMS

Patients with flexion instability after total knee arthroplasty (TKA) often present with a recurrent effusion, which may be a haemarthrosis. While the radiographic factors contributing to flexion instability have been elucidated, the clinical diagnosis remains challenging. Our aim, in this study, was to determine the mean white cell count and differential profile in pre-operative aspirations of synovial fluid in a consecutive series of patients undergoing revision TKA for flexion instability.

PATIENTS AND METHODS

Between 2000 and 2010, 60 patients undergoing aseptic revision TKA for flexion instability were identified. The results of the pre-operative aspiration of synovial fluid were available for 53 patients (88%). These patients were 1:2 matched to 106 patients who underwent aseptic TKA for indications other than flexion instability. The mean age of the patients at revision TKA was 65 years (44 to 82) and 55% were women. The mean follow-up was 4.3 years (2 to 10.2).

RESULTS

In the flexion instability group, the median total cell count was 312 cells/µL (interquartile range (IQR) 104 to 624), with a mean distribution of 45% macrophages (2% to 90%), 30% lymphocytes (1% to 69%), 18% neutrophils (0% to 80%), 0.5% eosinophils (0% to 6%) and 7% other cells (0% to 42%; mainly synovial cells). There was no significant difference in the median total cell count (p = 0.14) or mean distribution of macrophages (p = 0.42), lymphocytes (p = 0.38), neutrophils (p = 0.19) and eosinophils (p = 0.89) between the flexion instability and control groups. There was a significant difference in the percentage of bloody serosanguineous aspirations which was 58% in the flexion instability group and 18% in the control group (odds ratio = 6.5; p = 0.0001).

CONCLUSIONS

In the group of patients who underwent revision TKA for flexion instability, most had a mean cell count and differential similar to those who underwent revision for other aseptic indications. However, bloody serosanguineous aspirations were 6.5 times more common in those with flexion instability confirming that many of the recurrent effusions seen in this condition are haemarthroses. Cite this article: Bone Joint J 2017;99-B:1477-81.

The Role of Biomarkers for the Diagnosis of Implant-Related Infections in Orthopaedics and Trauma

Diagnosis of implant-related (periprosthetic joint) infections poses a major challenge to infection disease physicians and orthopaedic surgeons. Conventional diagnostic tests continue to suffer from issues of accuracy and feasibility. Biomarkers are used throughout medicine for diagnostic and prognostic purposes, as they are able to objectively determine the presence of a disease or a biological state. There is increasing evidence to support the measurement of specific biomarkers in serum and/or synovial fluid of patients with suspected periprosthetic joint infections. Promising serum biomarkers include interleukin (IL)-4, IL-6, tumour necrosis factor (TNF)-α, procalcitonin, soluble intercellular adhesion molecule 1 (sICAM-1), and D-dimer. In addition to c-reactive protein and leucocyte esterase, promising biomarkers that can be measured in synovial fluid include antimicrobial proteins such as human β-defensin (HBD)-2 and human β-defensin (HBD)-3, and cathelicidin LL-37, as well as several interleukins such as IL-1β, IL-6, IL-8, IL-17, TNF- α, interferon-δ, and vascular endothelial growth factor.

How To Diagnose and Treat Infection in Total Ankle Arthroplasty

Periprosthetic infection after total ankle arthroplasty (TAA) is a serious complication, often requiring revision surgery, including revision arthroplasty, conversion to ankle arthrodesis, or even amputation. Risk factors for periprosthetic ankle infection include prior surgery at the site of infection, low functional preoperative score, diabetes, and wound healing problems. The clinical presentation of patients with periprosthetic ankle joint infection can be variable and dependent on infection manifestation: acute versus chronic. The initial evaluation in patients with suspected periprosthetic joint infections should include blood tests: C-reactive protein and erythrocyte sedimentation rate. Joint aspiration and synovial fluid analysis can help confirm suspected periprosthetic ankle infection.

Synovial Fluid Cell Count for Diagnosis of Chronic Periprosthetic Hip Infection

BACKGROUND

There is a paucity of data regarding the threshold of synovial fluid white blood-cell (WBC) count and polymorphonuclear cell (neutrophil) percentage of the WBC count (PMN%) for the diagnosis of chronic periprosthetic joint infection (PJI) after total hip arthroplasty. Despite this, many organizations have provided guidelines for the diagnosis of PJI that include synovial fluid WBC count and PMN%. We attempted to define a threshold for synovial fluid WBC count and PMN% for the diagnosis of chronic PJI of the hip using a uniform definition of PJI and to investigate any variations in the calculated thresholds among institutions.

METHODS

From 4 academic institutions, we formed a cohort of 453 patients with hip synovial fluid cell count analysis as part of the work-up for revision total hip arthroplasty. Using the definition of PJI from the Musculoskeletal Infection Society (MSIS), 374 joints were diagnosed as aseptic and 79, as septic. Intraoperative aspirations were performed as routine practice, regardless of the suspicion for infection, in 327 (72%) of the patients. Using receiver operating characteristic curves, the optimal threshold values for synovial WBC count and PMN% were identified.

RESULTS

For the diagnosis of chronic PJI of the hip, the threshold for the overall cohort was 3,966 cells/μL for WBC count and 80% for PMN%. Despite the high predictive accuracy for the cohort, there was notable institutional variation in fluid WBC count and PMN%. Furthermore, the rate of PJI was 14% (4 of 28) for patients with a WBC count of 3,000 to 5,000 cells/μL compared with 91% (20 of 22) for patients with a WBC count of >50,000 cells/μL. Similarly, the rate of PJI was 29% (14 of 49) for patients with a PMN% of 75% to 85% compared with 69% (33 of 48) for patients with a PMN% of >95%.

CONCLUSIONS

Using the MSIS criteria, the optimal synovial fluid WBC count and PMN% to diagnose chronic PJI in the hip is closer to thresholds for the knee than those previously reported for the hip. This study validates the diagnostic utility of synovial fluid analysis for the diagnosis of periprosthetic hip infection; however, we also identified a clinically important "gray area" around the threshold for which the presence of PJI may be unclear.

LEVEL OF EVIDENCE

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Synovial fluid white cell count and histopathological examination of periprosthetic tissue samples (frozen and permanent sections) in the diagnosis of prosthetic knee infection

The aim of the study was to determine prospectively the importance of synovial fluid white cell count and intraoperative frozen and permanent sections analysis (number of polymorphonuclear leukocytes per high-power field) in the diagnosis of septic total knee arthroplasty. There were studied prospectively 72 patients who needed a revision total knee arthroplasty between 2013-2015. 30 patients were diagnosed with prosthetic joint infection due to high rates of ESR (93%) and CRP (90%) and preoperative positive culture from aspirated synovial fluid and 42 patients were considered to have aseptic failure according to negative preoperative culture from joint aspirate. For all the patients was analysed synovial fluid white cell count and histopathological aspect of intraoperative frozen and permanent sections of periprosthetic tissue. The results showed a median value of 13800 of sinovial white cells count for infected knee and 92 for noninfected knee. 90% of the patients with joint infection had more than 5 polymorphonuclear leukocytes per high power field on intraoperative frozen sections and 83% on permanent sections. None of the patients from aseptic group had more than 5 polymorphonuclear leukocytes per field on permanent sections. The erythrocyte sedimentation rate and C-reactive protein level can be supplemented with cultures of aspirated joint fluid and fluid white cell count to confirm the diagnosis of periprosthetic infection. When the preoperative diagnosis remain unclear, the histological examination of frozen or permanent sections of periprosthetic tissue with at least 5 polymorphonuclear leukocytes per high power field, is predictive for the presence of infection.

"Combined Diagnostic Tool" APPlication to a Retrospective Series of Patients Undergoing Total Joint Revision Surgery

Background: Differentiating between septic and aseptic joint prosthesis may be challenging, since no single test is able to confirm or rule out infection. The choice and interpretation of the panel of tests performed in any case often relies on empirical evaluation and poorly validated scores. The "Combined Diagnostic Tool (CDT)" App, a smartphone application for iOS, was developed to allow to automatically calculate the probability of having a of periprosthetic joint infection, on the basis of the relative sensitivity and specificity of the positive and negative diagnostic tests performed in any given patient.

Objective: The aim of the present study was to apply the CDT software to investigate the ability of the tests routinely performed in three high-volume European centers to diagnose a periprosthetic infection.

Methods: This three-center retrospective study included 120 consecutive patients undergoing total hip or knee revision, and included 65 infected patients (Group A) and 55 patients without infection (Group B). The following parameters were evaluated: number and type of positive and negative diagnostic tests performed pre-, intra- and post-operatively and resultant probability calculated by the CDT App of having a peri-prosthetic joint infection, based on pre-, intra- and post-operative combined tests.

Results: Serological tests were the most common performed, with an average 2.7 tests per patient for Group A and 2.2 for Group B, followed by joint aspiration (0.9 and 0.8 tests per patient, respectively) and imaging techniques (0.5 and 0.2 test per patient). Mean CDT App calculated probability of having an infection based on pre-operative tests was 79.4% for patients in Group A and 35.7 in Group B. Twenty-nine patients in Group A had > 10% chance of not having an infection, and 29 of Group B had > 10% chance of having an infection.

Conclusion: This is the first retrospective study focused on investigating the number and type of tests commonly performed prior to joint revision surgery and aimed at evaluating their combined ability to diagnose a peri-prosthetic infection. CDT App allowed us to demonstrate that, on average, the routine combination of commonly used tests is unable to diagnose pre-operatively a peri-prosthetic infection with a probability higher than 90%.

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Zusammenfassung. Mit stetig steigender Häufigkeit endoprothetischer Eingriffe nimmt auch die Bedeutung der damit vergesellschafteten Revisionschirurgie zu. Die Gelenksprothesen-Infektion ist hierbei eine der schwerwiegendsten Komplikationen, die zur Erlangung eines bestmöglichen Behandlungsergebnisses eine differenzierte Diagnose- und Therapiestrategie erfordert. Anamnese, klinische Untersuchung, Laborkontrollen, Radiologie (konventionelle und spezialisierte), Gelenkspunktion sowie Mikrobiologie und Histologie liefern entscheidende Hinweise zur Diagnosestellung als unabdingbare Voraussetzung zur Erstellung und Einleitung des entsprechenden Therapiekonzeptes. Insbesondere die Abgrenzung zwischen aseptischen und septischen Prothesenlockerungen ist schwierig und erfordert ein differenziertes und interdisziplinäres Vorgehen. Die kurative Behandlungsstrategie ist abhängig von: Dauer der Symptome, Latenz seit Primärimplantation, Keimspektrum, Antibiogramm und Weichteilverhältnissen und umfasst prothesenerhaltende Strategien bei nicht gelockerter Prothese, reizlosen Weichteilen und Abwesenheit von Problemkeimen, bis hin zum kompletten ein- oder zweizeitigen Prothesenwechsel bei einer chronischen Infektion. In diesem Beitrag werden die aktuellen Management-Konzepte der Gelenksprothesen-Infektionen diskutiert.

Evaluating the Diagnostic Yield of Computed Tomography-Guided Aspirations in Suspected Post-operative Spine Infections

BACKGROUND

Early detection of surgical site infection (SSI) following spinal surgery would allow for prompt treatment and would improve overall outcome, yet early diagnosis is a challenge. Computed tomography (CT) guided aspiration of fluid collections may aid in diagnosis, as its diagnostic utility has previously been demonstrated in the setting of hip SSI, knee SSI, and spontaneous diskitis. There is no literature on its use in post-operative spinal SSIs.

QUESTIONS/PURPOSES

The current study aims to (1) determine the diagnostic value of CT-guided aspiration in evaluating suspected SSI; (2) identify the characteristics of the clinical presentation that are predictive of SSI; and (3) identify characteristics of the hematologic workup that are predictive of SSI.

METHODS

Thirty patients who underwent CT-guided aspiration of paraspinal post-operative fluid collections and culture of aspirate fluid over the 6-year period from 2006 to 2011 were retrospectively reviewed. Aspirate fluid culture results were compared to intraoperative cultures, which were used as the "gold standard" for diagnosing SSI. The diagnostic value was evaluated by determining the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of aspirate fluid cultures. Clinical presentation, patient demographics, comorbidities, and laboratory values were reviewed for association with infection risk.

RESULTS

Eleven of thirty patients undergoing CT-guided aspiration were subsequently confirmed to have SSI through positive cultures. Wound drainage, wound erythema, elevated ESR, and cloudiness of aspirate fluid were associated with SSI. The sensitivity and specificity of aspirate cultures were 36.4 and 89.5%, respectively, and the respective positive predictive value (PPV) and negative predictive value (NPV) were 66.7 and 70.8%.

CONCLUSIONS

Cloudy aspirate fluid was highly suggestive of infection, while wound erythema, drainage, and elevated ESR were also suggestive of SSI. CT-guided aspirations are a useful adjunct tool in evaluating for SSI but further studies are necessary before it can be considered a stand-alone diagnostic procedure.

Do serologic and synovial tests help diagnose infection in revision hip arthroplasty with metal-on-metal bearings or corrosion?

BACKGROUND

The diagnosis of periprosthetic joint infection (PJI) in patients with failed metal-on-metal (MoM) bearings and corrosion reactions in hip arthroplasties can be particularly difficult, because the clinical presentation of adverse local tissue reactions may mimic that of PJI, because it can also occur concurrently with PJI, and because common laboratory tests used to diagnose PJI may be elevated in patients with MoM THAs.

QUESTIONS/PURPOSES

We sought to determine the test properties of the serum erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), synovial fluid white blood cell (WBC) count, and synovial fluid differential (percent polymorphonuclear cells [PMNs]) in diagnosing PJI in either MoM hips undergoing revision for a variety of indications or in non-MoM hips undergoing revision for either corrosion reaction or full-thickness wear. Additionally, we sought to describe how MoM bearings, metal debris, and corrosion reactions can confound the analysis of the synovial fluid WBC count and affect its diagnostic use for PJI.

METHODS

We reviewed 150 revision hips meeting specified inclusion criteria (92 MoM total hips, 19 MoM hip resurfacings, 30 non-MoM bearings with corrosion, and nine full-thickness bearing surface wear with metallosis). In our review, we diagnosed 19 patients as infected using Musculoskeletal Infection Society (MSIS) criteria. Mean laboratory values were compared between infected and not infected patients and receiver operator characteristic curves were generated with an area under the curve (AUC) to determine test performance and optimal cutoffs.

RESULTS

After excluding the inaccurate synovial fluid samples, the synovial fluid WBC count (performed accurately in 102 patients) was the best test for the diagnosis of PJI (AUC=98%, optimal cutoff 4350 WBC/μL) followed by the differential (performed accurately in 102 patients; AUC=90%, optimal cutoff 85% PMN). The ESR (performed in 131 patients) and CRP (performed in 129 patients) both had good sensitivity (83% and 94%, respectively). Patients meeting MSIS criteria for PJI had higher mean serum ESR, CRP, synovial fluid WBC count, and differential than those not meeting MSIS criteria (p<0.05 for all). An observer blinded to the MSIS diagnosis of the patient assessed the synovial fluid samples for inaccuracy secondary to metal or cellular debris. Synovial fluid sample "inaccuracy" was defined as the laboratory technician noting the presence of metal or amorpous material, fragmented cells, or clots, or the sample having some defect preventing an automated cell count from being performed. Of the 141 patients who had a synovial fluid sample initially available for review, 47 (33%) had a synovial fluid sample deemed to be inaccurate. A synovial fluid WBC count was still reported; however, 35 of these 47 hips (75%) and 11 of these 35 (31%) were falsely positive for infection.

CONCLUSIONS

The diagnosis of PJI is extremely difficult in patients with MoM bearings or corrosion and the synovial fluid WBC count can frequently be falsely positive and should be relied on only if a manual count is done and if a differential can be performed. A more aggressive approach to preoperative evaluation for PJI is recommended in these patients to allow for careful evaluation of the synovial fluid specimen, the integration of synovial fluid culture results, and repeat aspiration if necessary.

LEVEL OF EVIDENCE

Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Is synovial C-reactive protein a useful marker for periprosthetic joint infection?

BACKGROUND

Serum C-reactive protein (CRP) is a general marker of inflammation, and recent studies suggest that measurement of CRP in synovial fluid may be a more accurate method for diagnosing periprosthetic joint infection (PJI).

QUESTIONS/PURPOSES

We aimed to (1) determine if there is a correlation between serum and synovial CRP values, (2) establish cutoff values for diagnosing infection based on serum and synovial CRP, and (3) compare the utility of measuring CRP in synovial fluid versus serum for the diagnosis of PJI using standard assay equipment available at most hospitals.

METHODS

Between February 2011 and March 2012, we invited all 150 patients scheduled for revision TKA (84) or THA (66) to participate in this prospective study, of whom 100% agreed. Data ultimately were missing for 31 patients, leaving 60 patients undergoing revision TKA and 59 undergoing revision THA (71% and 89% of the original group, respectively) for whom CRP level was measured in serum and synovial fluid samples. Patients were deemed to have a PJI (32) or no infection (87) using Musculoskeletal Infection Society criteria. Serum and synovial CRP levels were assayed using the same immunospectrophotometer and the correlation coefficient was calculated. Receiver operating characteristic curve analyses were performed to compare utility in diagnosing PJI, which included area under the curve, diagnostic threshold, and test sensitivity, specificity, predictive values, and accuracy. In 22 of 150 patients (14.7%), synovial CRP could not be measured because the sample was too viscous or hemolyzed.

RESULTS

In the analyzed 119 samples, there was a strong correlation (r = 0.76; p < 0.001) between synovial and serum CRP. The area under the curve was 0.90 both for the synovial fluid (95% CI, 0.82-0.97) and serum (95% CI, 0.84-0.96) CRP assays. The diagnostic thresholds were 6.6 mg/L for synovial fluid and 11.2 mg/L for serum. Sensitivities, specificities, positive predictive value, negative predictive value, and accuracies were similar for synovial fluid and serum assays.

CONCLUSIONS

Although recent studies have suggested a superiority of synovial fluid CRP over serum CRP for the diagnosis of PJI, we found that measurement of CRP in synovial fluid rather than serum using readily available assay equipment does not offer a diagnostic advantage in detection of PJIs.

LEVEL OF EVIDENCE

Level II, diagnostic study. See the Instructions to Authors for a complete description of levels of evidence.

The host response: Toll-like receptor expression in periprosthetic tissues as a biomarker for deep joint infection

BACKGROUND

Toll-like receptors (TLRs) 1 and 6 are consistent molecular indicators of the host inflammatory response against bacterial infection. Our aims were to determine whether TLR elevation could be detected in infected periprosthetic tissues and to assess the utility of these biomarkers as tests for detecting a periprosthetic joint infection.

METHODS

Fifty-nine patients undergoing revision total joint arthroplasty (twenty-seven hips and thirty-two knees) were prospectively evaluated for periprosthetic joint infection according to currently recommended diagnostic criteria. Nine patients were excluded because of insufficient work-up, leaving fifty available for study. Of these, twenty-one were categorized as infected and twenty-nine as noninfected. Periprosthetic tissues were collected intraoperatively, and total RNA was extracted by standard techniques. Expression of TLR messenger RNAs was assessed by first-strand complementary DNA synthesis from 1 μg of total RNA followed by real-time PCR (polymerase chain reaction). Results were normalized relative to the housekeeping gene GAPDH (glyceraldehyde 3-phosphate dehydrogenase). Expression of TLRs 1, 6, and 10 in the infected and noninfected groups was compared with use of the Student t test. The receiver operating characteristic curve, area under the curve (AUC), sensitivity, specificity, positive likelihood ratio (LR+), and negative likelihood ratio (LR-) were calculated to determine the accuracy of each TLR for predicting periprosthetic joint infection at its optimal diagnostic threshold.

RESULTS

Mean TLR1 mRNA expression was significantly elevated in infected compared with noninfected samples (0.600 compared with 0.005, p = 0.0003); the same was true of TLR6 (0.208 compared with 0.0165, p = 0.0059) but not of TLR10 (0.00019 compared with 0.00014, p = 0.6238). The AUC was 0.995 for TLR1, 0.883 for TLR6, and 0.546 for TLR10. The optimal threshold for diagnosing periprosthetic joint infection was 0.0924 for TLR1 (sensitivity = 95.2%, specificity = 100%, LR+ = 13.80, LR- = 0.91) and 0.0215 for TLR6 (sensitivity = 85.7%, specificity = 82.8%, LR+ = 4.98, LR- = 0.83).

CONCLUSIONS

In our pilot study, TLR1 expression in periprosthetic tissues most accurately predicted periprosthetic joint infection. This measure of the host response may be particularly helpful in detecting culture-negative infections and avoiding false positives resulting from contamination.

LEVEL OF EVIDENCE

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Endoglin (CD105) expression differentiates between aseptic loosening and periprosthetic joint infection after total joint arthroplasty

The differentiation between aseptic loosening and periprosthetic joint infection (PJI) after total joint arthroplasty is essential for successful therapy. A better understanding of pathogenesis of aseptic loosening and PJI may help to prevent or treat these complications. Previous investigations revealed an increased vascularization in the periprosthetic membrane in cases of PJI via PET signals. Based on these findings our hypothesis was that PJI is associated with an increased neovascularization in the periprosthetic membrane.

Tissue samples from periprosthetic membranes of the bone-implant interface were investigated histologically for inflammation, wear particles, vascularization and fibrosis. To identify vascular structures antibodies against CD 31, CD 34, factor VIII and CD 105 (endoglin) were applied for immunohistochemical investigations. According to a consensus classification of Morawietz the tissue samples were divided into four types: type I (wear particle induced type, n = 11), type II (infectious type, n = 7), type III (combined type, n = 7) and type IV (indeterminate type, n = 7).

Patients with PJI (type II) showed a pronounced infiltration of neutrophil granulocytes in the periprosthetic membrane and an enhanced neovascularization indicated by positive immunoreaction with antibodies against CD 105 (endoglin). Tissue samples classified as type I, type III and type IV showed significantly less immune reaction for CD 105.

In cases of aseptic loosening and PJI vascularization is found in different expression in periprosthetic membranes. However, in aseptic loosening, there is nearly no neovascularization with CD 105-positive immune reaction. Therefore, endoglin (CD 105) expression allows for differentiation between aseptic loosening and PJI.

Synovial IL-6 as inflammatory marker in periprosthetic joint infections

We analyzed serum and synovial biomarkers of 69 patients. 31 of them suffered from a periprosthetic joint infection (PJI) and 38 from aseptic arthralgia after total joint arthroplasty. We used Receiver-Operating-Characteristic-curves to calculate the Area-under-the-curve (AUC), cutoff-values, positive (+LR), negative (-LR) and interval-Likelihood-Ratios (iLR) for predicting a PJI. The most significant parameter was synovial interleukin-6 (IL-6) (cutoff-value ≥ 30,750 pg/ml, AUC = 0.959, SE = 90.0%, SP = 94.7%, +LR = 17.27), followed by synovial lactate (cutoff-value ≥ 8.3 mmol/l, AUC = 0.844, SE = 71.4%, SP=88.0%, +LR = 5.95), and synovial glucose (cutoff-value ≤ 44 mg/dl, AUC = 0.829, SE = 79.2%, SP = 78.6%, +LR = 3.69). IL-6 ≥ 30,750 pg/ml and lactate ≥ 10 mmol/l make a PJI very likely, IL-6 <10,000pg/ml or lactate <4.3 mmol/l makes a PJI very unlikely. If none of these thresholds are met, physicians should use the iLR of IL-6, glucose and lactate to estimate the likelihood of PJI.

Comparison of bacterial results from conventional cultures of the periprosthetic membrane and the synovial or pseudocapsule during hip revision arthroplasty

INTRODUCTION

Bacterial identification is essential to diagnose and treat a revision for prosthetic loosening of an infected hip. The purpose of this study was to determine whether conventional cultures from the periprosthetic membrane are superior to synovial/pseudocapsule samples in the diagnosis of infection in hip revision arthroplasty.

MATERIALS AND METHODS

We performed a prospective study including all hip revisions from October 2009 to October of 2011. Once the implants were removed and prior to the administration of the antibiotic prophylaxis, six periprosthetic samples from different sites were sent to the laboratory for culturing: two periprosthetic fluid samples, two solid material (synovial/pseudocapsule) samples and two swabs. Once the six samples were taken, antibiotic prophylaxis was administered and just as the implant was removed, two more solid samples of the periprosthetic membrane were obtained.

RESULTS

Of a total of 86 hip revision surgeries, 22 were considered septic revisions postoperatively, of which 16 resulted in positive cultures. Of these 16 revisions, 14 obtained the same microbiologic diagnostic when considering either the synovial/pseudocapsule culture results or the solid membrane sample.

CONCLUSIONS

We conclude that the membrane sample for a conventional culture is not superior to the synovial/pseudocapsule sample in detecting microorganisms.

Acute hematogenous infection following total hip and knee arthroplasty

Forty consecutive patients (42 joints; 22 TKA, 20 THA) treated for acute hematogenous infections were reviewed. All patients underwent irrigation and debridement and exchange of the modular components. At a mean of 56 months (range, 25-124 months) recurrent infection, requiring surgery, developed in 9 of the 42 joints (21%); 8 of the 9 recurrent infections were in patients with a staphylococcal infection (P = 0.0004). Ten of the 40 patients (25%) died within 2 years of infection. Irrigation and debridement for the treatment of an acute hematogenous infection was successful in the majority of patients (76% survivorship at 2 years). Non-staphylococcal infections had a particularly low failure rate (96% survivorship at 2 years). The 2 year mortality rate among this subset of patients was strikingly high.

The 2013 Frank Stinchfield Award: Diagnosis of infection in the early postoperative period after total hip arthroplasty

BACKGROUND

Diagnosis of periprosthetic joint infection (PJI) can be difficult in the early postoperative period after total hip arthroplasty (THA) because normal cues from the physical examination often are unreliable, and serological markers commonly used for diagnosis are elevated from the recent surgery.

QUESTIONS/PURPOSES

The purposes of this study were to determine the optimal cutoff values for erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), synovial fluid white blood cell (WBC) count, and differential for diagnosing PJI in the early postoperative period after primary THA.

METHODS

We reviewed 6033 consecutive primary THAs and identified 73 patients (1.2%) who underwent reoperation for any reason within the first 6 weeks postoperatively. Thirty-six of these patients were infected according to modified Musculoskeletal Infection Society criteria. Mean values for the diagnostic tests were compared between groups and receiver operating characteristic curves generated along with an area under the curve (AUC) to determine test performance and optimal cutoff values to diagnose infection.

RESULTS

The best test for the diagnosis of PJI was the synovial fluid WBC count (AUC = 98%; optimal cutoff value 12,800 cells/μL) followed by the CRP (AUC = 93%; optimal cutoff value 93 mg/L), and synovial fluid differential (AUC = 91%; optimal cutoff value 89% PMN). The mean ESR (infected = 69 mm/hr, not infected = 46 mm/hr), CRP (infected = 192 mg/L, not infected = 30 mg/L), synovial fluid WBC count (infected = 84,954 cells/μL, not infected = 2391 cells/μL), and differential (infected = 91% polymorphonuclear cells [PMN], not infected = 63% PMN) all were significantly higher in the infected group.

CONCLUSIONS

Optimal cutoff values for the diagnosis of PJI in the acute postoperative period were higher than those traditionally used for the diagnosis of chronic PJI. The serum CRP is an excellent screening test, whereas the synovial fluid WBC count is more specific.