Efficacy of intraoperative cultures obtained during revision total hip arthroplasty

Reinfection Patterns Following Two-Stage Exchange for Periprosthetic Joint Infection: A Retrospective Analysis

BACKGROUND

Periprosthetic joint infection (PJI) is a challenging complication following total joint arthroplasty. A two-stage exchange has been the gold standard in the treatment of chronic PJI. However, when this fails, further treatment options become limited. In patients who fail two-stage exchange, the reinfecting organism is different from the original in 50 to 80% of the occurrences. This study aimed to understand reinfection patterns in an attempt to better predict reinfecting organisms to improve the management of PJI.

METHODS

A retrospective query of our institution's PJI registry identified 185 patients (188 procedures, 110 knees, and 78 hips) who underwent a first-time two-stage exchange for culture-positive chronic PJI of total knee and hip arthroplasties from January 2010 to December 2020. Patients who had polymicrobial infections, culture-negative results, or fungal infections were excluded. The primary outcome variable was reoperation for reinfection and comparing the index organism to the reinfecting organisms.

RESULTS

Of the 188 procedures, 31 (16.5%) failed due to reinfection. Among reinfections, 30 (96.8%) were gram-positive, with Staphylococcus aureus species accounting for 22 (71.0%) of the cases. The most common organisms cultured were for methicillin-sensitive S. Aureus, methicillin-resistant S. Aureus, coagulase-negative staphylococcus, and streptococcus. Of reinfections, 19 (61.3%) had a different organism, eight (25.8%) had the same organism, and four (12.9%) were culture-negative. Patients experiencing reinfection were significantly younger (P = 0.012), with no other patterns or predictors identified.

CONCLUSIONS

The majority of reinfections following a two-stage exchange for PJI occur with a different organism than the index infection. We did not find a reliable method to predict the reinfecting organisms based on the initial infecting organism alone. However, the same four gram-positive organisms were the most frequently encountered in both the primary infection and the reinfection. Further research is required to understand factors contributing to reinfection and help guide prevention strategies.

Unexpected Positive Cultures in Presumed Aseptic Revision Total Hip Arthroplasty

Background:

Occult infection may be the underlying cause for a number of presumed aseptic revision total hip arthroplasty (THA) because certain periprosthetic joint infections (PJIs) can remain asymptomatic for years and present with component loosening and weight-bearing pain in the absence of any clinical signs and symptoms of infection. There is no consensus in the literature regarding the interpretation, treatment, and clinical outcomes of unexpected positive cultures (UPCs) during aseptic revision THA.

Methods:

Four main databases were searched between January 2000 and January 2023. By pooling the UPC rates from the included studies, an overall UPC rate was calculated. We examined variables reported in more than 2 articles for possible associations with UPC.

Results:

Twenty-two articles were included. UPC prevalence in presumed aseptic revision THA (7,449 cases) was 15.06% (95% confidence interval [CI]: 11.05-20.19). In regards to unexpected culture positivity and culture method or medium, conventional cultures reported a 17.2% incidence, implant sonication 19.6%, and polymerase chain reaction 12.6%. Coagulase-negative staphylococci and Cutibacterium acnes were the most common pathogens (prevalence [95% CI]: 54.4% [44.9%-63.6%] and 9.1% [5.1%-15.8%]). Polymicrobial cultures were observed in 11.6% [7.318.0%] of UPCs. UPC cases were found to include more males than culture-negative THA patients (odds ratio [OR] [95% CI]: 1.36 [1.02-1.83]). Age, body mass index, American Society of Anesthesiology, loosening, previous revision, diabetes mellitus, and rheumatoid arthritis did not show a significant association with UPC incidence (p > 0.05). The all-cause revision and PJI rate were significantly higher in those having an UPC (OR [95% CI]: 1.40 [1.09-1.80], p = 0.009 and OR [95% CI]: 1.97 [1.22-3.18], p = 0.005).

Conclusions:

Isolating organisms through intraoperative culture is common in patients undergoing aseptic revision THA. This diagnostic step is crucial to properly investigate and exclude the possibility of an occult PJI. It should be noted that our results are prone to limitations of the included studies; therefore, well-designed prospective research is highly suggested.

Level of Evidence:

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

The fate of positive intraoperative cultures following conversion total hip arthroplasty

INTRODUCTION

The objectives of this study are to report the rates of positive intraoperative cultures obtained during conversion total hip arthroplasty (THA) according to index surgery, and to describe the natural history of treatment for a consecutive series of patients with unexpected positive intraoperative cultures during conversion THA.

METHODS

We reviewed all patients at 2 institutions undergoing conversion THA from prior open reduction and internal fixation (ORIF) of acetabular and hip fractures or hemiarthroplasty for displaced femoral neck fractures from 2011 to 2018. Intraoperative cultures were taken in 105 patients. Positive intraoperative cultures during conversion were recorded and managed with an infectious diseases consult. The outcomes including PJI at 90 days and 1 year follow-up were documented.

RESULTS

Overall, 19 of 105 patients (18%) undergoing conversion THA had positive intraoperative cultures, with the highest rates in the hemiarthroplasty 7/16 (44%) and acetabular ORIF 9/48 (19%) groups. All 19 patients were initially treated conservatively: 8 received IV antibiotics, 10 received no additional therapy, and 1 received oral antibiotics. 4/9 acetabular fracture conversions developed PJI at 1 year, with 3 requiring multiple irrigation and debridement/polyethylene exchanges to control the infection while the 4th patient required 2-stage exchange. There were no 1-year PJI from any of the other index procedures after conversion. All 7 hemiarthroplasty patients with positive cultures were treated to resolution with 4-8 weeks IV antibiotics alone.

CONCLUSIONS

Patients undergoing conversion THA from prior hip or acetabular fracture have a high rate of positive intraoperative cultures. As such, all patients undergoing conversion THA from prior hip or acetabular fracture fixation should undergo thorough diagnostic workup prior to surgery, and have intraoperative cultures obtained during surgery if infection remains suspicious. Further work should be performed to develop MSIS criteria for preoperative management of patients undergoing conversion THA.

Utility of lavage in addition to native fluid collection during fluoroscopically guided joint aspiration in infection diagnosis

Image-guided prosthetic joint aspirations have been criticized in the literature as having poor sensitivity and specificity. Native fluid is typically analyzed for the presence of infection. Joint lavage during fluoroscopically guided aspiration of prosthetic joints is not routinely performed, and the lavage aspirate is not typically analyzed unless native fluid could not be aspirated for culture. This study aims to determine if concordance of culture results from native fluid and an additional joint lavage sample improves sensitivity and specificity in the diagnosis of prosthetic joint infection by fluoroscopically guided joint aspiration. A retrospective review of the fluoroscopically guided joint aspirations at our institution between December 2007 and December 2009 was performed. Data collected from the electronic medical record included culture results for both native fluid and lavage aspirate, histopathology results, final clinical diagnosis, as well as clinical/surgical management. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and likelihood ratio for infection were calculated for the following culture analysis scenarios: native fluid alone; lavage aspirate alone; native fluid; and lavage aspirate. Five hundred sixty-three aspirations, mostly prosthetic joints, were identified in the reviewed time period, of which 397 were sent for both native fluid and lavage aspirate analysis. Concordance between positive culture results from native fluid and joint lavage aspirate markedly increased the likelihood ratio for infection from 23.8 to 138.7 and improved specificity and PPV of fluoroscopically guided joint aspiration, with similar sensitivity and NPV to that of native fluid culture alone.

Prevalence and Outcomes of Unexpected Positive Intraoperative Cultures in Presumed Aseptic Revision Hip Arthroplasty

BACKGROUND

The prevalence and outcomes of unexpected positive cultures (UPCs) of specimens taken during presumed aseptic revision total hip arthroplasty (THA) are unclear. The purpose of this study was to determine the prevalence of UPC and infection-free implant survival in this patient population. Secondary aims included identifying factors associated with subsequent infection-related failure in patients with UPC.

METHODS

We reviewed all THA revisions (n = 2,288) performed at our institution from 2006 to 2019. Presumed aseptic revision THAs with intraoperative culture(s) were eligible (n = 1,196), and those with UPC were included in a Kaplan-Meier analysis to determine the infection-free implant survival and in Cox regression analysis to identify factors associated with infection-related failure.

RESULTS

UPC(s) were documented for 9.2% (110) of 1,196 aseptic THA revisions. The 2- and 5-year infection-free implant survival in the entire UPC cohort was 93.1% (95% confidence interval [CI] = 90.5% to 95.7%) and 86.8% (95% CI = 82.9% to 90.7%), respectively. The 2- and 5-year infection-free survival with failure due to infection with the same microorganism as identified in the UPC as the end point was 95.8% (95% CI = 93.7% to 97.9%) and 94.3% (95% CI = 91.7% to 96.9%), respectively. Subsequent infection-related failures caused by the same microorganism as identified in the UPC were more likely to occur after revisions with ≥2 UPCs than after those with 1 UPC (p = 0.024). Revision due to adverse metal reaction was a risk factor for subsequent infection-related failure (hazard ratio [HR] = 14.49, 95% CI = 2.69 to 78.04). Patients with a single UPC who were not treated with antibiotics had no subsequent periprosthetic joint infections (PJIs) caused by the same microorganism as identified in the UPC.

CONCLUSIONS

The prevalence of UPC was 9.2%, and the infection-free implant survival in patients with UPC is encouraging. Implant survival free of PJI caused by the same microorganism as identified in the UPC was excellent. Aseptic revision for adverse metal reaction was a risk factor for subsequent PJI in patients with UPC. No patient with a single UPC who was not treated with antibiotics developed PJI caused by the UPC-identified microorganism, suggesting that in the absence of other signs of infection a single UPC does not warrant antibiotic treatment.

LEVEL OF EVIDENCE

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

Periprosthetic joint infection in aseptic total hip arthroplasty revision

PURPOSE

There is no consensus regarding systematic screening for infection in aseptic revision total hip arthroplasty (THA). The rationale for systematic intra-operative samples is to increase the sensitivity of latent infections detection, which may require specific treatment. However, the incidence of occult infection in revision THAs is not precisely known. As such, the aim of the study was to evaluate the incidence of occult infection in presumed aseptic revision THAs and identify associated risk factors.

METHOD

Bacteriological samples from 523 aseptic THA revisions performed for five years were analyzed. Revisions performed for periprosthetic joint infection (PJI) or clinical suspicion of PJI were excluded. Microbiological cultures were performed using tissue samples in 505 cases (97%), synovial fluid in blood culture vials in 158 (30%), and in dry tubes in 263 (50%). Implants were sent for sonication in 12 cases (2.6%). The mean number of microbiological samples per patient was 3.6 (range, 1-15). Histology samples were collected for 300 patients (57%).

RESULTS

The incidence of occult infection was 7% (36 cases) and contamination 8% (42 cases). Among occult infections, the primary reasons for revision were dislocation (42%), aseptic loosening (25%), fracture (19%), and others (14%). The infection rate in the dislocation group was significantly higher than that of other reasons for revision (p < 0.001). Among the patients determined with PJI, the revision THA was performed less than a year after primary in 19 (53%).

CONCLUSION

The incidence of occult PJI justifies systematic intraoperative sampling. A short time between primary arthroplasty and revision or an early postoperative dislocation is a factor to suspect infections.

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.

Risk Factors for Positive Cultures in Presumed Aseptic Revision Spine Surgery

STUDY DESIGN

Retrospective case-control study.

OBJECTIVE

To report culturing patterns and results in the setting of presumed aseptic revision spinal surgery.

SUMMARY OF BACKGROUND DATA

The indications for obtaining cultures in revision spinal surgery remain unclear in the absence of a definitive diagnosis of infection. Culture results and risk factors for having positive cultures in this setting have not been previously studied.

METHODS

We retrospectively reviewed 595 consecutive revision spine surgeries performed by four senior spine surgeons between 2008 and 2013. Preoperative workup revealed the diagnosis of infection in 17 cases which were excluded from review. The remaining 578 presumed aseptic cases were included. Univariate and multivariate analyses were performed to identify variables associated with obtaining cultures and risk factors for positive cultures.

RESULTS

Cultures were obtained in 112 (19.4%) cases and were positive in 40.2%. Pseudarthrosis was the most common revision diagnosis when cultures were obtained (49.1%) and Propionibacterium acnes was the most common organism isolated from positive cultures (48.8%). Regarding culture results, multivariate analysis demonstrated that male sex (odds ratio [OR] = 3.4) and pseudarthrosis (OR = 4.1) were significantly associated with having positive cultures while fusion procedures (OR = 0.3) were negatively correlated, with area under the curve (AUC) 0.71.

CONCLUSION

Unexpected positive cultures occurred commonly and P. acnes was the predominant isolated organism. Male sex, pseudarthrosis, and non-fusion cases predicted positive cultures. Considering these results, we recommend cultures be obtained in revision cases for pseudarthrosis, even in the setting of negative infectious work-up preoperatively.

LEVEL OF EVIDENCE

4.

Sonication culture improves microbiological diagnosis of modular megaprostheses

Modular megaprostheses are known for high infection rates followed by high rates of revisions. Microbial biofilms growing adherently on prosthetic surfaces may inhibit the detection of the pathogens causing prosthetic joint infections. We sought to answer the following questions: Does sonication culture (SC) improve the microbiological diagnosis of periprosthetic infections of megaprostheses compared to conventional tissue culture (TC)? Which pathogens were detected on the surface of megaprostheses with either SC or TC and do the findings help to identify low-grade infections? Included were 31 patients with modular megaprostheses, whose implant had been explanted due to suspected joint infection or revision surgery. SCs were performed according to the protocol by Trampuz et al. The diagnosis of infection was evaluated according to the definition of the Musculoskeletal Infection Society. The sensitivity of SC was 91.3% compared to 52.2% for TC and the specificity was 100% for SC and TC (p = 0.004). Under preoperative antibiotic therapy, the sensitivity of SC was 83.3% while the sensitivity of TC was 50%. Without preoperative antibiotic therapy the sensitivity of SC was 100% compared to 54.5% for TC. In nine cases, SCs detected microorganisms, while TC was negative. Detected bacteria were Staphylococcus epidermidis in four, Micrococcus species in one, Finegoldia magna in one, Brevibacterium casei in one, Pseudomonas fluorescens in one, and Enterococcus faecium in one. SC is a reliable method for dislodging pathogens from orthopedic implants. The SC of modular megaprostheses showed significantly higher pathogen detection than the periprosthetic TC, especially for low virulence pathogens. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1383-1387, 2017.

Quality of Life in Sickle Cell Patients After Cementless Total Hip Arthroplasty

BACKGROUND

Osteonecrosis of femoral head is a serious relentlessly progressive and disabling complication in 20%-50% of sickle cell patients, majority of whom are in their second to third decades. High perioperative medical complications and short survivorship have historically discouraged arthroplasty surgeons in offering total hip arthroplasty to sickle cell patients in their 30s for the fear of inevitable technically demanding revision. In this retrospective study, the primary objective was to assess the impact of early intervention on quality of life (QOL) at midterm follow-up of mean 7.5 years using uncemented porous-coated total hip arthroplasty. The secondary objective of this study was the survival of the prostheses within the same follow-up period and discussion of surgical challenges faced in this cohort of patients.

METHODS

A total of 67 (84 hip arthroplasties) sickle cell patients with advance osteonecrosis of femoral head who underwent cementless porous-coated proximal fixation are included in this study. Modified Harris Hip Score, visual analog scale, and QOL assessment criteria are used to assess the outcome.

RESULT

Revision surgery was required in 7 patients for aseptic loosening and in 1 patient due to late infection. Visual analog scale improved from average 7 (6-9) to 3 (2-5). Mean Harris Hip Score improved from 46 (32-58) to 81 (74-86). QOL score rose from a mean of 3 (range 1-4) to 7 (range 6-9). In terms of gender, survival in males was 94.30%, whereas in females, it was 88.767%. Revision surgery was required in 7 patients due to aseptic loosening and in 1 patient due to late infection at 7 years.

CONCLUSION

We recommend early hip arthroplasty in sickle cell patients, if the hip has reached a stage of irreversible damage and patient's lifestyle is severely compromised to minimize chronic suffering and disability.

Recurrent Periprosthetic Joint Infection After Irrigation and Debridement With Component Retention Is Most Often Due to Identical Organisms

BACKGROUND

Irrigation and debridement with prosthetic retention (I&D) is an oft-utilized treatment option for PJI, despite its known limited success. While it is known that nearly half of all patients treated with I&D have recurrent infection, the organism persistence between infection events remains unreported. In addition, identifying those cases in which I&D routinely failed to eradicate the infection (not simply prevent recurrent infection) may allow improved patient selection for this less morbid procedure-a difficult task to date.

METHODS

Using an institutional database, 146 patients (153 joints) undergoing I&D between April 2000 and July 2013 were identified. There were 60 hips (40%). The overall success rate of I&D in this group was 52% (80/153). The failure group was limited to those patients with growth on culture at both initial failure and recurrent failure (46 cases). Analyses were performed to identify potential predictors of failed I&D and organism persistence in those cases.

RESULTS

In the study group, 83.7% (36/43) of cases failed with the same organism. Knees with failed I&D had an organism persistence of 92.3% (24/26) compared with 70.5% (12/17; P = .09) for the hip. Patients initially infected with Staphylococcus aureus (specifically methicillin-resistant [13/13]) had a higher risk of persistent PJI (96%; 24/25) compared to other organisms (66.7%; 12/18; P = .01).

CONCLUSION

I&D had a success rate of approximately 50% and typically failed due to organism persistence rather than a new infection. Given that persistent infection was most common in knees and S aureus, I&D should have a limited role in treating PJI, especially in these cases.

Occult Infection in Aseptic Joint Loosening and the Diagnostic Role of Implant Sonication

Our aim was to determine the incidence of occult infection and to examine the role of ultrasound sonication of the implants in cases of presumed aseptic loosening in a prospective trial. Joint swabs, aspirates, and deep tissue samples were obtained from around the prosthesis for routine microbiology. Each prosthesis was sonicated and the sonicate examined with Gram staining and extended cultures. There were 106 joints in the study of which 54 were revised for aseptic loosening and 52 were assigned to the control revision group. There were 9 positive cultures with 8/54 positive cultures in the aseptic loosening group and 1/52 in the control revision group (p = 0.017, associated OR 47.7). We found concordant results between sonication fluid culture and conventional samples in 5/9 cultures. Preoperative inflammatory markers were not prognostic for infection. Coagulase-negative Staphylococcus was the most commonly cultured organism (7/9). Previously unrecognised infection was present in 15% of patients undergoing revision for aseptic loosening. Ultrasound sonication of the removed prosthesis was less sensitive than conventional sampling techniques. We recommend routine intraoperative sampling for patients having revision for aseptic loosening, but we do not support the routine use of ultrasound sonication for its detection.

Comparison of procalcitonin and C-reactive protein for the diagnosis of periprosthetic joint infection before revision total hip arthroplasty

OBJECTIVE

To compare the clinical informative value of procalcitonin (PCT) and C-reactive protein (CRP) serum concentrations in the diagnosis of periprosthetic joint infection (PJI) before revision total hip arthroplasty (THA).

DESIGN AND METHODS

We conducted a prospective observational study of 71 consecutive patients (74 hips) undergoing revision THA. Procalcitonin and CRP serum concentrations and white blood cell (WBC) count were measured pre-operatively. Diagnostic accuracy was analyzed by the receiver-operating characteristic (ROC) curve and the area under the curve (AUC).

RESULTS

The PJI incidence was 35.2% in patients with revision THA. Procalcitonin and CRP serum concentrations and WBC count were statistically higher in the PJI cohort compared with the no PJI cohort (p<0.05). The AUCs for PCT, CRP, and WBC count were 0.851 (95% confidence interval [CI] 0.773-0.929), 0.830 (95% CI 0.751-0.910), and 0.633 (95% CI 0.518-0.747), respectively. Serum PCT and CRP showed a significantly higher diagnostic ability than WBC count (p<0.05). No significant difference was found between serum PCT and CRP (p=0.367).

CONCLUSION

Procalcitonin does not offer an advantage over CRP in diagnosing PJI. However, PCT and CRP proved to be more reliable than WBC count.

Unexpected positive intraoperative cultures in aseptic revision arthroplasty

Unexpected positive intraoperative cultures (UPIC) in presumed aseptic revision arthroplasty can be difficult to interpret. The purpose of this retrospective study was to compare the incidence of subsequent periprosthetic joint infection (PJI) in patients who received antibiotic therapy according to an institutional protocol with those who did not and whether they meet Musculoskeletal Infection Society (MSIS) criteria for PJI. In patients who were treated with antibiotic according to institutional criteria, the incidence of PJI after revision was higher in those who did not meet MSIS criteria (22%) than in those that met MSIS criteria (14%; P > 0.71). UPIC in aseptic revision arthroplasty are not uncommon. PJI cannot be excluded in patients that do not meet MSIS definition.

Optimal culture incubation time in orthopedic device-associated infections: a retrospective analysis of prolonged 14-day incubation

Accurate diagnosis of orthopedic device-associated infections can be challenging. Culture of tissue biopsy specimens is often considered the gold standard; however, there is currently no consensus on the ideal incubation time for specimens. The aim of our study was to assess the yield of a 14-day incubation protocol for tissue biopsy specimens from revision surgery (joint replacements and internal fixation devices) in a general orthopedic and trauma surgery setting. Medical records were reviewed retrospectively in order to identify cases of infection according to predefined diagnostic criteria. From August 2009 to March 2012, 499 tissue biopsy specimens were sampled from 117 cases. In 70 cases (59.8%), at least one sample showed microbiological growth. Among them, 58 cases (82.9%) were considered infections and 12 cases (17.1%) were classified as contaminations. The median time to positivity in the cases of infection was 1 day (range, 1 to 10 days), compared to 6 days (range, 1 to 11 days) in the cases of contamination (P < 0.001). Fifty-six (96.6%) of the infection cases were diagnosed within 7 days of incubation. In conclusion, the results of our study show that the incubation of tissue biopsy specimens beyond 7 days is not productive in a general orthopedic and trauma surgery setting. Prolonged 14-day incubation might be of interest in particular situations, however, in which the prevalence of slow-growing microorganisms and anaerobes is higher.

Multiple cultures and extended incubation for hip and knee arthroplasty revision: impact on clinical care

The impact on patient care of introducing a protocol of obtaining 5 or more intra-operative separate tissue biopsies that were cultured for 10 days was assessed for hip and knee arthroplasty revision. The charts of seventy-three patients undergoing 77 cases of revision arthroplasty were reviewed one year post-operatively. When compared to the prior standard of obtaining only one intra-operative culture, the protocol changed the microbiological diagnosis in 26/77 cases (34%, 95% Confidence Interval (CI): 23-45%) and antibiotic treatment in 23/77 cases (30%, 95% CI: 20-41%). In addition, the protocol had a predictive value of joint sterility in culture negative cases of 95% (95% CI: 85-99%). This data demonstrated the new protocol significantly changed patient care, and suggests that 1 or 2 cultures are insufficient. Adopting a similar protocol should be considered by surgeons and institutions as a new minimum standard for management of prosthetic joint infections.

Clinical meaning of unexpected positive cultures (UPC) in revision shoulder arthroplasty

PURPOSE

This study analyzed the prevalence and clinical meaning of unexpected positive cultures (UPCs) in revision shoulder arthroplasty for causes different than infection.

METHODS

Between 1976 and 2007, 107 consecutive patients with UPCs, no previous suspicion of infection, and fulfilling inclusion criteria were identified. Forty-five partial (PSA) and 62 total shoulder arthroplasties (TSA) with different preoperative diagnoses were reviewed. Cases were classified as true infections, possible infections, contaminants, and undetermined. Mean follow-up was 5.6 ± 5.3 years.

RESULTS

The prevalence of UPC was 15%. Male sex was a risk factor for UPC. Results of preoperative blood tests and intraoperative pathology were negative in 94 and 97 cases, respectively. Most prevalent bacteria were Propionibacterium acnes (n = 68) and Staphylococcus epidermidis (n = 21). Fifty-three patients received treatment with antibiotics and 54 did not. In 11 patients, a postoperative arthroplasty infection during follow-up was diagnosed by culture and was produced by the same microorganism as the one isolated on the UPC (true infection). Risk factors for true infection vs contamination included revision of a TSA vs a PSA and the number of previous surgeries. Antibiotic use and number of positive cultures did not influence the rate of true infections.

CONCLUSIONS

UPCs are a prevalent condition in revision shoulder arthroplasty for causes different than infection. In at least 25% of cases, UPC had no clinical relevance. In 10% of cases, a persistent infection was demonstrated.

Bacteriology of degenerated lumbar intervertebral disks

STUDY DESIGN

A prospective microbiological analysis of intervertebral disk material in surgically treated patients presenting lumbar disk degeneration.

OBJECTIVE

To determine the prevalence and species of bacteria in degenerated lumbar disks, their eventual role in the pathophysiology, and the possible influence of risk factors.

SUMMARY OF BACKGROUND DATA

Intervertebral disk degeneration results from biochemical, mechanical, genetic, and toxic factors. The hypothesis of low-grade infection has been raised but not elucidated to date.

METHODS

Eighty-three patients (34 males, 49 females, 41 y) were treated by lumbar disk replacement at L3-L4, L4-L5, or L5-S1. An intraoperative biopsy and microbiological culture were performed for each disk to determine if intradiskal bacteria were present. Magnetic resonance stages were Pfirrmann IV or V, with Modic I in 32, and Modic II in 25 cases. A preoperative discography was performed in 49 patients, 24 had previous nucleotomy.

RESULTS

Bacteria were found in 40 disks, 43 cultures were sterile. The following bacteria were evidenced: Propionibacterium acnes 18, coagulase-negative staphylococci 16, gram-negative bacilli 3, Micrococcus 3, Corynebacterium 3, others 5. Ten biopsies presented 2 different species. Multinucleated cells were evidenced histologically in 33% of positive biopsies. Bacteria were predominantly found in males (P=0.012). The mostly positive level was L4-L5 (P=0.075). There was no significant relationship between bacterial evidence and Modic sign. A preoperative discography or previous nucleotomy did not represent significant contamination sources. None of the patients presented infectious symptoms.

CONCLUSIONS

Although the hypothesis of biopsy contamination cannot be excluded, intradiskal bacteria might play a role in the pathophysiology of disk degeneration. However, the histologic presence of multinucleated cells may indicate an inflammatory process that could sustain the hypothesis of low-grade spondylodiscitis at 1 stage of the cascade of lumbar disk degeneration. These microbiological and histologic findings would need to be compared with nondegenerated disks.

LEVEL OF EVIDENCE

: Diagnostic level III.

Differential Bacterial Load on Components of Total Knee Prosthesis in Patients with Prosthetic Joint Infection

Purpose

The purpose of our study was to evaluate and quantify the bacterial adherence on different components of total knee prosthesis with the sonication culture method.

Methods

Explanted components of all patients with presumptive prosthetic or implant infection were treated by sonication separately in sterile containers to dislodge the adherent bacteria from the surfaces and cultured. The bacterial load of the different knee components (femur, tibia, PE-inlay and patella) was evaluated by counting of colony-forming units (CFU) dislodged from the components surfaces using the sonication culture method.

Results

Overall, 27 patients had positive sonication cultures of explanted total knee prostheses. Microorganisms were detected from 88 of 100 explanted components. Twenty femoral components were culture positive and 7 negative, 23 tibial components as well as 23 polyethylene (PE) platforms had positive microorganism detection from the surface. Staphylococcus epidermidis adhered to the highest number of components whereas Staphylococcus aureus yielded the highest load of CFU in the sonication cultures. Although not significant, PE-inlays and tibial components were most often affected. The highest CFU count was detected in polyethylene components.

Conclusion

The sonication culture method is a reliable method to detect bacteria from the components. Additionally, the results demonstrate that bacterial adherence is not affecting a single component of knee prosthesis only. Thus, in septic revision surgery partial prosthetic exchange or exchange of single polyethylene components alone may be not sufficient.

Management of periprosthetic joint infection: the current knowledge: AAOS exhibit selection

Periprosthetic joint infection continues to frustrate the medical community. Although the demand for total joint arthroplasty is increasing, the burden of such infections is increasing even more rapidly, and they pose a unique challenge because their accurate diagnosis and eradication can prove elusive. This review describes the current knowledge regarding diagnosis and treatment of periprosthetic joint infection. A number of tools are available to aid in establishing a diagnosis of periprosthetic joint infection. These include the erythrocyte sedimentation rate, serum C-reactive protein concentration, synovial white blood-cell count and differential, imaging studies, tissue specimen culturing, and histological analysis. Multiple definitions of periprosthetic joint infection have been proposed but there is no consensus. Tools under investigation to diagnose such infections include the C-reactive protein concentration in the joint fluid, point-of-care strip tests for the leukocyte esterase concentration in the joint fluid, and other molecular markers of periprosthetic joint infection. Treatment options include irrigation and debridement with prosthesis retention, one-stage prosthesis exchange, two-stage prosthesis exchange with intervening placement of an antibiotic-loaded spacer, and salvage treatments such as joint arthrodesis and amputation. Treatment selection is dependent on multiple factors including the timing of the symptom onset, patient health, the infecting organism, and a history of infection in the joint. Although prosthesis retention has the theoretical advantages of decreased morbidity and improved return to function, two-stage exchange provides a lower rate of recurrent infection. As the burden of periprosthetic joint infection increases, the orthopaedic and medical community should become more familiar with the disease. It is hoped that the tools currently under investigation will aid clinicians in diagnosing periprosthetic joint infection in an accurate and timely fashion to allow appropriate treatment. Given the current knowledge and planned future research, the medical community should be prepared to effectively manage this increasingly prevalent disease.

Validity of preoperative ultrasound-guided aspiration in the revision of hip prosthesis

Preoperative diagnosis of septic loosening hip prosthesis is often challenging. Culture test on joint samples obtained during revision surgery is the diagnostic gold standard while the role of preoperative hip aspiration is still controversial. The aims of this prospective randomized study were to compare the sensitivity, specificity and accuracy of preoperative ultrasound-guided and fluoroscopic-guided aspiration, and to identify associated laboratory parameters or scintigraphy that could help in predicting septic loosing hip prosthesis. Sixty patients affected by persistent pain after hip prosthesis randomly received fluoroscopic-guided or ultrasound-guided hip aspiration before revision surgery. The results of culture tests of joint fluid presurgically and at surgery were compared. In addition, associated blood inflammatory markers and scintigraphy were evaluated. Ultrasound-guided aspiration showed a better sensitivity (69% vs. 27%), specificity (94% vs. 75%) and accuracy (83% vs. 40%) than fluoroscopic-guided aspiration. The combination of ultrasound-guided aspiration and C-reactive protein represents the best model to predict septic loosening hip prosthesis preoperatively.

Molecular Diagnostics in Periprosthetic Joint Infection

Periprosthetic joint infection (PJI) is a significant and costly challenge to the orthopedic community. The lack of a gold standard for diagnosis remains the biggest obstacle in the detection and subsequent treatment of PJI. Molecular markers in the serum and joint fluid aspirate hold immense promise to enhance the development of a firm diagnostic criterion. The primary goal is one marker with high sensitivity and specificity. Here, we review our current research efforts in the field of molecular markers: C-reactive protein, erythrocyte sedimentation rate, white blood cells, and leukocyte esterase. Each marker has been studied to determine its sensitivity, specificity, and positive and negative predictive values in diagnosing PJI.

Definition of periprosthetic joint infection: is there a consensus?

BACKGROUND

The diagnosis of periprosthetic joint infection (PJI) continues to pose a challenge. While many diagnostic criteria have been proposed, a gold standard for diagnosis is lacking. Use of multiple diagnostic criteria within the joint arthroplasty community raises concerns in patient treatment and comparison of research pertaining to PJI.

QUESTIONS/PURPOSES

We (1) determined the variation in existing diagnostic criteria, (2) compared the existing criteria to a proposed new set of criteria that incorporates aspirate cell count analysis, and (3) investigated the variations between the existing criteria and the proposed criteria.

PATIENTS AND METHODS

We retrospectively identified 182 patients undergoing 192 revision knee arthroplasties who had a preoperative joint aspiration analysis at our institution between April 2002 and November 2009. We excluded 20 cases due to insufficient laboratory parameters, leaving 172 cases for analysis. We applied six previously published sets of diagnostic criteria for PJI to determine the variation in its incidence using each set of criteria. We then compared these diagnostic criteria to our proposed new criteria and investigated cases where disagreement occurred.

RESULTS

We identified 41 cases (24%) in which at least one established criteria set classified the case as infected while at least one other criteria set classified the case as uninfected. With our proposed criteria, the infected/uninfected ratio was 92/80. The proposed criteria had a large variance in sensitivity (54%-100%), specificity (39%-100%), and accuracy (53%-100%) when using each of the established criteria sets as the reference standard.

CONCLUSIONS

The discrepancy between definitions of infection complicates interpretation of the literature and the treatment of failed TKAs owing to PJI. Based on our findings, we suggest establishing a common set of diagnostic criteria utilizing aspirate analysis to improve the treatment of PJI and facilitate interpretation of the literature.

LEVEL OF EVIDENCE

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

Sonication cultures of explanted components as an add-on test to routinely conducted microbiological diagnostics improve pathogen detection

The purpose of this study was to improve the pathogen detection in prosthetic joint infections, particularly to evaluate the feasibility of the sonication culture method in the clinical routine. Explanted components of all patients with presumptive prosthetic or implant infection were sonicated separately in sterile containers to dislodge the adherent bacteria from the surfaces and cultured. The results of sonication culture were compared to the conventional tissue culture. We investigated 60 consecutive patients with loosening of the prostheses or implants Forty patients had septic and 20 aseptic loosening (24 knee prostheses, 21 hip prostheses, 6 mega-prostheses, 2 shoulder prostheses, 6 osteosynthesis, 1 spinal instrumentation). The sensitivity of sonication fluid culture was 83.3%, of single positive tissue culture was 72.2% and 61.1% when two or more cultures yielded the same microorganism. In patients receiving antibiotic therapy the sensitivity was 65.9%, 57.5%, and 42.5%, respectively. Pathogens detected in a single tissue culture as well as in sonication culture yielded a significantly higher rate of prosthetic infection than conventional tissue culture alone (p = 0.008), even in patients receiving continuous antibiotic therapy before explantation (p = 0.016). The sonication method represents an essential add-on in pathogen detection compared to conventional tissue culture.

Combining C-reactive protein and interleukin-6 may be useful to detect periprosthetic hip infection

BACKGROUND

The sensitivity and specificity to detect periprosthetic infection of the different methods have been questioned, and no single laboratory test accurately detects infection before revision arthroplasty.

QUESTIONS/PURPOSES

We asked whether preoperative C-reactive protein (CRP) and interleukin-6 (IL-6) could lead to similar sensitivity, specificity, and predictive values as our previous results obtained with intraoperative frozen section (FS) in revision total hip arthroplasty (THA).

METHODS

We prospectively followed 69 patients who had undergone revision THA for failure of a primary THA. The definitive diagnosis of an infection was determined on the basis of positive histopathologic evidence of infection or growth of bacteria on culture.

RESULTS

Eleven of the 69 hips were infected. The combination of an elevated CRP and IL-6 was correlated with deep infection in all the cases and showed a sensitivity of 0.57 (0.13-1.00), a specificity of 1.00 (0.99-1.00), a positive predictive value of 1.00 (0.87-1.00), and a negative predictive value of 0.94 (0.87-1.00). FS showed a sensitivity of 0.81 (0.54-1.00), a specificity of 0.98 (0.94-1.00), a positive predictive value of 0.90 (0.66-1.00), and a negative predictive value of 0.96 (0.91-1.00). Combining CRP and IL-6 provided similar sensitivity, specificity, and positive predictive values as the FSs.

CONCLUSIONS

Our data suggest the combination of CRP and IL-6 would be a useful serologic tool to complement others when diagnosing periprosthetic infection.

Non-purulent low-grade infection as cause of pain following shoulder surgery: preliminary results

Low-grade infection was systematically searched for in all revision shoulder surgeries by harvesting tissue samples. Ten consecutive patients were identified with a non-purulent low-grade infection of the shoulder. All of these patients suffered from pain and eight were stiff. Preoperative aspiration in eight patients yielded bacterial growth in only one case. Serum C-reactive protein levels were normal in seven out of 10 cases. Propionibacterium acnes was identified in seven, coagulase-negative Staphylococcus in two and Staphylococcus saccharolyticus in one case. The delay between harvesting the tissue samples and detection of bacterial growth averaged eight days (range, 2-17). After debridement and antibiotic treatment for a mean of 4.5 months, tissue samples were repeatedly harvested in nine patients due to persistent pain. The infection was microbiologically eradicated in six out of nine cases that had a repeated biopsy. However, nine out of 10 patients continued to suffer from moderate to severe pain. Low-grade infection of the shoulder can be a cause of persistent pain and stiffness. The results of antibiotic treatment are disappointing. Further studies are necessary to analyse this difficult pathology.

Perioperative testing for joint infection in patients undergoing revision total hip arthroplasty

BACKGROUND

While multiple tests are used to determine the presence of infection at the site of a total hip arthroplasty, few studies have applied a consistent algorithm to determine the utility of the various tests that are available. The purpose of the present study was to evaluate the utility of commonly available tests for determining the presence of periprosthetic infection in patients undergoing revision total hip arthroplasty.

METHODS

Two hundred and thirty-five consecutive total hip arthroplasties in 220 patients were evaluated by one of two surgeons using a consistent algorithm to identify infection and were treated with reoperation. Receiver-operating-characteristic curve analysis was used to determine the optimal cut-point values for the white blood-cell count and the percentage of polymorphonuclear cells of intraoperatively aspirated hip synovial fluid. Sensitivity, specificity, negative predictive value, positive predictive value, and accuracy were determined. Patients were considered to have an infection if two of three criteria were met; the three criteria were a positive intraoperative culture, gross purulence at the time of reoperation, and positive histopathological findings.

RESULTS

Thirty-four arthroplasties were excluded because of the presence of a draining sinus, incomplete data, or a preoperative diagnosis of inflammatory arthritis, leaving 201 total hip arthroplasties available for evaluation. Fifty-five hips were judged to be infected. No hip in a patient with a preoperative erythrocyte sedimentation rate of <30 mm/hr and a C-reactive protein level of <10 mg/dL was determined to be infected. Receiver-operating-characteristic curve analysis of the synovial fluid illustrated optimal cut-points to be >4200 white blood cells/mL for the white blood-cell count and >80% polymorphonuclear cells for the differential count. However, when combined with an elevated erythrocyte sedimentation rate and C-reactive protein level, the optimal cut-point for the synovial fluid cell count was >3000 white blood cells/mL, which yielded the highest combined sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the tests studied.

DISCUSSION

A synovial fluid cell count of >3000 white blood cells/mL was the most predictive perioperative testing modality in our study for determining the presence of periprosthetic infection when combined with an elevated preoperative erythrocyte sedimentation rate and C-reactive protein level in patients undergoing revision total hip arthroplasty.

Simulated joint infection assessment by rapid detection of live bacteria with real-time reverse transcription polymerase chain reaction

BACKGROUND

Although microbiological bacterial culture is currently considered the gold standard for diagnosis of septic arthritis, many studies have documented substantial false-negative and false-positive rates. The objective of this study was to determine whether real-time quantitative reverse transcription polymerase chain reaction can be used to detect bacterial messenger RNA (mRNA) in synovial fluid as a way to distinguish live and dead bacteria as an indicator of active infection.

METHODS

Synovial fluid samples were obtained from twelve consecutive patients who presented with knee pain and effusion but no evidence of infection. Following assurance of sterility with plate cultures, each sample was inoculated with clinically relevant bacteria and incubated for twenty-four hours to simulate septic arthritis. Bacterial viability and load were assessed with cultures. Selected samples were also treated with a single dose of a combination of two antibiotics, vancomycin and gentamicin, and sampled at several time points. Total RNA isolated from each sample was analyzed in triplicate with one-step real-time quantitative reverse transcription polymerase chain reaction to detect mRNA encoding for the genes groEL or femC. Controls included sterile, uninoculated samples and inoculated samples analyzed with quantitative polymerase chain reaction without reverse transcription. mRNA content was estimated on the basis of detection limits as a function of serial dilutions and was expressed as a function of colony number in bacterial cultures and RNA content as determined spectrophotometrically.

RESULTS

All synovial fluid samples that had been inoculated with one of the four bacterial species, and analyzed in triplicate, were identified (distinguished from aseptic synovial fluid) with real-time quantitative reverse transcription polymerase chain reaction; there were no false-negative results. All inoculated samples produced bacterial colonies on culture plates, while cultures of the aseptic samples were negative for growth. The detection limit of the one-step bacterial mRNA-based real-time quantitative reverse transcription polymerase chain reaction varied depending on the bacterial species. A time-dependent decrease in the concentration of detectable bacterial mRNA was seen after incubation of bacteria with antibiotics.

CONCLUSIONS

The direct quantification of the concentration of viable bacterial mRNA with real-time quantitative reverse transcription polymerase chain reaction allows identification of both culture-positive bacterial infection and so-called unculturable bacterial infection in a simulated septic arthritis model. In contrast to conventional polymerase chain reaction, real-time quantitative reverse transcription polymerase chain reaction minimizes false-positive detection of nonviable bacteria and thus provides relevant information on the success or failure of antibiotic therapy.

The fate of the unexpected positive intraoperative cultures after revision total knee arthroplasty

Of a consecutive series of 692 revision total knees at 3 centers, intraoperative cultures were unexpectedly found to be positive in 41 cases (5.9%). Of the 41, 29 (71%) cases had a single positive intraoperative culture and were determined to be a probable false positive based on absence of any other evidence of infection, of which 5 were treated with extended course of intravenous antibiotics after hospital discharge and the remaining 24 received no further treatment. None of these 24 patients manifested any sign of infection at follow-up, averaging 46 months (range, 24-74 months). Twelve patients were determined to have probable type 1 periprosthetic infection, 11 of which were treated with a course of antibiotics. Two of these patients became reinfected within a year. A single positive intraoperative culture after revision total knee arthroplasty does not mandate further treatment in the absence of any other signs of infection.

Identification of orthopaedic infections using broad-range polymerase chain reaction and reverse line blot hybridization

BACKGROUND

Culture remains the gold standard in the diagnosis of bacterial infection, but molecular biological techniques have yielded promising results. In this study, we validated a combined polymerase chain reaction and reverse line blot hybridization protocol for identifying musculoskeletal infections.

METHODS

Samples were obtained from seventy-six patients undergoing orthopaedic surgery for various aseptic and septic indications. The diagnosis of infection was based on a review of all available clinical and culture data. In addition to routine culture for aerobic and anaerobic growth, samples were analyzed with a broad-range 16S rRNA polymerase chain reaction and subsequent reverse line blot hybridization with use of twenty-eight group, genus, and species-specific oligonucleotide probes.

RESULTS

An infection was diagnosed on the basis of patient data in thirty-one patients. All but one of the patients with a clinical diagnosis of infection had a positive result of the polymerase chain reaction-reverse line blot hybridization. Five of the forty-five patients in whom an infection was not suspected on the basis of patient data had at least one positive result of the polymerase chain reaction-reverse line blot hybridization. Cultures demonstrated microorganisms in twenty-five patients with an infection and in two patients in whom an infection was not suspected on the basis of the patient data. Staphylococcus aureus was the most common organism grown on culture. The species identified by the polymerase chain reaction-reverse line blot hybridization was in full accordance with that grown on culture in all but one patient.

CONCLUSIONS

Polymerase chain reaction-reverse line blot hybridization performed well in detecting and identifying the various bacterial species and was more sensitive than routine culture. It identified Staphylococcus aureus as the most frequently found microorganism. Five patients in whom an infection was not suspected on the basis of the patient data had a positive result of the polymerase chain reaction, which may have been caused by contamination of the samples. However, three of these patients had aseptic loosening of a total hip prosthesis, suggesting the presence of a low-grade bacterial infection that remained undetected by the culture but was detected by the polymerase chain reaction-reverse line blot hybridization.

LEVEL OF EVIDENCE

Diagnostic Level III.

Cultures of sternal wound and mediastinum taken at the end of heart surgery do not predict postsurgical mediastinitis

The aim of the study was to assess of the role of intraoperative cultures taken at the end of major heart surgery (MHS) in the prediction of postoperative mediastinitis (PM) in patients undergoing MHS over a 6-month period in a tertiary university hospital. Just before wound closure, a sample of the sternal border was taken, swabbing back and forth the sternal border and the subcutaneous tissues. A second sample was taken after irrigation of the deep mediastinal structures with 10 mL of Ringer lactate. Swabs were processed semiquantitatively and the mediastinal fluid with a quantitative technique. The observation of one or more colonies per plate was considered a positive culture. Cultures obtained at the end of 229 surgical interventions (227 patients) were positive with the semiquantitative or with the quantitative procedures in 31.0% (95% confidence interval [CI], 25.1-37.4%) and 34.5% (95% CI, 28.4-41.0%) of the times, respectively (P = NS). The number of microorganisms isolated in the wound swab or mediastinal fluid was 91 and 110, respectively. Of the 227 patients, 7 developed an episode of PM (3.1%; 95% CI, 1.2-6.2%) after a median time of 11 days (range, 5-19 days). The microorganisms causing the 7 cases of mediastinitis were not isolated in the intraoperative cultures in any of the cases. The value of intraoperative cultures as a test for prediction of PM depending on the breakpoint chosen were as follows: sensitivity (0%), specificity (66.2-97.3%), and positive (0%) and negative predictive values (96.8-98.0%). We recommend against surveillance cultures taken intraoperatively in patients undergoing MHS.

Improved aero-anaerobe recovery from infected prosthetic joint samples taken from 72 patients and collected intraoperatively in Rosenow's broth

INTRODUCTION

Recovery of the bacteria responsible for prosthetic joint infections is a major problem, which is due in part to the alteration of their ability to grow by storage during transportation to the laboratory.

METHODS

In this prospective study, we assessed the benefit of inoculating an enriched liquid medium (Rosenow's broth) with intraoperative samples from 72 patients with prosthetic joint revision due to infection. We compared the results of culture of specimens collected in a standard receptacle with the results for specimens collected in Rosenow's broth.

RESULTS AND INTERPRETATION

144 samples were taken by each of the 2 collection methods for subsequent culture. Concordance between standard and Rosenow samples was observed for 52 of the 58 strains cultured on agar and for 42 of the 97 strains (p < 0.001) which grew only in liquid medium. Infection would not have been diagnosed in 26 patients (almost one-third of all patients) without combining sample collection in Rosenow's broth with standard collection. The bacteria that were not recovered from standard samples but which were recovered from those collected in Rosenow's broth included not only strict anaerobes, in particular Propionibacterium acnes, but also coagulase-negative staphylococci and streptococci.

[Improving microbiological diagnostics in septic orthopaedic surgery. Comparative study of patients receiving systemic antibiotic therapy]

MATERIAL AND METHODS

This prospective study included 63 patients with confirmed infections of soft tissue, joints, bones or implants. During 110 surgical interventions, 124 swab and deep tissue sample pairs were taken and analysed microbiologically using standard procedures.

RESULTS

In 40 patients who had not received prior antibiotic treatment, 57 sample pairs (swabs/tissue) were taken. In 70%, growth of microorganisms could be observed in both swabs and tissue samples. Growth in tissue sample only was observed in 14% and in 14% no growth could be detected. In 67 sample pairs taken from 23 patients who had received systemic antimicrobial treatment prior to surgery, microbial growth in both specimens was detected in 40%. Growth in tissue sample only was observed in 22% and 34% of the samples remained without detectable growth. The overall sensitivity of the tissue samples (70%) was significantly higher than in swab samples (44%) for the pretreated group.

CONCLUSION

The use of intraoperative tissue samples for microbiological diagnostics in septic orthopaedic surgery must be considered a "gold standard". The higher sensitivity of intraoperative tissue samples is particularly important in patients receiving systemic antibiotic therapy prior to surgical interventions.

Propionibacterium acnes wound contamination at the time of spinal surgery

Bacteria of the normal skin microbiota such as Propionibacterium acnes and coagulase-negative staphylococci often are dismissed as contaminants when detected in clinical samples. Propionibacterium acnes is described as a cause of spinal infection and more recently has been linked to sciatica. To date no researchers formally have examined the incidence of bacterial wound contamination during spinal surgery. Surgical specimens were removed from 79 patients having spinal surgery for analysis using agar culture detection, broth enrichment, and immunofluorescence microscopy. Bacteria were identified in 29.1% of skin samples, 21.5% of tissue samples and 16.5% of washings retrieved from operative wounds. Propionibacterium acnes was identified more frequently than Staphylococcus spp in each of the three sample types. Bacteria were detected using enrichment in 9 (11%) patients and using fluorescence microscopy in 15 (19%). The results of immunofluorescence microscopy suggest that Propionibacterium acnes detected in wounds originates from patient skin. Bacteria from contaminated wounds appeared as single cells using fluorescence microscopy; however previous work shows that bacteria from infected hip prosthesis are observed as large aggregates. Therefore, it is suggested that immunofluorescence microscopy is a useful tool to help discriminate between surgical contamination and infection.

LEVEL OF EVIDENCE

Diagnostic study, Level I (prospective study). See the Guidelines for Authors for a complete description of levels of evidence.

Molecular diagnosis of prosthetic joint infection. A review of evidence

Prosthetic joint infection (PJI) diagnosis includes several classes of verification. Among them, only a few have a stronger independent value, namely intraarticular purulence and communicating fistulas. Other diagnostic methods require careful test combinations, analysis, and interpretation. Molecular based techniques using the polymerase chain reaction (PCR) seem to be a promising PJI diagnostic modality due to its excellent sensitivity, specificity, positive predictive value, and speed. Most of the recent reviewers are in agreement that molecular diagnosis has enough potential for future application in orthopaedics even if there are only a few heterogeneous studies fully supporting this concept. Conversely, at least one study has been published with significantly worse results (sensitivity and specificity less than 0.75). The lack of supporting evidence in the published studies may be closely related to varying PCR laboratory procedures, inappropriate reference standards, and other methodological shortcomings among research centers. It is not yet justifiable to firmly include molecular methods into the present PJI diagnostic schemes. The orthopaedic community must await the results of well-organized ongoing studies before considering inclusion of molecular diagnostics as a PJI diagnostic method. The aim of this paper was to make a survey of current PJI molecular diagnostic techniques in orthopaedics.

Periprosthetic sepsis

The diagnosis of septic implant failure can be difficult to make, yet is imperative for optimal patient outcomes in revision total hip arthroplasty. In most cases, a thorough history and physical examination combined with preoperative laboratory tests and an intraoperative frozen section are sufficient to differentiate septic from aseptic failure. If preoperative laboratory test values are elevated, preoperative aspiration of the hip can be used in selected patients to confirm or exclude the diagnosis of infection. Nuclear medicine studies comprise a second-line investigation to evaluate patients with a painful total hip arthroplasty in whom revision surgery otherwise is not indicated. Intraoperative tissue appearance in combination with intraoperative Gram stains are unreliable for detecting periprosthetic sepsis, and neither is adequate when considered alone for ruling out infection at the time of revision total hip arthroplasty. It is imperative that the surgeon doing revision total hip arthroplasty thoroughly understands the relative utility of preoperative and intraoperative tests used to diagnose periprosthetic sepsis.

Role of core biopsy in diagnosing infection before revision hip arthroplasty

A prerevision core biopsy from a failed hip joint was performed in 41 hips (38 patients) with a high index of suspicion for sepsis to determine its efficacy in diagnosing sepsis. Seven hips were known septic failures, and core biopsy was undertaken to confirm resolution of sepsis. Forty hips were revised, whereas 1 hip had excision of heterotopic bone. Cultures and permanent histologic sections were obtained during subsequent surgeries, and findings were compared with the results of core biopsy. The commonest organisms isolated were coagulase-negative staphylococci and Propionibacterium acne. In patients without a history of sepsis, core biopsy diagnosed infection with sensitivity of 80%, specificity of 100%, accuracy of 97%, and positive predictive value of 100% using histologic evidence of sepsis at revision as the standard. Core biopsy, however, had low sensitivity and accuracy in establishing resolution of infection in patients with a history of septic failure. Cultures from the aspirate had 44% sensitivity and positive predictive value of 57%. Core biopsy is useful for investigating failed arthroplasties with suspected sepsis. It has advantages of hip aspiration and allows examination of periprosthetic tissue histology. Its role in diagnosing resolution of infection in previously septic failures, however, is limited.

Simultaneous bilateral total hip arthroplasty in sickle cell disease

Simultaneous bilateral uncemented total hip arthroplasty for avascular necrosis of the femoral head resulting from sickle cell disease was performed in 18 consecutive patients (36 hips). The patients were followed 2 to 10 years (mean, 5.7 years). All patients showed improvement in postoperative hip scores compared with preoperative scores for pain, range of motion, and function. There were 2 immediate postoperative complications related to sickling of red blood cells. One intraoperative fracture of the proximal femur occurred. There was 1 superficial and 1 deep infection. There was no femoral stem loosening, but 1 protrusio acetabuli occurred. One acetabular cup was revised for instability. Heterotopic ossification developed in 2 patients. Simultaneous bilateral total hip arthroplasty in sickle cell disease is a good option in a select group of patients with adequate hydration and ventilation in the perioperative and postoperative periods.

Efficacy of combined technetium-99m sulfur colloid/indium-111 leukocyte scans to detect infected total hip and knee arthroplasties

The reliability of combined indium-111 leukocyte/technetium-99m sulfur colloid scans, with and without the addition of blood pooling and blood flow studies, in the diagnosis of infected total joint arthroplasty was investigated. Both scans were performed on 58 patients before reoperation of total hip or knee arthroplasty in the period 1996-1999. Results for imaging alone included 100% specificity, 46% sensitivity, 100% positive predictive value, 84% negative predictive value, and 88% accuracy. Inclusion of blood pooling and flow phase data improved results to 66% sensitivity, 89% negative predictive value, and 90% accuracy, with reductions in specificity (98%) and positive predictive value (91%). Routine use of these radionuclide scans is not supported by these data.

The predictive value of indium-111 leukocyte scans in the diagnosis of infected total hip, knee, or resection arthroplasties

To evaluate the usefulness of the indium-111 scan in detecting actually or potentially infected total hip, knee, and resection arthroplasties, 153 scans were performed on 143 patients who underwent reoperation for a loose or painful total joint arthroplasty or a resection arthroplasty between 1990 and 1996. Scans were interpreted as infected, not infected, or equivocal by an experienced nuclear medicine radiologist. Patients were considered to be infected if they met any 2 of the following criteria: i) positive intraoperative cultures, ii) final permanent histologic section indicating acute inflammation, and iii) intraoperative findings of gross purulence within the joint. Twenty-six patients (17%) met the infection criteria at the time of reoperation. Indium scans were found to have a 77% sensitivity, 86% specificity, 54% and 95% positive and negative predictive values, and 84% accuracy for the prediction of infection. Of 6 equivocal scans, none were infected. The results of this study suggest limited indications for the use of the indium-111 scan in the evaluation of painful hip, knee, or resection arthroplasties. A negative indium scan may be helpful in suggesting the absence of infection in cases in which the diagnosis is not otherwise evident.

Prospective analysis of preoperative and intraoperative investigations for the diagnosis of infection at the sites of two hundred and two revision total hip arthroplasties

BACKGROUND

Total hip arthroplasty is a commonly performed procedure in the United States and Canada that is associated with a definite risk of postoperative infection. Moreover, diagnosing an infection after total hip arthroplasty can present a challenge as there are no preoperative tests that are consistently sensitive and specific for infection in patients who need a revision arthroplasty. The present prospective study was performed to evaluate a variety of investigations for the diagnosis of infection at the site of a previous arthroplasty in order to determine if any combination of diagnostic studies could be used to determine which patients are at risk for a postoperative wound infection.

METHODS

We prospectively analyzed the preoperative and intraoperative investigations used for the diagnosis of infection in 178 patients who had a total of 202 revision hip replacements. Clinical data were collected preoperatively. Investigations to determine the presence or absence of infection included a white blood-cell count, measurement of the erythrocyte sedimentation rate, measurement of the level of C-reactive protein, preoperative aspiration of the joint, intraoperative gram-staining and culture of periprosthetic tissue, a white blood-cell count in synovial fluid, and examination of intraoperative frozen sections. Frozen sections were analyzed in a blinded fashion without knowledge of clinical or laboratory data. Patients receiving antibiotics at the time of aspiration or collection of specimens for intraoperative culture were excluded from the analysis of those investigations, regardless of the results of the cultures. A positive result (suggestive of infection) was clearly defined for each of the investigations.

RESULTS

Thirty-five hips (17 percent) were determined to be infected on the basis of clinical findings and positive results, according to the defined criteria, of investigations. With inflammatory conditions excluded, the sensitivity, specificity, positive predictive value, and negative predictive value were 0.82, 0.85, 0.58, and 0.95, respectively, for the erythrocyte sedimentation rate and 0.96, 0.92, 0.74, and 0.99, respectively, for the level of C-reactive protein. All patients who had a periprosthetic infection had an elevated erythrocyte sedimentation rate or level of C-reactive protein, but not always both. When patients who were receiving antibiotics were excluded, the results of aspiration of the joint were 0.86 for sensitivity, 0.94 for specificity, 0.67 for the positive predictive value, and 0.98 for the negative predictive value. Intraoperative studies revealed sensitivities, specificities, positive predictive values, and negative predictive values of 0.19, 0.98, 0.63, and 0.89, respectively, for gram-staining of specimens of the most inflamed-appearing tissue; 0.36, 0.99, 0.91, and 0.90, respectively, for the white bloodcell count in synovial fluid; and 0.89, 0.85, 0.52, and 0.98, respectively, for a neutrophil count in synovial fluid of more than 80 percent. The sensitivity, specificity, positive predictive value, and negative predictive value were 0.80, 0.94, 0.74, and 0.96, respectively, for the frozen sections and 0.94, 0.97, 0.77, and 0.99, respectively, for the intraoperative cultures.

CONCLUSIONS

The combination of a normal erythrocyte sedimentation rate and C-reactive protein level is reliable for predicting the absence of infection. Aspiration should be used when the erythrocyte sedimentation rate or the C-reactive protein level is elevated or when a clinical suspicion of infection remains. We found the gram stain to be unreliable. Examination of intraoperative frozen sections is useful in equivocal cases or when hematological markers may be falsely elevated because of an inflammatory or other condition.