Elie Ghanem

Periprosthetic Joint Infection: The Incidence, Timing, and Predisposing Factors

AbstractPeriprosthetic joint infection is one of the most challenging complications of joint arthroplasty. We identified current risk factors of periprosthetic joint infection after modern joint arthroplasty, and determined the incidence and timing of periprosthetic joint infection. We reviewed prospectively collected data from our database on 9245 patients undergoing primary hip or knee arthroplasty between January 2001 and April 2006. Periprosthetic joint infections developed in 63 patients (0.7%). Sixty-five percent of periprosthetic joint infections developed within the first year of the index arthroplasty. The infecting organism was isolated in 57 of 63 cases (91%). The most common organisms identified were Staphylococcus aureus and Staphylococcus epidermidis. We identified the following independent predictors for periprosthetic joint infection: higher American Society of Anesthesiologists score, morbid obesity, bilateral arthroplasty, knee arthroplasty, allogenic transfusion, postoperative atrial fibrillation, myocardial infarction, urinary tract infection, and longer hospitalization. This study confirmed some previously implicated factors and identified new variables that predispose patients to periprosthetic joint infection. Level of Evidence: Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Cell Count and Differential of Aspirated Fluid in the Diagnosis of Infection at the Site of Total Knee Arthroplasty

BACKGROUND Although there is no absolute diagnostic test for periprosthetic infection, the synovial fluid leukocyte count and neutrophil percentage have been reported to have high sensitivity and specificity. However, the cutoff values for these tests are not agreed upon. We sought to identify definite cutoff values for both the fluid leukocyte count and the neutrophil percentage that may help to diagnose infection at the site of a prosthetic joint. METHODS We analyzed synovial fluid that had been aspirated preoperatively from 429 knees that had undergone revision arthroplasty at three different academic institutions; 161 knees were found to be infected, and 268 knees were not. Using receiver operating characteristic curves, we determined cutoff values for the fluid leukocyte count and neutrophil differential with an optimal balance of sensitivity and specificity for the diagnosis of periprosthetic infection. The sensitivity, specificity, and predictive values were calculated for those cutoff values. The erythrocyte sedimentation rate and C-reactive protein level cutoff values of 30 mm/hr and 10 mg/L, respectively, were combined with the cutoff values for the fluid leukocyte count and neutrophil percentage. RESULTS The cutoff values for optimal accuracy in the diagnosis of infection were >1100 cells/10(-3)cm(3) for the fluid leukocyte count and >64% for the neutrophil differential. When both tests yielded results below their cutoff values, the negative predictive value of the combination increased to 98.2% (95% confidence interval, 95.5% to 99.5%), whereas when both tests yielded results greater than their cutoff values, infection was confirmed in 98.6% (95% confidence interval, 94.9% to 99.8%) of the cases in our cohort. Similarly, when both the neutrophil percentage and the C-reactive protein level were less than the cutoff values of 64% and 10 mg/L, respectively, the presence of periprosthetic infection was very unlikely. CONCLUSIONS The synovial fluid leukocyte count and differential are useful adjuncts to the erythrocyte sedimentation rate and the C-reactive protein level in the preoperative workup of infection at the site of a total knee arthroplasty. The present study identified cutoff values for the leukocyte count (>1100 cells/10(-3)cm(3)) and neutrophil percentage (>64%) that can be used to diagnose infection. Combining the peripheral blood tests with the synovial fluid cell count and differential can improve their diagnostic value.

Periprosthetic infection: what are the diagnostic challenges?

Periprosthetic infection remains one of the most challenging complications of total joint arthroplasty. Despite the substantial reduction in the prevalence of this complication over the last two decades, periprosthetic infection is the second most common complication of joint arthroplasty, after loosening1,2. Infection has been reported to occur in association with 1% to 4% of primary total knee arthroplasties3,4 and about 1% of primary total hip arthroplasties5,6. The prevalence of periprosthetic infection after revision arthroplasty is much higher, reported to be 3.2% for hips and 5.6% for knees7. It is believed that the prevalence of periprosthetic infection is on the rise once again8. The treatment of periprosthetic infection differs vastly from the treatment of aseptic loosening. Hence, it is paramount to distinguish between septic and aseptic joint failures preoperatively. The diagnosis of infection after total joint arthroplasty continues to pose a challenge, particularly when it presents as a subacute or low-grade infection. Currently, there is no universally accepted diagnostic test or modality that is absolutely accurate or reliable for the determination of infection. The diagnosis of periprosthetic infection relies on clinical suspicion and a combined armamentarium of serological and imaging modalities9, with isolation of organisms from the intraoperative culture samples constituting the “gold standard” for ultimate diagnosis10,11. Serological tests, including the erythrocyte sedimentation rate and the C-reactive protein level, are frequently used to screen for septic and aseptic failure of total joint arthroplasty and have a relatively high sensitivity and specificity when combined12. However, their specificity and sensitivity vary depending on the cutoff values chosen10. The role of analysis of synovial fluid for determination of the leukocyte count and neutrophil percentage, although frequently employed, remains unclear. …

Diagnosis of Periprosthetic Joint Infection: The Utility of a Simple Yet Unappreciated Enzyme

BACKGROUND The white blood-cell count and neutrophil differential of the synovial fluid have been reported to have high sensitivity and specificity in the diagnosis of periprosthetic infection following total knee arthroplasty. We hypothesized that neutrophils recruited into an infected joint secrete enzymes that may be used as markers for infection. In this prospective study, we determined the sensitivity and specificity of one of these enzymes, leukocyte esterase, in diagnosing periprosthetic joint infection. METHODS Between May 2007 and April 2010, synovial fluid was obtained preoperatively from the knees of patients with a possible joint infection and intraoperatively from the knees of patients undergoing revision knee arthroplasty. The aspirate was tested for the presence of leukocyte esterase with use of a simple colorimetric strip test. The color change (graded as negative, trace, +, or ++), which corresponded to the level of the enzyme, was noted after one or two minutes. RESULTS On the basis of clinical, serological, and operative criteria, thirty of the 108 knees undergoing revision arthroplasty were infected and seventy-eight were uninfected. When only a ++ reading was considered positive, the leukocyte esterase test was 80.6% sensitive (95% confidence interval [CI], 61.9% to 91.9%) and 100% specific (95% CI, 94.5% to 100.0%), with a positive predictive value of 100% (95% CI, 83.4% to 100.0%) and a negative predictive value of 93.3% (95% CI, 85.4% to 97.2%). The leukocyte esterase level correlated strongly with the percentage of polymorphonuclear leukocytes (r = 0.7769) and total white blood-cell count (r = 0.5024) in the aspirate as well as with the erythrocyte sedimentation rate (r = 0.6188) and C-reactive protein level (r = 0.4719) in the serum. CONCLUSIONS The simple colorimetric strip test that detects the presence of leukocyte esterase in synovial fluid appears to be an extremely valuable addition to the physicians armamentarium for the diagnosis of periprosthetic joint infection. The leukocyte esterase reagent strip has the advantages of providing real-time results, being simple and inexpensive, and having the ability to both rule out and confirm periprosthetic joint infection. However, additional multicenter studies are required to substantiate the results of our preliminary investigation before the reagent strip can be used confidently in the clinic or intraoperative setting.

Diagnosis of Infected Total Knee: Findings of a Multicenter Database

AbstractAlthough total knee arthroplasty (TKA) is an effective and successful procedure, the outcome is occasionally compromised by complications including periprosthetic joint infection (PJI). Accurate and early diagnosis is the first step in effectively managing patients with PJI. At the present time, diagnosis remains dependent on clinical judgment and reliance on standard clinical tests including serologic tests, analysis of aspirated joint fluid, and interpretation of intraoperative tissue and fluid test results. Although reports regarding sensitivity and specificity of all diagnostic tests in the literature are abundant, the interpretation of the available data has been hampered by the low sample size of these studies. In view of the scope of this important problem and the limitations of previous reports, a large database was assembled of all revision TKA performed at three academic referral centers in order to determine the current status of diagnosis of the infected TKA utilizing commonly available tests. Intraoperative cultures should not be used as a gold standard for PJI owing to high percentages of false-negative and false-positive cases. When combined with clinical judgment, total white cell count and percentage of neutrophils in the synovial fluid more accurately reflects PJI and when combined with hematologic exams safely excludes or confirms infection. Level of Evidence: Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Irrigation and debridement in the management of prosthetic joint infection: traditional indications revisited.

Irrigation and debridement (I and D) is a procedure commonly used for the treatment of acute periprosthetic infection. This study retrospectively reviewed clinical records of patients with periprosthetic infection of the hip or knee who underwent I and D with retention of their prostheses between 1997 and 2005 at a single institution. One hundred four patients (44 males and 60 females) were identified. Mean age at time of initial debridement was 65 years. Average follow-up was 5.7 years. Treatment failure was defined as the need for resection arthroplasty or recurrent microbiologically proven infection. According to these criteria, I and D was successful in 46 patients (44%). Patients with staphylococcal infection, elevated American Society of Anesthesiologists score, and purulence around the prosthesis were more likely to fail. The high failure rate of this procedure implies that it should be preferably limited to select healthy patients with low virulence organisms and equivocal intraoperative findings.

FDG-PET imaging can diagnose periprosthetic infection of the hip.

AbstractA battery of diagnostic tests is often required to differentiate aseptic loosening from periprosthetic infection since the gold standard remains elusive. We designed a prospective study to determine the accuracy of fluorodeoxyglucose positron emission tomography (FDG-PET) imaging in diagnosing periprosthetic infection in a large multicenter setting. One hundred and thirteen patients with 127 painful hip prostheses were evaluated by FDG-PET. Images were considered positive for infection if PET demonstrated increased FDG activity at the bone-prosthesis interface of the femoral component. A combination of preoperative tests, intraoperative findings, histopathology, and clinical followup constituted the gold standard for diagnosing infection. Among the 35 positive PET scans, 28 hips were confirmed infected according to our criteria for diagnosing periprosthetic infection. Of the 92 hip prostheses with negative FDG-PET findings, 87 were considered aseptic. The sensitivity, specificity, positive and negative predictive values for FDG-PET were 0.85 (28 of 33), 0.93 (87 of 94), 0.80 (28 of 35), and 0.95 (87 of 92), respectively. The overall accuracy of this novel noninvasive imaging modality reached 0.91 (115 of 127). Based on our results, FDG-PET appears a promising and accurate diagnostic tool for distinguishing septic from aseptic painful hip prostheses. Level of Evidence: Level II, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

The use of receiver operating characteristics analysis in determining erythrocyte sedimentation rate and C-reactive protein levels in diagnosing periprosthetic infection prior to revision total hip arthroplasty

BACKGROUND Periprosthetic infection (PPI) is a difficult complication in total joint arthroplasty, and while erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are acute phase reactants thought to be of high predictive value for diagnosing infection, no clear cut-off values have been defined. The current study aimed to determine the cut-off values for ESR and CRP that improve clinical differentiation between aseptic failure and PPI in total hip arthroplasty (THA). METHODS Four hundred and seventy-nine patients who underwent revision THA for either aseptic mechanical failure or PPI during the period of 2000 to 2005 were included in the study. Specific exclusion criteria were applied to eliminate inflammatory or other confounding conditions. All patients underwent preoperative testing of ESR and CRP. Receiver operating characteristic (ROC) curves were constructed to determine maximum sensitivity and specificity. RESULTS Patients with PPI had significantly higher ESR and CRP values compared to patients undergoing revision for aseptic etiologies. An ESR threshold of 30 mm/h gave a sensitivity of 94.3% and a CRP threshold of 10 mg/l gave a sensitivity of 91.1%. Combining both ESR and CRP cut-offs for a positive diagnosis increased the sensitivity to 97.6%. However, when calculated by ROC analysis, the predictive cut-offs equated to 31 mm/h for ESR and 20.5 mg/l for CRP. CONCLUSIONS The gold standard for diagnosing PPI remains bacterial culture, but sensitivity is negatively affected by prior antibiotic exposure, strongly adherent bacteria, slow growing persisters, and biofilms. ESR and CRP are reflective of systemic changes in infection and pose an attractive, less invasive alternative with reasonable sensitivity and specificity. The current study is the first to identify ideal cut-off values for ESR and CRP in THA patients, providing an optimum balance between sensitivity and specificity based on ROC curves.

Staged Revision for Knee Arthroplasty Infection: What Is the Role of Serologic Tests Before Reimplantation?

Erythrocyte sedimentation rate and C-reactive protein are common preoperative diagnostic markers for prosthetic joint infection but their prognostic role before reimplantation has yet to be defined. We therefore determined the prognostic value of erythrocyte sedimentation rate and C-reactive protein performed before second-stage reimplantation for the treatment of infected total knee arthroplasty (TKA). We studied 109 patients who had undergone two-stage revision TKA for sepsis from 1999 to 2006. Receiver operating characteristic curves were constructed to determine the discriminatory value of erythrocyte sedimentation rate and C-reactive protein before reimplantation in predicting persistent infection. Twenty-three of the 109 patients (21%) required revision surgery for recurrence of prosthetic joint infection. The receiver operating characteristic areas under the curve suggested erythrocyte sedimentation rate and C-reactive protein poorly predicted persistent infection after TKA reimplantation. Cutoff values could not be obtained because of the high variance. We reached similar conclusions regarding the change in erythrocyte sedimentation rate and C-reactive protein levels from time of resection. More accurate diagnostic tools are needed to support clinical judgment in monitoring infection progress and thus deciding whether to proceed with TKA reimplantation.Level of Evidence: Level II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

A simple, cost-effective screening protocol to rule out periprosthetic infection.

The differential diagnosis of pain after total knee arthroplasty includes infection. Effective screening tools should have high sensitivity and are cost-effective. We evaluated 296 patients who underwent total knee revision at our institution. One hundred sixteen patients (39%) were classified as infected and 180 patients (61%) were considered noninfected. The mean erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) of the infected patients were 85 mm/h and 110 mg/L, respectively. The mean ESR and CRP of the noninfected patients were 22 mm/h and 7 mg/L, respectively. Five patients (4%) in the infected group had both normal ESR and CRP. Infection was suspected in all 5 patients, and an organism was cultured in 4 of the 5 cases. Erythrocyte sedimentation rate and CRP, when used in combination, serve as a useful screening tool in patients with a painful total knee arthroplasty.