Joshua S. Bingham

The Alpha Defensin-1 Biomarker Assay can be Used to Evaluate the Potentially Infected Total Joint Arthroplasty

BackgroundDiagnosing a periprosthetic joint infection (PJI) requires a complex approach using various laboratory and clinical criteria. A novel approach to diagnosing these infections uses synovial fluid biomarkers. Alpha defensin-1 (AD-1) is one such synovial-fluid biomarker. However little is known about the performance of the AD-1 assay in the diagnosis of PJI.Questions/purposesWe sought to (1) determine the sensitivity and specificity of the AD-1 assay in a population of patients being evaluated for PJI, using the Musculoskeletal Infection Society (MSIS) criteria as the reference standard, and (2) compare the AD-1 assay with other currently available clinical tests, specifically cell count, culture, erythrocyte sedimentation rate, and C-reactive protein.Patients and MethodsA retrospective review was performed of all patients undergoing workup for a PJI at our institution from January to June 2013. Sixty-one AD-1 assays were done in 57 patients. The group included 51 patients with 55 painful joints and six patients who underwent aspiration before second-stage reimplantation. Patients were considered to have a PJI if they met the MSIS criteria. We calculated the sensitivity and specificity of the AD-1 synovial fluid assay, and compared it with the sensitivity and specificity of the synovial fluid cell count, culture, erythrocyte sedimentation rate, and C-reactive protein. There were 19 diagnosed infections in the 61 aspirations, with 21 positive and 40 negative AD-1 assays. There were two false positive and no false negatives AD-1 assays.ResultsThe sensitivity and specificity for the AD-1 assay were 100% (95% CI, 79%–100%) and 95% (95% CI, 83%–99%), respectively. The sensitivity and specificity of the other tests ranged from 68% to 95% and 66% to 88%, respectively. The AD-1 assay results outperformed the other tests but did not reach statistical significance except for the sensitivity of the erythrocyte sedimentation rate.ConclusionThe sensitivity and specificity of the synovial fluid AD-1 assay exceeded the sensitivity and specificity of the other currently available clinical tests evaluated here but did not reach significance. The AD-1 assay offers another test with high sensitivity and specificity for diagnosing a PJI especially in the case where the diagnosis of PJI is uncertain, but larger studies will be needed to determine significance and cost effectiveness.Level of EvidenceLevel III, diagnostic study. See the Instructions for Authors for a complete description of levels of evidence.

The Alpha-Defensin Test for Diagnosing Periprosthetic Joint Infection in the Setting of an Adverse Local Tissue Reaction Secondary to a Failed Metal-on-Metal Bearing or Corrosion at the Head-Neck Junction.

BACKGROUND In patients with adverse local tissue reaction (ALTR) secondary to a failed metal-on-metal (MoM) bearing or corrosion at the head-neck junction in a metal-on-polyethylene bearing, ruling in or out periprosthetic joint infection (PJI) can be challenging. Alpha-defensin has emerged as an accurate test for PJI. The purpose of this multicenter, retrospective study was to evaluate the accuracy of the alpha-defensin synovial fluid test in detecting PJI in patients with ALTR. METHODS We reviewed medical records of 26 patients from 3 centers with ALTR that had an alpha-defensin test performed. Patients were assessed for PJI using the Musculoskeletal Infection Society criteria. Thirteen of these subjects had MoM total hip arthroplasty, 9 had ALTR secondary to head-neck corrosion, and 4 had MoM hip resurfacing. RESULTS Only 1 of the 26 patients met Musculoskeletal Infection Society criteria for infection. However, 9 hips were alpha-defensin positive, including 1 true positive and 8 that were falsely positive (31%). All 8 of the false positives were also Synovasure positive, although 5 of 8 had an accompanying warning stating the results may be falsely positive due to a low synovial C-reactive protein value. CONCLUSION Similar to synovial fluid white blood cell count, alpha-defensin testing is prone to false-positive results in the setting of ALTR. Therefore, we recommend an aggressive approach to ruling out PJI including routine aspiration of all hips with ALTR before revision surgery to integrate the synovial fluid blood cell count, differential, cultures and adjunctive tests like alpha-defensin to allow for accurate diagnosis preoperatively.

Management of the Infected Total Knee Arthroplasty

There are now several approaches to the infected knee, but complete eradication of infection seems to be near impossible. The treatment protocols include incision and drainage, immediate exchange, and two-stage reimplantation. There are multiple modifications to these approaches that do help to decrease the overall incidence of infection.

An Evidence-Based Clinical Prediction Algorithm for the Musculoskeletal Infection Society Minor Criteria

BACKGROUND The diagnosis of a periprosthetic joint infection (PJI) remains a clinical challenge, as there is no uniformly accepted gold standard. In 2011, the Musculoskeletal Infection Society (MSIS) convened a work group to create a standardized definition for a PJI that could be universally adopted. Based on the MSIS criteria, the diagnosis of a PJI can be made with 1 of the 2 major criteria, or 3 of the 5 minor criteria. The purpose of this study was to determine the likelihood of having a PJI based on the number of positive minor criteria and thereby develop a prediction algorithm for differentiating between a chronic PJI and a non-PJI based on the number of positive MSIS minor criteria. METHODS We retrospectively reviewed 297 patients who presented to a tertiary care center between 2004 and 2014 with a failed total joint arthroplasty and subsequently underwent a PJI workup to exclude chronic PJI. Patients were divided into 2 groups: (1) PJI group and (2) non-PJI group. Patients who had a positive PJI workup and subsequently underwent a 2-stage revision for infection were included in the PJI group. Patients who had a negative clinical and diagnostic workup were included in the non-PJI group. One hundred eighty-two patients met the criteria for inclusion in the study, 91 in each group. Univariate and multiple logistic regression analyses were used to evaluate 21 independent variables in each of the 2 groups. A prediction algorithm for differentiating between a chronic PJI and a non-PJI based on independent multivariate variables was created. RESULTS Patients who had a PJI differed significantly (P < .05) from those who did not have a PJI with regard to 10 independent variables, which included all the MSIS minor criteria we evaluated. Five independent multivariate variables were identified to differentiate between the 2 groups: positive cultures, elevated synovial white blood cell count, elevated synovial polymorphonuclear neutrophil percentage, elevated erythrocyte sedimentation rate, and elevated C-reactive protein. The predictive probability of a PJI for all 32 combinations of these 5 variables was: 3.6% for 1 positive variable, 19.3% for 2, 58.7% for 3, 83.8% for 4, and 97.8% for 5. The chi-squared test for trend and the area under the receiver-operating characteristic curve (0.977) suggest that the model is highly predictive, with an excellent diagnostic performance in identifying a PJI. CONCLUSIONS Diagnosing a PJI remains a clinical challenge as there is no gold standard for diagnosis. The development of the MSIS criteria, which is based on a consensus of over 400 of the worlds experts in musculoskeletal infection, was a major step forward in defining the diagnosis of a PJI. However, to our knowledge, the likelihood of having a PJI based on the number of positive minor criteria has yet to be validated or quantified. Of the 20 independent variables that were evaluated, 10 were found to be significantly associated with a PJI, including all the MSIS minor criteria evaluated. In addition, a diagnostic prediction algorithm was constructed to determine the likelihood of a PJI based on 5 binary independent multivariate variables. The relationship was also examined with a receiver-operating characteristic curve analysis. The area under the curve was 0.98, indicating excellent diagnostic performance for the MSIS minor criteria in identifying a PJI. LEVEL OF EVIDENCE III.

Surgeon Personal Protection: An Underappreciated Benefit of Positive-pressure Exhaust Suits

Background Positive-pressure exhaust suits cost more than standard surgical gowns, and recent evidence suggests that they do not decrease infection risk. As a result, some hospitals and surgeons have abandoned positive-pressure exhaust suits in favor of less expensive alternatives. We propose that in addition to their original purpose of decreasing infection rates, positive-pressure exhaust suits may also improve personal protection for the surgeon and assistants, perhaps justifying their added costs. Questions/purposes (1) Do positive-pressure exhaust suits decrease exposure to particulate matter during TKA? (2) What areas covered by gowning systems are at risk of exposure to particulate matter? Methods Three surgical gowning systems were tested: (1) surgical gown, face mask, surgical skull cap, protective eyewear; (2) surgical gown, face mask, surgical protective hood, protective eyewear; and (3) positive-pressure exhaust suit. For each procedure, a cadaver knee was injected intraarticularly and intraosseously with a 5-µm fluorescent powder mixed with water (1 g/10 mL). After gowning in the standard sterile fashion, the primary surgeon and two assistants performed two TKAs with each gowning system for a total of six TKAs. After each procedure, three independent observers graded skin exposure of each surgical participant under ultraviolet light using a standardized scale from 0 (no exposure) to 4 (gross exposure). Statistical analysis was performed using Friedman’s and Nemenyi tests. The interrater reliability for the independent observers was also calculated. Results The positive-pressure exhaust suits had less surgeon and assistant exposure compared with other systems (p < 0.001). The median overall exposure grade for each gowning system was 4 for System 1 (range, 3–4), 2.5 for System 2 (range, 2–3), and 0 for System 3 (range, 0–0). In pairwise comparisons between gowning systems, the positive-pressure exhaust suits had less exposure than gowning System 1 (difference of medians: 4, p < 0.001) and gowning System 2 (difference of medians: 2.5, p = 0.038). There was no difference found in exposure between Systems 1 and 2 (difference of medians: 1.5, p = 0.330). When gowning Systems 1 and 2 were removed, particulate matter was found in places that were covered such as the surgeon’s beard, lips, inside the nostrils, behind the protective eyewear around the surgeon’s eye, and in both eyebrows and eyelashes. Conclusions The positive-pressure exhaust suits provided greater personal protection with each procedure than the other two gowning systems. Clinical Relevance With conventional gowns, particulate matter was found in the surgeon’s eyelashes, under the face mask around the mouth, and inside the nostrils. Despite recent evidence that certain types of positive-pressure exhaust suits may not decrease infection, there is a clear benefit of surgeon protection from potentially infectious and harmful patient substances. Despite their added costs, hospitals and surgeons should weigh this protective benefit when considering the use of positive-pressure exhaust suits.

A dedicated anticoagulation clinic does not improve postoperative management of warfarin after total joint arthroplasty

Background Periprosthetic joint infections (PJIs) are devastating complications. Excessive anticoagulation with warfarin is an independent risk factor for PJIs. The use of a dedicated anticoagulation clinic to improve warfarin management has not been proven. Methods Between 2006 and 2014, we identified 92 patients who were placed on postoperative warfarin, and later developed PJI. These patients were compared to 313 patients who underwent total joint arthroplasty placed on warfarin without developing PJI. Patients were included if they had no history of a venous thromboembolic event, were warfarin naive, and enrolled in the anticoagulation clinic. A univariate analysis compared independent variables, and statistical analysis was performed using Students t-test and Pearson chi-square test for continuous and categorical variables. Results Thirty-six PJI patients and 297 control patients met the inclusion criteria. The venous thromboembolism rate was 2.1%. At discharge, 82% of all patients were subtherapeutic. Patients were within their target international normalized ratio (INR) range 26.7% of the time. The mean INR in the initial postoperative period for the PJI group was 1.46 and 1.29 in the control group (P < .001). In the acute postoperative period, 13.3% of the knee PJI group were therapeutic or supratherapeutic compared with 3.5% in the knee control group (P = .002). Conclusions Despite utilization of a dedicated anticoagulation clinic, patients were only within their target INR range 27% of the time. Total knee arthroplasty patients who developed a PJI were more likely to be therapeutic or supratherapeutic in the initial postoperative period. Consequently, the risks associated with warfarin as a venous thromboembolism prophylaxis may outweigh the potential benefits.

Anterior Cruciate Ligament Tunnel Placement Using the Pathfinder Guide

Reconstruction techniques for the anterior cruciate ligament (ACL) have evolved considerably over the past 3 decades. The femoral tunnel is most commonly made via a transtibial or separate anteromedial portal approach. Benefits and drawbacks for each of these techniques exist. Improper tunnel placement is the cause of failure for ACL reconstruction 70% of the time. We present a hybrid technique for femoral tunnel placement using the Pathfinder ACL guide, which attempts to give the surgeon many of the benefits of both the transtibial and anteromedial portal techniques without the drawbacks.