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

Classic Markers for Infection Perform Poorly in Predicting Residual Infection Prior to Reimplantation

Two-stage exchange arthroplasty remains the treatment of choice for chronic periprosthetic joint infections. This retrospective study conducted between 2009 and 2015 examined the diagnostic value of biomarkers for residual infection between stages. The biomarkers evaluated included C-reactive protein prior to reimplantation, preimplantation synovial fluid white blood cell count and percent neutrophils, and the intraoperative histologic synovial white blood cell count per high-power field (×400) on permanent sections. Residual infection was defined as either positive cultures (more than 1) at second stage, any further surgery (eg, amputation, arthrodesis, or another 2-stage revision), or the need for infection suppression with antibiotics. Sensitivity, specificity, positive and negative predictive values, and likelihood ratios were calculated accordingly. A total of 182 two-stage exchange operations that included 109 (59.9%) prosthetic hips and 73 (40.1%) prosthetic knees met the inclusion criteria. Residual infection was present in 38 (20.9%) of the procedures. The area under the curve-receiver operating characteristic values were 0.677 for C-reactive protein (P=.002), 0.506 for aspiration white blood cell count (P=.944), 0.623 for aspiration percent neutrophils (P=.200), and 0.524 for white blood cell count per high-power field (P=.801). Positive and negative predictive values were poor and ranged between 26% and 57% and 78% and 85%, respectively. Analyses using specific combinations of biomarkers did not significantly improve predictive values. This study showed that classic markers perform poorly in identifying residual infection prior to second-stage revision. Further research is necessary to evaluate the diagnostic utility of other, more recently introduced biomarkers to determine whether infection has been eradicated between stages. [Orthopedics. 2019; 42(1):34-40.].

Normal CRP and WBC values in total hip arthroplasty (THA) with signs of loosening. Do we need a joint aspiration?

PURPOSE

Overall Total hip arthroplasty (THA) is a very successful procedure. However, in case of complication dedicated management is required. Two major complications of THA failures are aseptic loosening (AL) and periprosthetic joint infection (PJI). The primary hypothesis of this study was that joint aspirations in patients with signs of loosening after THA are capable to detect PJI in suspected AL with negative serologic testing.

METHODS

In this study a total of 108 symptomatic patients with radiographic signs of prosthetic loosening and hip pain in THA were included. Based on a standardized algorithm all patients underwent serological testing followed by joint aspiration preoperatively. Intraoperatively harvested samples were subjected to microbiological testing and served as the gold standard in differential diagnosis. Demographics, as well as the results of serologic and microbiological testing were collected from the medical records.

RESULTS

Of the included patients 85 were finally diagnosed with an AL and 23 with PJI. Within the patients with PJI 13 (56%) patients demonstrated elevated CRP and WBC counts, as well as positive synovial cultures after joint aspiration. In ten patients (44%) diagnosed with PJI neither CRP nor WBC were abnormal.

CONCLUSION

The diagnosis of PJI can be difficult in THA with radiographic signs of loosening. Clinical features including pain, fever, and local sings of infection are uncommon especially a long period after index operation. First-line screening testing relies on serological evaluation of CRP and WBC. However, normal CRP and WBC values cannot rule out a PJI. These cases can be detected by joint aspiration and synovial cultures reliably.

Sonication versus Tissue Sampling for Diagnosis of Prosthetic Joint and Other Orthopedic Device-Related Infections

Current guidelines recommend collection of multiple tissue samples for diagnosis of prosthetic joint infections (PJI). Sonication of explanted devices has been proposed as a potentially simpler alternative; however, reported microbiological yield varies. We evaluated sonication for diagnosis of PJI and other orthopedic device-related infections (DRI) at the Oxford Bone Infection Unit between October 2012 and August 2016. We compared the performance of paired tissue and sonication cultures against a "gold standard" of published clinical and composite clinical and microbiological definitions of infection. We analyzed explanted devices and a median of five tissue specimens from 505 procedures. Among clinically infected cases the sensitivity of tissue and sonication culture was 69% (95% confidence interval, 63 to 75) and 57% (50 to 63), respectively (P < 0.0001). Tissue culture was more sensitive than sonication for both PJI and other DRI, irrespective of the infection definition used. Tissue culture yield was higher for all subgroups except less virulent infections, among which tissue and sonication culture yield were similar. The combined sensitivity of tissue and sonication culture was 76% (70 to 81) and increased with the number of tissue specimens obtained. Tissue culture specificity was 97% (94 to 99), compared with 94% (90 to 97) for sonication (P = 0.052) and 93% (89 to 96) for the two methods combined. Tissue culture is more sensitive and may be more specific than sonication for diagnosis of orthopedic DRI in our setting. Variable methodology and case mix may explain reported differences between centers in the relative yield of tissue and sonication culture. Culture yield was highest for both methods combined.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

LEVEL OF EVIDENCE

Diagnostic Level II.

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

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

Periprosthetic Joint Infection in Patients with Inflammatory Joint Disease: Prevention and Diagnosis

PURPOSE OF REVIEW

Periprosthetic joint infection (PJI) is a devastating complication that can occur following total joint arthroplasty (TJA), causing significant morbidity and often requiring revision surgery. This goal of this manuscript is to review the current evidence for the prevention and diagnosis of PJI in patients with inflammatory arthritis.

RECENT FINDINGS

Patients with inflammatory arthritis have a higher risk of PJI after TJA; however, there are several preventive, diagnostic, and therapeutic measures that can be optimized to lower the burden of PJI in this population. This manuscript will review the current evidence and clinical practice recommendations that support specific features of preoperative evaluation, perioperative medication management, and surgical planning in inflammatory arthritis patients undergoing TJA. Evidence and recommendations for the diagnosis of PJI in this patient population will also be reviewed. Despite increased research efforts directed towards PJI, specific approaches directed at the inflammatory arthritis patient population remain surprisingly limited. Optimization strategies such as adequately managing disease-modifying medications, treating preoperative anemia, encouraging smoking cessation, and improving weight management are strongly encouraged before entering the perioperative period. If PJI does occur in the inflammatory arthritis patient, establishing the diagnosis is challenging, since guidelines were created from investigations of PJI in primarily patients without inflammatory arthritis. Future prospective research is required to better guide clinicians in preventing and diagnosing PJI in inflammatory arthritis patients undergoing TJA.

Culture of Bone Biopsy Specimens Overestimates Rate of Residual Osteomyelitis After Toe or Forefoot Amputation

BACKGROUND

Guidelines recommend both histological analysis and culture for definite diagnosis of osteomyelitis. It is not clear if histological and culture criteria can be used interchangeably in the clinical scenario of toe amputation. We therefore prospectively compared the results of intraoperative culture and those of histological examination in this setting.

METHODS

Consecutive patients requiring toe or forefoot amputation at the University Hospital Basel during a 2-year period were included in the study. Biopsy specimens from the residual bone were cultured according to microbiological standards. Histological analysis was performed using standardized criteria for osteomyelitis. Clinical outcomes were assessed retrospectively via chart review.

RESULTS

Of 51 patients included in the study, 33 (65%) had a positive culture of residual bone and 14 (27%) showed histological signs of osteomyelitis. A negative histological result but a positive culture was found for 21 (41%) of the patients, suggesting that culture has a high false-positive rate if histological analysis is used as the reference to rule out osteomyelitis. The recommended criteria of both positive histological findings and positive culture were fulfilled by 12 (24%) of the 51 patients.

CONCLUSIONS

Positive cultures of residual bone after forefoot or toe amputation overestimate the true rate of osteomyelitis as defined by histological analysis, presumably because of contamination from soft tissue at the time of surgery. Additional studies are needed to evaluate the indications for, and the duration of, antibiotic treatment according to these findings.

CLINICAL RELEVANCE

Our results cast doubt on the strategy of relying solely on culture of bone biopsy specimens when deciding whether antibiotic treatment for osteomyelitis is necessary after toe or forefoot amputation.

Management of Periprosthetic Joint Infection

Periprosthetic joint infection (PJI) is a serious complication after arthroplasty, which is associated with pain, prolonged hospital stay, multiple surgeries, functional incapacitation, and even mortality. Using scientific and efficient management protocol including modern diagnosis and treatment of PJI and eradication of infection is possible in a high percentage of affected patients. In this article, we review the current knowledge in epidemiology, classification, pathogenesis, diagnosis and treatment of PJI.

Histopathological Diagnosis of Prosthetic Joint Infection: Does a Threshold of 23 Neutrophils Do Better than Classification of the Periprosthetic Membrane in a Prospective Multicenter Study?

No gold standard exists for histopathological diagnosis of a prosthetic joint infection (PJI). The historical criterion considers the presence of neutrophil infiltration upon examination of periprosthetic tissue. Morawietz et al. proposed a classification of periprosthetic membranes (Morawietz et al., Clin Pathol 59:591-597, 2006, https://doi.org/10.1136/jcp.2005.027458) and a more recently described classification with a new cutoff value of 23 neutrophils in 10 high-power fields (Morawietz et al., Histopathology 54:847-853, 2009. https://doi.org/10.1111/j.1365-2559.2009.03313.x). We performed a multicenter prospective study, which compared both methods for the diagnosis of PJI. All suspicions of PJI (n = 264) between December 2010 and March 2012 in seven centers were prospectively included. Five perioperative specimens were collected per patient for cultures, and one was collected for histology. Diagnosis of PJI was made according to the Infectious Diseases Society of America (IDSA) guidelines. Histopathological analysis classified the patients according to the threshold of 23 neutrophils and according to the classification of Morawietz. Performances of both methods were compared by using clinical and/or bacteriological criteria as the gold standard. Among 264 patients with suspected PJI, a diagnosis of infection was confirmed in 215 and unconfirmed in 49 patients. Histopathological analysis was available for 150 confirmed PJI and 40 unconfirmed PJI cases. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 78.7%, 90.0%, 96.7%, 52.9%, and 81.1%, respectively, for the Morawietz classification, and 82.0%, 90.0%, 96.9%, 57.1%, and 83.7%, respectively, for the 23-neutrophil threshold. The new algorithm using a threshold of 23 neutrophils can be proposed as a new gold standard for the histopathological diagnosis of PJI.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

Do Culture-Negative Periprosthetic Joint Infections Have a Worse Outcome Than Culture-Positive Periprosthetic Joint Infections? A Systematic Review and Meta-Analysis

BACKGROUND

Culture-negative periprosthetic joint infections (CN PJI) have not been well studied, and due to the lack of consensus on PJI, especially with culture-negative infections, there are considerable uncertainties. Due to the challenging clinical issue of CN PJI the aim of this systematic review is to describe incidence, diagnosis, and treatment outcomes based on the current literature on CN PJI.

HYPOTHESIS

The review is designed to assess the formal hypothesis that CN PJI of the hip and knee have a poorer outcome when compared with culture-positive ones.

STUDY DESIGN

It is systematic review with level of evidence 3.

METHODS

EMBASE, MEDLINE, and the Cochrane Library were searched electronically in January 2018. All studies regarding CN PJI of the hip or knee published in English or German with a minimum of 10 patients were included. Afterwards, the authors performed a descriptive analysis of diagnosis and treatment outcome.

RESULT

Eight studies were identified that met the inclusion criteria. The incidence of CN PJI in the hip or knee ranged from 7% to 42 %. The included studies were pooled to give an overall incidence rate estimate of 11 % [95% confidence interval (CI): 10-12] based on a random-effects model. The most common surgical intervention was the two-stage revision of prosthesis with 283 patients. Postoperatively, the majority of patients received vancomycin as the antibiotic treatment, alone or in combination with other antibiotics. The rate of succesfully treated infections varied from 85% to 95 % in all included studies. The two-stage exchange arthroplasty had the best outcome, based on the infection-free survival rate of 95%, five years after treatment.

CONCLUSIONS

We conclude that CN PJI have the same or even better results than culture-positive infections. Nonetheless, a standardized diagnostic protocol and evidence-based treatment strategies for CN PJI should be implemented for further studies.

Joint aspiration, including culture of reaspirated saline after a 'dry tap', is sensitive and specific for the diagnosis of hip and knee prosthetic joint infection

Aims

The aim of this study was to establish the diagnostic accuracy of culture of joint aspirate with and without saline injection-reaspiration.

Patients and Methods

This is a retrospective analysis of 580 hip and knee aspirations in patients who were deemed to have a moderate to high risk of infection, and who subsequently proceeded to revision arthroplasty over a period of 12 years. It was carried out at a large quaternary referral centre where preoperative aspiration is routine.

Results

Fluid was aspirated primarily in 313 (54%) cases and after saline injection-reaspiration of a 'dry tap' in 267 (46%) cases. Overall sensitivity and specificity of the diagnostic aspirate were 84% (78% to 89%) and 85% (81% to 88%), respectively. Sensitivity and specificity of saline injection-reaspiration after 'dry tap' were 87% (79% to 92%) and 79% (72% to 84%) compared with 81% (71% to 88%) and 90% (85% to 93%) for direct aspiration.

Conclusion

Preoperative joint aspiration and culture is a sensitive and specific test for the confirmation of diagnosis in patients at a moderate to high risk of prosthetic joint infection. Culture of saline injection-reaspiration also provides accurate diagnostic information in the event of a 'dry tap'. Both methods allow susceptibility testing of relevant organisms and are therefore able to guide perioperative antibiotic therapy. Cite this article: Bone Joint J 2018;100-B:749-54.

Usefulness of sonication for diagnosing infection in explanted orthopaedic implants

BACKGROUND

Orthopaedic implant infection is a rare but serious complication whose optimal treatment requires an accurate microbiological diagnosis. The objective of this study was to determine whether culturing sonicated explants improved sensitivity compared to culturing standard sonicated soft-tissue samples.

HYPOTHESIS

Cultures of explant sonication fluid are more sensitive than cultures of soft-tissue sonication fluid in patients with implant infection.

METHODS

This single-centre retrospective study included all sonication fluid samples from implants explanted in orthopaedic surgery theatres for any reason. The microbiological results of the implant sonication fluid cultures were compared to those of cultures of sonicated soft-tissue and bone samples taken during the same procedure. The primary evaluation criterion was the difference in microorganisms recovered from explant sonication fluids versus fluid/tissue cultures.

RESULTS

The study included 187 explants removed between September 2009 and June 2015. Of the definite infections, 83% were identified by explant sonication, 86% by fluid/tissue cultures, and 91% by both techniques combined. Explant sonication recovered causative organisms in 10 patients with definite infection but negative fluid/soft tissue cultures. Antibiotic therapy prior to explantation was associated with lower sensitivity of explant sonication (57% vs. 67% for fluid/soft tissue cultures).

CONCLUSION

Explant sonication improved the diagnosis of infection when combined with fluid/soft tissue cultures.

LEVEL OF EVIDENCE

IV, retrospective single-centre study.

Prosthetic Joint Infections: an Update

PURPOSE OF REVIEW

Prosthetic joint infection (PJI) is a rare but serious complication that is frequently misdiagnosed. We aimed to highlight the nuances of PJI diagnosis and antimicrobial therapies and provide clarity in key areas of management.

RECENT FINDINGS

Current research in PJI centers on a potential role for diagnostic biomarkers, molecular techniques, and implant sonication to reduce culture-negativity rates. The optimal duration of antimicrobial therapy remains controversial. A high clinical index of suspicion for PJI combined with data from multiple preoperative and intraoperative tests enables timely diagnosis and treatment. Biomarkers, molecular methods, and implant sonication are currently adjunctive to traditional diagnostic techniques. Shorter courses of antimicrobial therapies as well as the role of chronic suppressive therapy need confirmation by randomized controlled trials. Existing practices for preoperative dental prophylaxis and treatment of asymptomatic bacteriuria warrant revision based on evidence arguing against risk for PJI.

Histopathology in Periprosthetic Joint Infection: When Will the Morphomolecular Diagnosis Be a Reality?

The presence of a polymorphonuclear neutrophil infiltrate in periprosthetic tissues has been shown to correlate closely with the diagnosis of septic implant failure. The histological criterion considered by the Musculoskeletal Infection Society to be diagnostic of periprosthetic joint infection is “greater than five neutrophils per high-power field in five high-power fields observed from histologic analysis of periprosthetic tissue at ×400 magnification.” Surgeons and pathologists should be aware of the qualifications introduced by different authors during the last years in the histological techniques, samples for histological study, cutoffs used for the diagnosis of infection, and types of patients studied. Recently, immunohistochemistry and histochemistry studies have appeared which suggest that the cutoff point of five polymorphonuclear neutrophils in five high-power fields is too high for the diagnosis of many periprosthetic joint infections. Therefore, morphomolecular techniques could help in the future to achieve a more reliable histological diagnosis of periprosthetic joint infection.

3-phase Technicium-99m bone scanning in patients with pain in the hip region after cemented total hip replacement: a multicentre series of 100 cases

INTRODUCTION

The aim of this study was to assess the benefit of a Technetium-99M (HDP) 3-phase bone scan (TPBS) as an additional diagnostic test in the evaluation of pain in the hip region following cemented total hip replacement (THR) surgery.

METHODS

A retrospective study over a 24-month period was performed comprising 100 patients investigated with a TPBS. Investigations were summarised and analysed, and were classified as entirely normal, possibly abnormal, and definitely abnormal.

RESULTS

45% (45) of TPBSs were reported as being entirely normal, 50% (50) as possibly abnormal, and 5% (5) as definitely abnormal. During the 24-month study period 230 revision THR procedures were performed at our institution; 10% (24) were investigated with TPBS and 90% (206) were not. 29% (7/24) of patients investigated with a TPBS that subsequently underwent revision THR surgery had an entirely normal preoperative TPBS. 84% (38) with an abnormal TPBS were managed conservatively. A TPBS had a sensitivity of 29% (95% confidence interval (CI), 13%-51%) and a specificity of 50% (95% CI, 38%-62%) in the detection of infection, or loosening with concurrent infection.

CONCLUSION

A TPBS should only be considered following clinical evaluation, serological investigation, diagnostic imaging and microbiological analysis of fluid obtained from arthrocentesis by a specialist revision arthroplasty surgeon. A TPBS may be useful in the situation where abnormal serology is present, but where repeated joint aspirations samples are inconclusive.

Can next generation sequencing play a role in detecting pathogens in synovial fluid?

Aims

The diagnosis of periprosthetic joint infection can be difficult due to the high rate of culture-negative infections. The aim of this study was to assess the use of next-generation sequencing for detecting organisms in synovial fluid.

Materials and Methods

In this prospective, single-blinded study, 86 anonymized samples of synovial fluid were obtained from patients undergoing aspiration of the hip or knee as part of the investigation of a periprosthetic infection. A panel of synovial fluid tests, including levels of C-reactive protein, human neutrophil elastase, total neutrophil count, alpha-defensin, and culture were performed prior to next-generation sequencing.

Results

Of these 86 samples, 30 were alpha-defensin-positive and culture-positive (Group I), 24 were alpha-defensin-positive and culture-negative (Group II) and 32 were alpha-defensin-negative and culture-negative (Group III). Next-generation sequencing was concordant with 25 results for Group I. In four of these, it detected antibiotic resistant bacteria whereas culture did not. In another four samples with relatively low levels of inflammatory biomarkers, culture was positive but next-generation sequencing was negative. A total of ten samples had a positive next-generation sequencing result and a negative culture. In five of these, alpha-defensin was positive and the levels of inflammatory markers were high. In the other five, alpha-defensin was negative and the levels of inflammatory markers were low. While next-generation sequencing detected several organisms in each sample, in most samples with a higher probability of infection, there was a predominant organism present, while in those presumed not to be infected, many organisms were identified with no predominant organism.

Conclusion

Pathogens causing periprosthetic infection in both culture-positive and culture-negative samples of synovial fluid could be identified by next-generation sequencing. Cite this article: Bone Joint J 2018;100-B:127–33.

Diagnostic accuracy of synovial fluid, blood markers, and microbiological testing in chronic knee prosthetic infections

INTRODUCTION

This retrospective study was undertaken to define cut-off values for synovial fluid (SF) leukocyte count and neutrophil percentage for differentiating aseptic failure and periprosthetic joint infection (PJI) and to evaluate the diagnostic accuracy of blood inflammatory markers, and microbiological testing according to the criteria proposed by the International Consensus Meeting (ICM) of Philadelphia.

METHODS

All patients who underwent revision total knee arthroplasty from January 2010 to July 2015 were included: we identified and classified 31 PJIs and 136 aseptic joints. The diagnostic performance of single test was assessed by receiver operating characteristic curve analyses. The sensitivity and specificity were calculated for each of the cut-off values and the area under the curve (AUC) was calculated.

RESULTS

The median SF leukocyte count as well as the neutrophil percentage and inflammatory markers were significantly higher in patients with PJI than in those with aseptic failure (p < 0.001). A leukocyte count of > 2.8 × 10³/μL had a sensitivity of 83.8% and a specificity of 89.7% whereas a neutrophil percentage of > 72% yielded a marginally higher sensitivity of 84% and a specificity of 91%. Applying the ICM criteria we found a significant correlation between all these diagnostic measures and PJI (p < 0.001) except for a single positive culture. The most accurate criterion of the ICM was the synovial neutrophil differential (AUC = 0.89; 95% CI 0.81-0.97), followed by SF leukocyte count (AUC = 0.86; 95% CI 0.78-0.94), increased inflammatory markers (AUC = 0.85; 95% CI 0.76-0.93), and two positive periprosthetic cultures (AUC = 0.84; 95% CI 0.73-0.94). The presence of sinus tract communicating with the joint and a single positive culture showed unfavourable diagnostic accuracy (AUC = 0.60, 95% CI 0.47-0.72; AUC = 0.49, 95% CI 0.38-0.61, respectively) CONCLUSIONS: The present study highlights the adequate ability of fluid cell count and neutrophil differential to distinguish between PJI and aseptic loosening. The clinical utility of fluid analysis in diagnosing infection can be improved by evaluation of other diagnostic criteria.

LEVEL OF EVIDENCE

Level I Diagnostic Study.

Diagnosis of Periprosthetic Joint Infection: The Potential of Next-Generation Sequencing

BACKGROUND

Next-generation sequencing is a well-established technique for sequencing of DNA and has recently gained attention in many fields of medicine. Our aim was to evaluate the accuracy of next-generation sequencing in identifying the causative organism(s) in patients with periprosthetic joint infection.

METHODS

In this prospective study, samples were collected from 65 revision arthroplasties (39 knees and 26 hips) and 17 primary arthroplasties (9 hips and 8 knees). Synovial fluid, deep tissue, and swabs were obtained at the time of the surgical procedure and were shipped to the laboratory for next-generation sequencing. Deep-tissue specimens were also sent to the institutional laboratory for culture. Sensitivity and specificity were calculated for next-generation sequencing, using the Musculoskeletal Infection Society (MSIS) definition of periprosthetic joint infection as the standard.

RESULTS

In 28 revisions, the cases were considered to be infected; cultures were positive in 17 cases (60.7% [95% confidence interval (CI), 40.6% to 78.5%]), and next-generation sequencing was positive in 25 cases (89.3% [95% CI, 71.8% to 97.7%]), with concordance between next-generation sequencing and culture in 15 cases. Among the 11 cases of culture-negative periprosthetic joint infection, next-generation sequencing was able to identify an organism in 9 cases (81.8% [95% CI, 48.2% to 97.7%]). Next-generation sequencing identified microbes in 9 (25.0% [95% CI, 12.1% to 42.2%]) of 36 aseptic revisions with negative cultures and in 6 (35.3% [95% CI, 14.2% to 61.7%]) of 17 primary total joint arthroplasties. Next-generation sequencing detected several organisms in most positive samples. However, in the majority of patients who were infected, 1 or 2 organisms were dominant.

CONCLUSIONS

Next-generation sequencing may be a useful adjunct in identification of the causative organism(s) in culture-negative periprosthetic joint infection. Our findings suggest that some cases of monomicrobial periprosthetic joint infection may have additional organisms that escape detection when culture is used. Further study is required to determine the clinical implications of isolated organisms in samples from patients who are not thought to be infected.

LEVEL OF EVIDENCE

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

LEVEL OF EVIDENCE

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

Screening for Infection Before Revision Hip Arthroplasty: A Meta-analysis of Likelihood Ratios of Erythrocyte Sedimentation Rate and Serum C-reactive Protein Levels

INTRODUCTION

Diagnosing periprosthetic joint infection (PJI) before revision hip arthroplasty is critical to ensure effective treatment of patients undergoing surgery for reasons other than infection. The main objective of our study is to determine whether the erythrocyte sedimentation rate (ESR) and the serum C-reactive protein (CRP) level are sufficient to use for testing to rule out infection in patients undergoing revision hip surgery.

METHODS

We performed a systematic review of the literature in the MEDLINE, Ovid, and Embase databases. We included studies in which the investigators used the ESR (>30 mm/h) and serum CRP level (>10 mg/L) for the diagnosis of PJI of the hip. We obtained meta-estimates of sensitivity, specificity, positive likelihood ratio (LR+), and negative likelihood ratio (LR-).

RESULTS

From 511 articles, we analyzed 12 studies in which the investigators reported data on 2,736 patients. Sensitivity and specificity for the ESR were 0.860 (95% confidence interval [CI], 0.825 to 0.890) and 0.723 (95% CI, 0.704 to 0.742), respectively, and for the CRP level were 0.869 (95% CI, 0.835 to 0.899) and 0.786 (95% CI, 0.769 to 0.803), respectively. For the ESR, LR+ was 3.42 (95% CI, 2.55 to 4.59) and LR- was 0.22 (95% CI, 0.12 to 0.41). For the CRP level, LR+ was 4.18 (95% CI, 3.42 to 5.11) and LR- was 0.20 (95% CI, 0.12 to 0.32).

DISCUSSION

With a low pretest probability of PJI, a negative test result for either the ESR or CRP level is enough to rule out infection before revision hip arthroplasty.

LEVEL OF EVIDENCE

III.

Are patients being evaluated for periprosthetic joint infection prior to referral to a tertiary care center?

Background

Patients with a painful or failed total joint arthroplasties should be evaluated for periprosthetic joint infection (PJI). The purpose of this study is to determine if patients referred to a tertiary care center had been evaluated for PJI according to the American Academy of Orthopaedic Surgeons (AAOS) clinical practice guidelines.

Methods

One hundred thirteen patients with painful hip (43) or knee (70) arthroplasties were referred to a single provider by orthopaedic surgeons outside our practice between 2012 and 2014. We retrospectively evaluated the workup by referring physicians, including measurement of serum erythrocyte sedimentation rate and C-reactive protein, performance of a joint aspiration if these values were abnormal, and obtainment of synovial fluid white blood cell count, differential, and cultures.

Results

Sixty-two of 113 patients (55%) did not have a workup that followed AAOS guidelines. Serum erythrocyte sedimentation rate and C-reactive protein were ordered for 64 of the 113 patients (57%). Of 25 patients with elevated inflammatory markers warranting aspiration, 15 (60%) had an aspiration attempted, with synovial fluid white blood cell, differential, and cultures obtained in 9 of 12 (75%) aspirations that yielded fluid. Of the 62 patients with an incomplete infection workup, 11 (18%) had a bone scan, 6 (10%) a computed tomography scan, and 3 (5%) a magnetic resonance imaging. Twelve of the 113 patients (11%) were ultimately diagnosed with PJI, with 5 undiagnosed prior to referral.

Conclusions

The AAOS guidelines to evaluate for PJI are frequently not being followed. Improving awareness of these guidelines may avoid unnecessary and costly evaluations and delay in the diagnosis of PJI.

Diagnosis of Streptococcus canis periprosthetic joint infection: the utility of next-generation sequencing

A 62-year-old man who had undergone a primary knee arthroplasty 3 years earlier, presented to the emergency department with an infected prosthesis. He underwent prosthesis resection. All cultures failed to identify the infecting organism. Analysis of the intraoperative samples by next-generation sequencing revealed Streptococcus canis (an organism that resides in the oral cavity of dogs). It was later discovered that the patient had sustained a dog scratch injury several days earlier. The patient reports that his dog had licked the scratch. Treatment was delivered based on the sensitivity of S. canis, and the patient has since undergone reimplantation arthroplasty.

The unsuspected prosthetic joint infection

Aims

Positive cultures are not uncommon in cases of revision total knee and hip arthroplasty (TKA and THA) for presumed aseptic causes. The purpose of this study was to assess the incidence of positive intra-operative cultures in presumed aseptic revision of TKA and THA, and to determine whether the presence of intra-operative positive cultures results in inferior survival in such cases.

Patients and Methods

A retrospective cohort study was assembled with 679 patients undergoing revision knee (340 cases) or hip arthroplasty (339 cases) for presumed aseptic causes. For all patients three or more separate intra-operative cultures were obtained. Patients were diagnosed with a previously unsuspected prosthetic joint infection (PJI) if two or more cultures were positive with the same organism. Records were reviewed for demographic details, pre-operative laboratory results and culture results. The primary outcome measure was infection-free implant survival at two years.

Results

The incidence of unsuspected PJI was 27 out of 340 (7.9%) in TKA and 41 out of 339 (12.1%) in THA. Following revision TKA, the rate of infection-free implant survival in patients with an unsuspected PJI was 88% (95% confidence intervals (CI) 60 to 97) at two years compared with 98% (95% CI 94 to 99) in patients without PJI (p = 0.001). After THA, the rate of survival was similar in those with unsuspected PJI (92% (95% CI 73 to 98) at two years) and those without (94% (95% CI 89 to 97), p = 0.31).

Conclusion

Following revision of TKA and THA for aseptic diagnoses, around 10% of cases were found to have positive cultures. In the knee, such cases had inferior infection-free survival at two years compared with those with negative cultures; there was no difference between the groups following THA. Cite this article: Bone Joint J 2017;99-B:1482–9.

Revision Total Ankle Arthroplasty

With total ankle arthroplasty, documented complications can be categorized chronologically into intraoperative, postoperative, and late complications. Factors such as patient selection, surgeon experience, implant features, and prosthetic device selection can influence functional outcomes as well as incidence of complications. Even with impeccable surgical technique and optimal patient selection, complications that require revision may still arise and the most common complications with revision solutions are discussed in this article.

Fluoroscopy- vs ultrasound-guided aspiration techniques in the management of periprosthetic joint infection: which is the best?

BACKGROUND

Fluid samples obtained from an affected joint still play a central role in the diagnosis of periprosthetic joint infection (PJI). It is the only preoperative test able to discover the causative microbiological agent. In the hip, fluid aspiration can be performed through fluoroscopy, ultrasound, or, less commonly, computed tomography. However, there is still a lack of consensus on which method is preferable in terms of efficacy and costbenefit.

PURPOSES

We, therefore, asked whether (1) the benefits in terms of sensitivity and specificity and (2) the costs were comparable between fluoroscopy- and ultrasound-guided joint aspirations in a suspicious of hip PJI.

METHODS

Between 2013 and 2016, 52 hip aspirations were performed on 49 patients with clinical, radiological, or serological suspicion of PJI, waiting for a revision surgery. The patients were divided in two groups: fluoroscopy- (n = 26) vs ultrasound-guided hip aspiration group (n = 26). These groups were also divided in control and infected patients. The criteria of MusculoSkeletal Infection Society (MSIS) were used, as gold standard, to define PJI.

RESULTS

(1) Ultrasound-guided aspiration revealed valid sensitivity (89% vs 60%) and specificity (94% vs 81%) in comparison with fluoroscopic-guided aspiration. (2) The cost analysis was also in favor of ultrasound-guided aspiration (125.30€) than fluoroscopic-guided aspiration (343.58€).

CONCLUSIONS

We concluded that ultrasound-guided hip aspiration could represent a valid, safe, and less expensive diagnostic alternative to fluoroscopic-guided aspiration in hip PJI.

The Effect of Preoperative Antimicrobial Prophylaxis on Intraoperative Culture Results in Patients with a Suspected or Confirmed Prosthetic Joint Infection: a Systematic Review

Obtaining reliable cultures during revision arthroplasty is important to adequately diagnose and treat a prosthetic joint infection (PJI). The influence of antimicrobial prophylaxis on culture results remains unclear. Since withholding prophylaxis increases the risk for surgical site infections, clarification on this topic is critical. A systematic review was performed with the following research question: in patients who undergo revision surgery of a prosthetic joint, does preoperative antimicrobial prophylaxis affect the culture yield of intraoperative samples in comparison with nonpreoperative antimicrobial prophylaxis? Seven articles were included in the final analysis. In most studies, standard diagnostic culture techniques were used. In patients with a PJI, pooled analysis showed a culture yield of 88% (145/165) in the prophylaxis group versus 95% (344/362) in the nonprophylaxis group (P = 0.004). Subanalysis of patients with chronic PJIs showed positive cultures in 88% (78/89) versus 91% (52/57), respectively (P = 0.59). In patients with a suspected chronic infection, a maximum difference of 4% in culture yield between the prophylaxis and nonprophylaxis groups was observed. With the use of standard culture techniques, antimicrobial prophylaxis seems to affect cultures in a minority of patients. Along with the known risk of surgical site infections due to inadequate timing of antimicrobial prophylaxis, we discourage the postponement of prophylaxis until tissue samples are obtained in revision surgery. Future studies are necessary to conclude whether the small percentage of false-negative cultures after prophylaxis can be further reduced with the use of more-sensitive culture techniques, like sonication.

How Many Cultures Are Necessary to Identify Pathogens in the Management of Total Hip and Knee Arthroplasty Infections?

BACKGROUND

Identification of the infecting organism is critical to the successful management of deep prosthetic joint infections about the hip and the knee. However, the number of culture specimens and which culture specimens are best to identify these organisms is unknown.

METHODS

We evaluated 113 consecutive patients with infected total hip and total knee arthroplasties and correlated the type of culture specimen and number of specimens taken during surgery to the likelihood of a positive culture result. From these data, we subsequently developed a model to maximize culture yield at the time of surgical intervention. After exclusions, 74 patients meeting the Musculoskeletal Infection Society criteria were left for final analysis.

RESULTS

From this cohort, 63 of 74 patients had a positive culture result (85%). The odds of a fluid culture result being positive was 35 of 47 (0.75), whereas the likelihood of tissue cultures yielding a positive result was 164 of 245 (0.67; P = .313). The sample designated "best culture" specimen was the only culture with a positive result in 1 of 48 cases in which a best culture was identified. The optimal number of cultures needed to yield a positive test result was 4 (specificity = 0.61 and sensitivity = 0.63). Increasing the number of samples increases sensitivity but reduces specificity.

CONCLUSION

A minimum of 4 tissue cultures from representative areas is necessary to maximize the chance of identifying the infecting organism during management of the infected total hip and total knee arthroplasties. The designation of the best culture specimen for additional testing is arbitrary and may not be clinically efficacious.

Withholding Preoperative Antibiotic Prophylaxis in Knee Prosthesis Revision: A Retrospective Analysis on Culture Results and Risk of Infection

BACKGROUND

A significant amount of patients undergoing revision surgery of a prosthetic joint turn out to have an infection. Withholding preoperative antibiotic prophylaxis in these patients to optimize culture yield during revision surgery remains a matter of debate. The aim of our study was to determine (1) the rate of positive intraoperative cultures with or without preoperative antibiotic prophylaxis and (2) the incidence of a prosthetic joint infection (PJI) during the follow-up in the 2 groups.

METHODS

Medical files of patients in whom preoperative antibiotic prophylaxis was withheld until culture samples were taken (2007-2010, n = 284) and in whom antibiotic prophylaxis was given during the induction of anesthesia (2010-2013, n = 141) were retrospectively reviewed.

RESULTS

The percentage of ≥1 positive cultures was the same in the group without (26%) and with preoperative prophylaxis (27%; P value, .7). PJI was diagnosed during revision surgery according to the Musculoskeletal Infection Society criteria in 6.7% patients not receiving preoperative prophylaxis and in 7.0% receiving it (P value, .79). We found no important differences in the type of microorganisms that were isolated in both groups. During a 3-month follow-up, an early PJI developed in patients undergoing total revision surgery in 6.4% of the nonpreoperative prophylaxis group vs 1.6% in the preoperative prophylaxis group (P value, .1).

CONCLUSION

Preoperative antibiotic prophylaxis does not reduce culture yield in patients undergoing knee revision surgery. Our data show a trend toward a higher PJI rate in the postoperative period of total revision surgery when preoperative prophylaxis is withheld.

Inadequacy of Joint Aspiration for Detection of Persistent Periprosthetic Infection During Two-Stage Septic Revision Knee Surgery

Despite the lack of validation, synovial aspiration remains a common practice during 2-stage septic revision total knee arthroplasty (TKA). The goal of this study was to investigate the diagnostic validity of synovial polymethylmethacrylate (PMMA) spacer aspiration of temporary knee arthrodesis to detect persistent periprosthetic joint infection before TKA reimplantation. This retrospective cohort study included 73 consecutive patients who underwent 2-stage septic revision TKA according to a standard protocol. After explantation surgery, including temporary arthrodesis with an intramedullary stabilized PMMA spacer, all patients had synovial aspiration 2 weeks before reimplantation to exclude persistent periprosthetic joint infection. Patients had a 2-week antibiotic holiday before aspiration. Sensitivity and specificity of the synovial PMMA spacer joint aspiration for the detection of periprosthetic joint infection were determined and referenced against intraoperative microbiologic and histologic samples obtained at second-stage surgery. Sensitivity of the synovial PMMA spacer aspiration was 21%. Because of poor diagnostic validity, synovial PMMA spacer aspiration cannot be recommended for routine exclusion of persistent periprosthetic joint infection before TKA reimplantation. Therefore, exclusion of persistent periprosthetic joint infection should be supplemented by other diagnostic methods, and it is not necessary to delay TKA reimplantation for PMMA spacer aspiration. [Orthopedics. 2017; 40(4):231-234.].

Sonication of Arthroplasty Implants Improves Accuracy of Periprosthetic Joint Infection Cultures

BACKGROUND

There is evidence that sonication of explanted prosthetic hip and knee arthroplasty components with culture of the sonication fluid may enhance diagnostic sensitivity. Previous studies on the use of implant sonicate cultures have evaluated diagnostic thresholds but did not elaborate on the clinical importance of positive implant sonicate cultures in the setting of presumed aseptic revisions and did not utilize consensus statements on periprosthetic joint infection (PJI) diagnosis when defining their gold standard for infection.

QUESTIONS/PURPOSES

(1) How do implant sonicate cultures compare with preoperative synovial fluid cultures and intraoperative tissue cultures in the diagnosis of PJI in both THA and TKA when compared against Musculoskeletal Infection Society (MSIS) criteria for PJI? (2) Utilizing implant sonicate cultures, what is the relative prevalence of bacterial species identified in PJIs? (3) What is the incidence of positive implant sonicate cultures in the setting of presumed aseptic revision hip and knee arthroplasty procedures, and what treatments did they receive?

METHODS

Between 2012 and 2016 we performed implant sonicate fluid cultures on surgically removed implants from 565 revision THAs and TKAs. Exclusion criteria including insufficient data to determine Musculoskeletal Infection Society (MSIS) classification, fungal-only cultures, and absence of reported colony-forming units decreased the number of procedures to 503. Procedures represented each instance of revision surgery (sometimes multiple in the same patient). Of those, a definitive diagnosis of infection was made using the MSIS criteria in 178 of 503 (35%), whereas the others (325 of 503 [65%]) were diagnosed as without infection. A total of 53 of 325 (16%) were considered without infection based on MSIS criteria but had a positive implant sonicate culture. Twenty-five of 53 (47%) of these patients were followed for at least 2 years. The diagnosis of PJI was determined using the MSIS criteria.

RESULTS

Sensitivity of implant sonicate culture was greater than synovial fluid culture and tissue culture (97% [89%-99%] versus 57% [44%-69%], p < 0.001; 97% [89%-99%] versus 70% [58%-80%], p < 0.001, respectively). The specificity of implant sonicate culture was not different from synovial fluid culture or tissue culture with the numbers available (90% [72%-97%] versus 100% [86%-100%], p = 0.833; 90% [72%-97%] versus 97% [81%-100%], p = 0.317, respectively). Coagulase-negative Staphylococcus was the most prevalent organism for both procedure types. In PJIs, the five most frequent bacteria identified by synovial fluid, tissue, and/or implant sonicate cultures were coagulase-negative Staphylococcus (26% [89 of 267]), methicillin-susceptible Staphylococcus aureus (19% [65 of 267]), methicillin-resistant S. aureus (12% [43 of 267]), α-hemolytic Streptococci (5% [19 of 267]), and Enterococcus faecalis (5% [19 of 267]). Fifty-three of 325 (16%) presumed aseptic revisions had a positive sonication culture. Thirty-four percent (18 of 53) of culture-positive aseptic revision patients received antibiotic treatment for infection and 8% (4 of 53) underwent a secondary revision.

CONCLUSIONS

The routine use of implant sonicate cultures in arthroplasty revisions improves the diagnostic sensitivity for detecting the presence of bacteria in both clinical and occult infections. Future studies will need to refine colony-forming unit thresholds for determining clinical infection and indications for treatment.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Diagnosis of Periprosthetic Joint Infection-An Algorithm-Based Approach

BACKGROUND

Periprosthetic joint infection (PJI) remains one of the most challenging and devastating modes of failure after total hip and knee arthroplasties. Despite the profound urgency and impact of PJI on an individual and societal basis, historically, there have not been standardized definitions of and diagnostic algorithms for infection after total joint arthroplasty.

METHODS

In a recent symposium, the American Academy of Hip and Knee Surgeons put forth a standardized approach to the prevention, diagnosis, and management of the patient with a suspected PJI.

RESULTS

This review article summarizes these findings, and reviews the algorithmic approach to the diagnosis of PJI.

CONCLUSION

The diagnosis of PJI is easily made in our experience in 90% of patients by getting an erythrocyte sedimentation rate and C-reactive protein followed by selective aspiration of the joint if these values are elevated or if the clinical suspicion is high. Synovial fluid obtained should be sent for a synovial fluid white blood cell count, differential, and cultures.

False-positive Cultures After Native Knee Aspiration: True or False

BACKGROUND

Synovial fluid aspiration is a routine practice used by most orthopaedic surgeons to aid in the diagnosis of joint infection. In patients for whom there is a low pretest probability of infection, a positive culture-particularly if it is a broth-only culture-may be considered a contaminant, especially if the bacterial species are skin pathogens. To our knowledge no study has evaluated the incidence of contamination of aspirations from the native knee.

QUESTIONS/PURPOSES

What is the frequency of false-positive cultures among knee aspirations of the native knee?

METHODS

Two hundred patients, with a total of 200 knees, with the diagnosis of degenerative osteoarthritis undergoing a total knee arthroplasty (TKA) were identified for this study. None of these patients had symptoms, signs, or laboratory studies to suggest the presence of joint infection; a positive culture in this population therefore would be considered contaminated. Thirty-two (16%) patients were excluded secondary to a dry aspiration. One patient was enrolled in the study but did not have the knee aspirated and another patient's specimen was accidentally discarded. Each knee was aspirated under sterile conditions before performing the TKA. The fluid was sent for cell count and culture. If insufficient fluid was obtained for both cell count and culture, culture was performed rather than cell count.

RESULTS

There were no false-positive cultures (zero of 166 [0%]) in aspirations of native knees.

CONCLUSIONS

Our study would indicate that when done properly under sterile technique, cultures taken from knee arthrocentesis in patients without prosthetic joints should not be affected by perceived contaminant species. A positive specimen finding on culture should raise a strong suspicion of bacterial septic arthritis. Future studies should include more specimens as well as knees with prior TKA to help further identify the rate of false-positive cultures in knee arthrocentesis in both populations.

LEVEL OF EVIDENCE

Level I, diagnostic study.

Low sensitivity of implant sonication when screening for infection in revision surgery

Background and purpose - Prosthetic-joint infection (PJI) is the most serious complication of arthroplasty, and accurate identification of a potentially responsible microorganism is essential for successful antibiotic treatment. We therefore determined the diagnostic accuracy of sonication and compared it with tissue culture as a screening tool in detecting prosthetic joint infection in revision arthroplasty. Patients and methods - 252 consecutive revision arthroplasty cases were enrolled. These cases were determined as being suspected or unsuspected of having infection according to standard criteria. Perioperatively, 6 periprosthetic interface tissue biopsies were obtained from each patient and the implants removed were sonicated. The sensitivity and specificity of periprosthetic tissue culture and sonication fluid cultures were determined. Results - Preoperatively, 75 revision cases were classified as having PJI (33 early and 42 late) and 177 were unsuspected of having infection. Compared with tissue culture, the sensitivity of the sonication fluid analysis was low: 0.47 (95% CI: 0.35-0.59) for sonication as compared to 0.68 (95% CI: 0.56-0.78) for tissue culture. The specificity of the sonication fluid analysis was higher than that for tissue culture: 0.99 (95% CI: 0.96-1.0) as compared to 0.80 (95% CI: 0.74-0.86). Interpretation - Sonication is a highly specific test for diagnosis of PJI. However, due to the low sensitivity, a negative sonication result does not rule out the presence of PJI. Thus, sonication is not of value for screening of microorganisms during revision surgery.

How To Diagnose and Treat Infection in Total Ankle Arthroplasty

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

Functional outcomes of infected hip arthroplasty: a comparison of different surgical treatment options

BACKGROUND

Periprosthetic joint infection (PJI) following total hip arthroplasty (THA) can be treated with irrigation and debridement with head and polyethylene exchange (IDHPE) or 2-stage revision (2SR). Few studies have compared patient-reported outcome measures (PROMs) in patients managed with these treatments.

METHODS

A retrospective review identified 137 patients who had an infected primary THA between 1986-2013. Control cohorts were matched according to age and Charlton Comorbidity Index (CCI). Harris Hip Scores (HHS), Short Form 12 (SF12), and Western Ontario and McMaster Universities Arthritis Index (WOMAC) scores were compared between the control and infected cohorts.

RESULTS

68 patients underwent a 2SR and 69 patients underwent an IDHPE. IDHPE had a 59% success rate in eradicating infection. PROMs for the 2SR cohort were significantly worse than the noninfected controls (SF12-PCS [34.0 vs. 38.3, p = 0.03]; HHS [76.6 vs. 91.7, p<0.001]; and WOMAC [67.3 vs. 79.3, p = 0.005]). There were no significant differences between the noninfected cohort and the successful IDHPE. Significant differences were found between failed IDHPE and noninfected controls (SF12-PCS [42.5 vs. 34.0, p = 0.011]; HHS [92.3 vs. 79.6, p = 0.004]). There was only difference in SF12-MCS scores (50.3 vs. 57.3, p = 0.012) between the 2SR and failed IDHPE cohorts.

CONCLUSIONS

Patients treated with a successful IDHPE had similar outcomes to noninfected patients. Patients that failed IDHPE and went onto 2SR had similar outcomes to those that had a 2SR alone. IDHPE demonstrated a 59% success rate with PROMs equivalent to a noninfected cohort and should be considered in the treatment algorithm of infected THA.

Synovial Fluid Cell Count for Diagnosis of Chronic Periprosthetic Hip Infection

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

LEVEL OF EVIDENCE

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

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

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

Outcome of Total Hip and Total Knee Revision Arthroplasty With Minor Infection Criteria: A Retrospective Matched-Pair Analysis

BACKGROUND

Although diagnostic modalities for the detection of periprosthetic joint infection have improved, some infectious revision cases may still be diagnosed as aseptic complications. We raised the question whether patients with positive Musculoskeletal Infection Society minor infection criteria differ in their outcome parameters (revision-free survival, revision rate) when compared to patients with "true" aseptic complications. Additionally, we asked whether the indication for revision surgery (eg, loosening) might have an influence on possible outcome discrepancies.

METHODS

A retrospective matched-pair analysis was performed with 98 patients who had undergone revision surgery after total joint arthroplasty. Forty-nine patients showed less than 3 positive minor criteria (PMC), whereas 49 patients without any PMC were compared regarding re-revision rate and revision-free survival. Reasons for revisions were categorized according to loosening, liner wear, implant failure, and soft-tissue complication.

RESULTS

In the group of patients with PMC, 30.6% (n = 15) had to undergo re-revision compared to 6.12% (n = 3) in the true aseptic complication control group. The long-term implant survival in the PMC group was 69.4% (95% confidence interval [CI], 47-69 months) and in the aseptic control group was 93.9% (95% CI, 82-94 months; P = .001). In patients with PMC and loosening of the implant, the long-term survival was 55.2% (95% CI survival time, 28.9-53.2 months) whereas in patients without PMC and loosening, the overall survival was 96.2% (95% CI survival time, 83.5-96 months; P = .001).

CONCLUSION

Our findings suggest that in the presence of prosthetic loosening, even a single positive minor criterion may have a negative impact on the outcome after total hip arthroplasty and total knee arthroplasty revision surgeries.

Prosthetic joint infection development of an evidence-based diagnostic algorithm

BACKGROUND

Increasing rates of prosthetic joint infection (PJI) have presented challenges for general practitioners, orthopedic surgeons and the health care system in the recent years. The diagnosis of PJI is complex; multiple diagnostic tools are used in the attempt to correctly diagnose PJI. Evidence-based algorithms can help to identify PJI using standardized diagnostic steps.

METHODS

We reviewed relevant publications between 1990 and 2015 using a systematic literature search in MEDLINE and PUBMED. The selected search results were then classified into levels of evidence. The keywords were prosthetic joint infection, biofilm, diagnosis, sonication, antibiotic treatment, implant-associated infection, Staph. aureus, rifampicin, implant retention, pcr, maldi-tof, serology, synovial fluid, c-reactive protein level, total hip arthroplasty (THA), total knee arthroplasty (TKA) and combinations of these terms.

RESULTS

From an initial 768 publications, 156 publications were stringently reviewed. Publications with class I-III recommendations (EAST) were considered. We developed an algorithm for the diagnostic approach to display the complex diagnosis of PJI in a clear and logically structured process according to ISO 5807.

CONCLUSIONS

The evidence-based standardized algorithm combines modern clinical requirements and evidence-based treatment principles. The algorithm provides a detailed transparent standard operating procedure (SOP) for diagnosing PJI. Thus, consistently high, examiner-independent process quality is assured to meet the demands of modern quality management in PJI diagnosis.

Diagnostic accuracy of arthroscopic biopsy in periprosthetic infections of the hip

Background

Diagnosis of a low-grade periprosthetic joint infection (PJI) prior to revision surgery can be challenging, despite paramount importance for further treatment. Arthroscopic biopsy of synovial and periprosthetic tissue with subsequent microbiological and histological examination can be beneficial but its specific diagnostic value has not been clearly defined.

Methods

20 consecutive patients who underwent percutaneous synovial fluid aspiration as well as arthroscopic biopsy due to suspected PJI of the hip and subsequent one- or two-stage revision surgery at our institution between January 2012 and May 2015 were enrolled. Indication was based on the criteria (1) history of PJI and increased levels of erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP), (2) suspicious cell count and differential but negative bacterial culture in synovial aspirate, (3) early loosening (<less than 2 years), or (4) persisting pain without loosening but history of a PJI. At least two criteria had to be fulfilled in order to perform an arthroscopic biopsy.

Results

Best overall diagnostic value was identified for arthroscopic biopsy and a combination of bacteriological and histological analysis with a sensitivity of 87.5%, specificity of 100% and accuracy of 95%. Bacteriological assessment of synovial aspirate revealed a sensitivity of 50.0%, specificity of 91.7%, and accuracy of 75%. ESR and CRP yielded a sensitivity of 75.0% for either hematologic test and specificities of 87.5 and 66.7%, respectively.

Conclusions

In conclusion, our data indicate that arthroscopic biopsy is superior to ESR and CRP as well as joint aspiration and their combinations. Concurrent microbiological and histological examination of the biopsy specimens allows for identification of the causative pathogen and its susceptibility pattern in order to preoperatively plan the surgical strategy as well as the antibiotic regimen. Moreover, intraarticular mechanical failure can be detected during hip arthroscopy emphasizing its diagnostic value. Level II diagnostic study.

How Do Preoperative Antibiotics Affect Culture Yield in Diabetic Foot Infections?

The impact of preoperative antibiotics on culture of diabetic foot infection samples has not been studied. We found that increasing exposure to preoperative antibiotics was associated with less frequent growth of streptococci and anaerobes and more culture-negative results. In contrast, the yield of Staphylococcus aureus and Gram-negative bacilli was unaffected.

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

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

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

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

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

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