In Vivo Intra-Articular Antibiotic Concentrations at 24 Hours After TKA Fall Below the Minimum Inhibitory Concentration for Most Bacteria: A Randomized Study of Commercially Available Bone Cement.

BACKGROUND: The use of antibiotic-loaded bone cement (ALBC) to help reduce the risk of infection after primary total knee arthroplasty (TKA) is controversial. There is a paucity of in vivo data on the elution characteristics of ALBC. We aimed to determine whether the antibiotic concentrations of 2 commercially available ALBCs met the minimum inhibitory concentration (MIC) and minimum biofilm eradication concentration (MBEC) for common infecting organisms. METHODS: Forty-five patients undergoing TKA were randomized to receive 1 of the following: bone cement without antibiotic (the negative control; n = 5), a commercially available formulation containing 1 g of tobramycin (n = 20), or a commercially available formulation containing 0.5 g of gentamicin (n = 20). Intra-articular drains were placed, and fluid was collected at 4 and 24 hours postoperatively. An automated immunoassay measuring antibiotic concentration was performed, and the results were compared against published MIC and MBEC thresholds. RESULTS: The ALBC treatment groups were predominantly of White (65%) or Black (32.5%) race and were 57.5% female and 42.4% male. The mean age (and standard deviation) was 72.6 ± 7.2 years in the gentamicin group and 67.6 ± 7.4 years in the tobramycin group. The mean antibiotic concentration in the tobramycin group was 55.1 ± 37.7 µg/mL at 4 hours and 19.5 ± 13.0 µg/mL at 24 hours, and the mean concentration in the gentamicin group was 38.4 ± 25.4 µg/mL at 4 hours and 17.7 ± 15.4 µg/mL at 24 hours. Time and antibiotic concentration had a negative linear correlation coefficient (r = -0.501). Most of the reference MIC levels were reached at 4 hours. However, at 24 hours, a considerable percentage of patients had concentrations below the MIC for many common pathogens, including Staphylococcus epidermidis (gentamicin: 65% to 100% of patients; tobramycin: 50% to 85%), methicillin-sensitive Staphylococcus aureus (gentamicin: 5% to 90%; tobramycin: 5% to 50%), methicillin-resistant S. aureus (gentamicin: 5% to 65%; tobramycin: 50%), Streptococcus species (gentamicin: 10% to 100%), and Cutibacterium acnes (gentamicin: 10% to 65%; tobramycin: 100%). The aforementioned ranges reflect variation in the MIC among different strains of each organism. Gentamicin concentrations reached MBEC threshold values at 4 hours only for the least virulent strains of S. aureus and Escherichia coli. Tobramycin concentrations did not reach the MBEC threshold for any of the bacteria at either time point. CONCLUSIONS: The elution of antibiotics from commercially available ALBC decreased rapidly following TKA, and only at 4 hours postoperatively did the mean antibiotic concentrations exceed the MIC for most of the pathogens. Use of commercially available ALBC may not provide substantial antimicrobial coverage following TKA. LEVEL OF EVIDENCE: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Plasma D-Dimer Is a Promising Marker to Guide Timing of Reimplantation: A Prospective Cohort Study.

BACKGROUND: Two-stage exchange arthroplasty remains the preferred surgical treatment for chronic periprosthetic joint infection. Currently, there is no single reliable marker to determine the optimal timing for reimplantation. The purpose of this prospective study was to assess the diagnostic utility of plasma D-dimer and other serological markers in predicting successful control of infection following reimplantation. METHODS: This study enrolled 136 patients undergoing reimplantation arthroplasty between November 2016 and December 2020. Strict inclusion criteria were applied including the need for a two-week "antibiotic holiday" prior to reimplantation. A total of 114 patients were included in the final analysis. Plasma D-dimer, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and fibrinogen were measured preoperatively. Treatment success was defined using the Musculoskeletal Infection Society Outcome-Reporting Tool. Receiver operating characteristic curves were used to assess the prognostic accuracy of each biomarker in predicting failure following reimplantation at a minimum 1-year follow-up. RESULTS: Treatment failure occurred in 33 patients (28.9%) at a mean follow-up of 3.2 years (range, 1.0 to 5.7). Median plasma D-dimer was significantly higher in the treatment failure group (1,604 versus 631 ng/mL, P < .001), whereas median CRP, ESR, and fibrinogen were not significantly different between the success and failure groups. Plasma D-dimer demonstrated the best diagnostic utility (area under the curve [AUC] 0.724, sensitivity 51.5%, specificity 92.6%), outperforming ESR (AUC 0.565, sensitivity 93.3%, specificity 22.5%), CRP (AUC 0.541, sensitivity 87.5%, specificity 26.3%), and fibrinogen (AUC 0.485, sensitivity 30.4%, specificity 80.0%). Plasma D-dimer level of ≥1,604 ng/mL was identified as the optimal cutoff that predicted failure following reimplantation. CONCLUSION: Plasma D-dimer was superior to serum ESR, CRP, and fibrinogen in predicting failure after the second stage of a two-stage exchange arthroplasty for periprosthetic joint infection. Based on the findings of this prospective study, plasma D-dimer may be a promising marker in assessing the control of infection in patients undergoing reimplantation surgery. LEVEL OF EVIDENCE: Level II.

Mark Coventry Award: Human Knee Has a Distinct Microbiome: Implications for Periprosthetic Joint Infection.

BACKGROUND: Pathogens causing prosthetic joint infection (PJI) are thought to gain access to the knee during surgery or from a remote site in the body. Recent studies have shown that there is a distinct microbiome in various sites of the body. This prospective study, and first of its kind, was set up to investigate the presence of possible microbiome in human knee and compare the profile in different knee conditions. METHODS: We obtained synovial fluid from 65 knees (55 patients) with various conditions that included normal knee, osteoarthritis (OA), aseptic revision, and those undergoing revision for PJI. The contralateral knee of patients who had a PJI were also aspirated for comparison. A minimum of 3 milliliters of synovial fluid was collected per joint. All samples were aliquoted for culture and next-generation sequencing analysis. RESULTS: The highest number of species was found in native osteoarthritic knees (P ≤ .035). Cutibacterium, Staphylococcus, and Paracoccus species were dominant in native nonosteoarthritic knees, and meanwhile a markedly high abundance of Proteobacteria was observed in the osteoarthritic joints. Moreover, the contralateral and aseptic revision knees showed a similar trend in bacterial composition (P = .75). The sequencing analysis of patients who had PJI diagnosis, confirmed the culture results. CONCLUSION: Distinct knee microbiome profiles can be detected in patients who have OA and other knee conditions. The distinct microbiome in the knee joint and the close host-microbe relationships within the knee joint may play a decisive role in the development of OA and PJI.

Sterile Setup Table in the Operating Room Is Not So Sterile.

BACKGROUND: One of the important factors for surgical site infection prevention is the implementation of an ultraclean operating room. This study was designed to evaluate back-table sterility during total joint arthroplasty. METHODS: This prospective study includes 52 patients undergoing primary total joint arthroplasty between November 2021 and January 2022. A total of 4 swabs (2 air swabs and 2 table swabs) were obtained for each case, at the conclusion of surgery and prior to the takedown of drapes. One swab from each set was sent for culture, and the other was sent for next-generation sequencing (NGS) analysis. RESULTS: Among 104 back-table swabs, a total of 13 (12.5%) organisms were isolated. Of these, 7 organisms were isolated by culture and 6 by NGS. No microorganisms were isolated by both culture and NGS from back-table swabs. Among 104 air swabs, a total of 11 (10.6%) organisms were isolated. Of these, 6 microorganisms were isolated by culture and 5 by NGS. In 4 of the 104 swabs, both culture- and NGS-isolated organisms were from air swabs. Of the 104 (12.5%) back-table and air swabs, 13 were culture positive. While more than 1 pathogen was identified in 2 air swabs, all back-table swabs were monomicrobial by culture. Pathogens were identified from 11 of 104 (10.6%) swabs by NGS, while more than 1 pathogen was identified in 4 swabs (2 air and 2 back table). CONCLUSION: The findings of this study raise an important issue that the surgical field including the sterile table setup for instruments is not "sterile" and can harbor pathogens.