Ultrasound for diagnosis of infection in revision total hip arthroplasty

The Value of Preoperative Ultrasound-Determined Fluid Film and Joint Aspiration in Revision Hip Arthroplasty

BACKGROUND

Data regarding the diagnostic value of ultrasound (US)-determined fluid film and joint aspiration prior to revision total hip arthroplasty for suspected periprosthetic joint infections (PJIs) are limited. This study aimed to analyze the value of US-determined fluid film, characterized the preoperative and intraoperative microbiological spectrum and resistance patterns, and compared the concordance between preoperative synovial fluid and intraoperative culture results.

METHODS

We analyzed 366 US examinations from 324 patients prior to revision total hip arthroplasty. Selected cases were grouped into clearly infected, noninfected, and inconclusive cohorts, according to the International Consensus Meeting 2018 Criteria. For US-determined fluid film <1 mm, no aspiration was performed based on our institutional protocol. Patients were grouped into no aspiration (144 of 366; [39.3%]), dry tap (21 of 366; [5.7%]), and a successful tap (201 of 366; [54.9%]). The microbiological spectrum and antibiograms were compared between preoperative and intraoperative results.

RESULTS

The absence of US-determined fluid film showed no correlation with the presence of a hip PJI. Overall, 31.9% cases of the no-aspiration group had a PJI. In total, 13.5% discrepancies were found between successful taps and intraoperative cultures. The most prevalent microorganisms in preoperative synovial fluid were Staphylococcus epidermidis and Staphylococcus aureus (20.8%), while intraoperatively S. epidermidis (26.3%) and Cutibacterium acnes (14.5%) were leading. Additional microorganisms were identified in 32.5% of intraoperative cultures. There were no differences between resistance patterns of preoperative and intraoperative concordant microorganisms.

CONCLUSIONS

Absence of US-determined fluid film cannot rule out the presence of a hip PJI. Combined microbiological results from hip US aspirations and subsequent surgical procedures are crucial to design an effective treatment for suspected hip PJI.

Is ultrasound-guided hip aspiration more successful than fluoroscopic-guided aspiration in diagnosing prosthetic joint infection?

Introduction: aspiration of total hip arthroplasty (THA) is commonly performed to assist in the diagnosis of prosthetic joint infection (PJI). This study aimed to determine whether fluoroscopic- or ultrasound- guided hip aspiration differs in the ability to acquire synovial fluid and in the accuracy of diagnosing infection. Methods: all THA aspirations performed between 2014 and 2021 at our institution were retrospectively identified. Aspirations were classified as successful or dry. If successful, the volume of fluid obtained was recorded. The sensitivity and specificity of hip aspiration in identifying PJI were calculated with four methods: (1) culture results excluding saline lavage, (2) culture results including saline lavage, (3) 2018 Musculoskeletal Infection Society (MSIS) International Consensus Meeting (ICM) criteria, and (4) 2021 European Bone and Joint Infection Society (EBJIS) criteria. Analyses were performed using Student's t test or Wilcoxon rank sum for continuous variables and chi-squared or Fisher's exact test for categorical variables. Results: 290 aspirations were included (155 fluoroscopic-guided and 135 ultrasound-guided). Success of aspiration (> 0.5  mL) was more common in the ultrasound cohort (69 %) than fluoroscopy (53 %) (p < 0.0055 ). When successful, more volume was obtained in the ultrasound cohort (mean 13.1 mL vs. 10.0 mL; p = 0.0002 ). Ultrasound-guided aspiration was more sensitive than fluoroscopy in diagnosing PJI using culture results excluding saline lavage (85 % vs. 73 %; p = 0.03 ), culture results including saline lavage (85 % vs. 69 %; p = 0.001 ), 2018 MSIS-ICM criteria (77 % vs. 52 %; p = 0.02 ), and 2021 EBJIS criteria (87 % vs. 65 %; p = 0.02 ). Ultrasound-guided aspiration was more specific than fluoroscopy in diagnosing PJI using 2021 EBJIS criteria (100 % vs. 96 %; p = 0.001 ). Conclusions: ultrasound-guided aspiration is more frequently successful and yields more fluid than fluoroscopic-guided aspiration of THA. Ultrasound-guided aspiration is more sensitive in diagnosing PJI than fluoroscopy using culture data, 2018 MSIS-ICM criteria, and 2021 EBJIS criteria.

Ultrasound evaluations and guided procedures of the painful joint arthroplasty

The purpose of this article is to describe the use of ultrasound for the diagnosis and treatment of painful joint arthroplasty. Ultrasound plays a crucial role in the diagnosis of the painful joint arthroplasty, especially given its unique dynamic capabilities, convenience, and high resolution. Ultrasound guidance is also instrumental for procedures in both diagnosing and in select cases, treating the painful joint arthroplasty. Topics to be discussed in this article include trends in arthroplasty placement, benefits of the use of ultrasound overall, and ultrasound evaluation of periprosthetic joint infections. We will also review the sonographic findings with dissociated/displaced components and adverse reaction to metallic debris including metallosis, trunnionosis, and metal-on-metal pseudotumors. Additionally, we will discuss ultrasound evaluation of tendon pathologies with arthroplasties, including dynamic maneuvers to evaluate for tendon impingement/snapping. Finally, we will cover ultrasound-guided joint arthroplasty injection indications and precautions. KEY POINTS: • Ultrasound is preferred over MRI in patients with joint arthroplasty and plays a crucial role in diagnosis, especially given its unique dynamic capabilities, convenience and high resolution. • It is especially beneficial for US-guided aspiration in periprosthetic joint infections; effectively used to evaluate periprosthetic fluid collections, facilitating differentiation between abscesses and aseptic collections, and tracking sinus tracts. • Recently, the diagnosis of periprosthetic joint infections has shifted focus to biomarkers in the periprosthetic fluid, specifically α-defensin, which has a high sensitivity and specificity for diagnosing infection. • Cutibacterium acnes is a major pathogen responsible for shoulder arthroplasty infections, often presenting with normal laboratory values and since slow growing, must be kept for a minimum of 14 days.

Value of ultrasound-guided aspiration of hip arthroplasties performed in an orthopedic clinic by orthopedic surgeons

Background: Total joint arthroplasties continue to increase as do periprosthetic joint infections (PJIs). Ultrasound-guided aspiration can yield useful synovial fluid for analysis while avoiding radiation exposure. This study presents a high-yield, ultrasound-guided technique with analysis of aspiration results. Methods: All consecutive ultrasound-guided aspirations of hip arthroplasties performed from May 2016 through to April 2019 were retrospectively reviewed. Patient demographic information, component specifics, presence of draining sinus, and inflammatory markers were recorded. Results of aspiration including volume, appearance, lavage use, synovial fluid differential leukocyte count, synovial neutrophil percent, and culture results were recorded. Surgical results, specimen cultures, and surgeon description of purulence were recorded. Aspiration results were compared to the surgical specimen results in all patients who underwent reoperations. Results: Review of 349 hip aspirations demonstrated accuracy of 87 %, sensitivity of 83 %, specificity of 89 %, positive predictive value of 79 %, and negative predictive value 91 %. Surgical and aspiration cultures matched in 81 % of cases. Bloody aspirates and aspirates obtained after lavage had less accuracy at 69 % and 60 %, respectively. Specificity was 100 % for cultures obtained with lavage and 91 % for bloody aspirates. Synovial leukocyte count and neutrophil percentage was obtained in 85 % of aspirations, and cultures were obtained in 98 % of aspirates. Contamination rate was 2 %. Conclusion: Ultrasound-guided aspirations aid in the diagnosis of PJI. The use of lavage to obtain fluid is helpful when aspiration cultures are positive. Bloody aspirates are less accurate but have high specificity. A low contamination rate and 88 % accuracy results with this meticulous technique.

In Vitro and In Vivo Evaluation of 99mTc-Polymyxin B for Specific Targeting of Gram-Bacteria

Background: Infectious diseases are one of the main causes of morbidity and mortality worldwide. Nuclear molecular imaging would be of great help to non-invasively discriminate between septic and sterile inflammation through available radiopharmaceuticals, as none is currently available for clinical practice. Here, we describe the radiolabeling procedure and in vitro and in vivo studies of ^99mTc-polymyxin B sulfate (PMB) as a new single photon emission imaging agent for the characterization of infections due to Gram-negative bacteria. Results: Labeling efficiency was 97 ± 2% with an average molar activity of 29.5 ± 0.6 MBq/nmol. The product was highly stable in saline and serum up to 6 h. In vitro binding assay showed significant displaceable binding to Gram-negative bacteria but not to Gram-positive controls. In mice, ^99mTc-HYNIC-PMB was mainly taken up by liver and kidneys. Targeting studies confirmed the specificity of ^99mTc-HYNIC-PMB obtained in vitro, showing significantly higher T/B ratios for Gram-negative bacteria than Gram-positive controls. Conclusions: In vitro and in vivo results suggest that ^99mTc-HYNIC-PMB has a potential for in vivo identification of Gram-negative bacteria in patients with infections of unknown etiology. However, further investigations are needed to deeply understand the mechanism of action and behavior of ^99mTc-HYNIC-PMB in other animal models and in humans.

Anatomic Landmark-Guided Hip Aspiration in the Diagnosis of Periprosthetic Joint Infection

Hip aspirations used to detect a periprosthetic joint infection (PJI) are usually performed under fluoroscopy or ultrasound. The aim of this study was to evaluate the results of simply using anatomic landmarks for aspiration and detecting PJI without the use of any complicated technologies. The authors retrospectively reviewed a total of 186 consecutive hip aspirations performed between April 2015 and December 2018. All patients were suspected to have infections after total hip arthroplasty. The procedures were performed with the patients in the supine position. The authors aimed to aspirate at the neck of the prosthesis. They located the y-axis of the puncture point approximately 2 to 3 cm lateral to the pulse of the femoral artery in the region of the inguinal ligament. The x-axis was estimated by using the pubic symphysis or greater trochanter according to an anteroposterior radiograph of the hip joint. The aspiration failure rate, incidence of complications, and culture results were recorded. The overall aspiration failure rate was 3.8% (7 of 186). No obvious complications related to aspiration were observed. The saline lavage and reaspiration rate was 45.3% (81 of 179) due to "dry taps." The sensitivity, specificity, positive predictive value, and negative predictive value of the remaining 169 patients with definite diagnoses were 0.781 (95% CI, 0.678-0.860), 0.939 (95% CI, 0.857-0.977), 0.931 (95% CI, 0.841-0.975), and 0.802 (95% CI, 0.706-0.874), respectively. Anatomic landmark-guided hip aspiration was a convenient method that could provide satisfactory detection of PJI. [Orthopedics. 2021;44(1):e85-e90.].

Saline lavage after a "dry tap"

AIMS

In patients with a "dry" aspiration during the investigation of prosthetic joint infection (PJI), saline lavage is commonly used to obtain a sample for analysis. The aim of this study was to investigate prospectively the impact of saline lavage on synovial fluid analysis in revision arthroplasty.

METHODS

Patients undergoing revision hip (THA) or knee arthroplasty (TKA) for any septic or aseptic indication were enrolled. Intraoperatively, prior to arthrotomy, the maximum amount of fluid possible was aspirated to simulate a dry tap (pre-lavage) followed by the injection with 20 ml of normal saline and re-aspiration (post-lavage). Pre- and post-lavage synovial white blood cell (WBC) count, percent polymorphonuclear cells (%PMN), and cultures were compared.

RESULTS

A total of 78 patients had data available for analysis; 17 underwent revision THA and 61 underwent revision TKA. A total of 16 patients met modified Musculoskeletal Infection Society (MSIS) criteria for PJI. Pre- and post-lavage %PMNs were similar in septic patients (87% vs 85%) and aseptic patients (35% vs 39%). Pre- and post-lavage synovial fluid WBC count were far more disparate in septic (53,553 vs 8,275 WBCs) and aseptic (1,103 vs 268 WBCs) cohorts. At a cutoff of 80% PMN, the post-lavage aspirate had a sensitivity of 75% and specificity of 95%. At a cutoff of 3,000 WBCs, the post-lavage aspirate had a sensitivity of 63% and specificity of 98%. As the post-lavage synovial WBC count increased, the difference between pre- and post-lavage %PMN decreased (mean difference of 5% PMN in WBC < 3,000 vs mean difference 2% PMN in WBC > 3,000, p = 0.013). Of ten positive pre-lavage fluid cultures, only six remained positive post-lavage.

CONCLUSION

While saline lavage aspiration significantly lowered the synovial WBC count, the %PMN remained similar, particularly at WBC counts of > 3,000. These findings suggest that in patients with a dry-tap, the %PMN of a saline lavage aspiration has reasonable sensitivity (75%) for the detection of PJI. Cite this article: Bone Joint J 2020;102-B(6 Supple A):138-144.

Value of multidetector computed tomography for the differentiation of delayed aseptic and septic complications after total hip arthroplasty

OBJECTIVE

The differentiation between delayed aseptic and septic complications of total hip arthroplasty is crucial to allow appropriate surgical planning and timely antimicrobial treatment. The aim of this study was to investigate the utility of multidetector computed tomography (CT) findings to diagnose aseptic mechanical loosening, granulomatous reaction, and periprosthetic joint infection in patients who underwent total hip arthroplasty before revision surgery.

MATERIALS AND METHODS

Ninety-six consecutive patients with a clinical suspicion of periprosthetic complications underwent revision surgery over an 8-year period. All patients had been evaluated preoperatively using multidetector CT without contrast media. Two blinded musculoskeletal radiologists reviewed multidetector CT images, including periprosthetic soft-tissue accumulation, prosthetic acetabular malposition, periprosthetic osteolysis, enlarged iliac lymph nodes, and heterotopic ossification. Risk factors for aseptic and septic loosening were identified using multivariate analysis.

RESULTS

Multidetector CT-related variables independently associated with periprosthetic joint infection were high periprosthetic soft-tissue accumulation, periprosthetic osteolysis without expansile periosteal reaction and enlarged iliac lymph nodes. On the other hand, the absence of the following radiological signs: low or high periprosthetic soft-tissue accumulation, mild or severe periprosthetic osteolysis, and enlarged iliac lymph nodes, were predictors of aseptic mechanical loosening. Low periprosthetic soft-tissue accumulation, severe periprosthetic osteolysis with expansile periosteal reaction, and mild acetabular malposition were significant variables associated with granulomatosis.

CONCLUSION

Multidetector CT findings are useful to differentiate between aseptic and septic complications before revision surgery. The presence of osteolysis with expansile periosteal reaction appeared to be a time-dependent variable.

Accuracy of Computed Tomography-Guided Joint Aspiration and Computed Tomography Findings for Prediction of Infected Hip Prosthesis

BACKGROUND

Infection after total hip arthroplasty remains a diagnostic challenge. We assessed the accuracy of computed tomography (CT)-guided joint aspiration combined with CT findings for prediction of septic hip prosthesis before revision surgery.

METHODS

A total of 96 patients (64.6% men; mean age, 68 years) scheduled for elective revision surgery due to suspicion of infection after total hip arthroplasty underwent CT-guided joint aspiration. Volume and microbiological cultures of aspirated fluid and salient findings on CT scans, including periprosthetic soft-tissue mass, malpositioning of the prosthesis, periprosthetic osteolysis, reactive enlarged lymph nodes, and heterotopic ossification, were assessed by a blinded radiologist.

RESULTS

Septic hip prosthesis was shown on revision surgery in 35 patients (36.4%), with Staphylococcus epidermidis isolated in 54.3% of cases. Culture of the aspirated fluid yielded the same microorganism in 24 patients (68.6%). The accuracy of preoperative CT-guided joint aspiration was 86.5%. High volume (>1 mL) of aspirated fluid was recorded in 32 patients (33.3%). In the multivariate analysis, high volume on CT aspiration, accumulation of soft tissue exceeding the joint margin, osteolysis without bone insufflation, and enlarged iliac lymph nodes were significant predictors of infected hip prosthesis. Similar results were obtained after adjustment of the model by the presence of aggressive granulomatosis.

CONCLUSION

Preoperative CT-guided joint aspiration is accurate to diagnose septic hip prosthesis based on CT imaging findings and volume and bacterial culture of the aspirated fluid. Enlarged iliac lymph nodes emerged as a strong predictor of infection.

Diagnosis of peripheral bone and prosthetic joint infections: overview on the consensus documents by the EANM, EBJIS, and ESR (with ESCMID endorsement)

OBJECTIVES

Peripheral bone infection (PBI) and prosthetic joint infection (PJI) are two different infectious conditions of the musculoskeletal system. They have in common to be quite challenging to be diagnosed and no clear diagnostic flowchart has been established. Thus, a conjoined initiative on these two topics has been initiated by the European Society of Radiology (ESR), the European Association of Nuclear Medicine (EANM), the European Bone and Joint Infection Society (EBJIS), and the European Society of Clinical Microbiology and Infectious Diseases (ESCMID). The purpose of this work is to provide an overview on the two consensus documents on PBI and PJI that originated by the conjoined work of the ESR, EANM, and EBJIS (with ESCMID endorsement).

METHODS AND RESULTS

After literature search, a list of 18 statements for PBI and 25 statements for PJI were drafted in consensus on the most debated diagnostic challenges on these two topics, with emphasis on imaging.

CONCLUSIONS

Overall, white blood cell scintigraphy and magnetic resonance imaging have individually demonstrated the highest diagnostic performance over other imaging modalities for the diagnosis of PBI and PJI. However, the choice of which advanced diagnostic modality to use first depends on several factors, such as the benefit for the patient, local experience of imaging specialists, costs, and availability. Since robust, comparative studies among most tests do not exist, the proposed flowcharts are based not only on existing literature but also on the opinion of multiple experts involved on these topics.

KEY POINTS

• For peripheral bone infection and prosthetic joint infection, white blood cell and magnetic resonance imaging have individually demonstrated the highest diagnostic performance over other imaging modalities. • Two evidence- and expert-based diagnostic flowcharts involving variable combination of laboratory tests, biopsy methods, and radiological and nuclear medicine imaging modalities are proposed by a multi-society expert panel. • Clinical application of these flowcharts depends on several factors, such as the benefit for the patient, local experience, costs, and availability.

Consensus document for the diagnosis of prosthetic joint infections: a joint paper by the EANM, EBJIS, and ESR (with ESCMID endorsement)

Background

For the diagnosis of prosthetic joint infection, real evidence-based guidelines to aid clinicians in choosing the most accurate diagnostic strategy are lacking.

Aim and Methods

To address this need, we performed a multidisciplinary systematic review of relevant nuclear medicine, radiological, orthopaedic, infectious, and microbiological literature to define the diagnostic accuracy of each diagnostic technique and to address and provide evidence-based answers on uniform statements for each topic that was found to be important to develop a commonly agreed upon diagnostic flowchart.

Results and Conclusion

The approach used to prepare this set of multidisciplinary guidelines was to define statements of interest and follow the procedure indicated by the Oxford Centre for Evidence-based Medicine (OCEBM).

Electronic supplementary material

The online version of this article (10.1007/s00259-019-4263-9) contains supplementary material, which is available to authorized users.

Ultrasonography as a Diagnostic, Therapeutic, and Research Tool in Orthopaedic Surgery

Ultrasonography is an imaging modality that facilitates the diagnosis of pathology and injection therapy without exposing the patient to radiation. In addition, ultrasonography has become popular because of its portability, low cost, and production of real-time tomographic images that provide a cross-sectional view of anatomic structures. Despite its benefits and widespread adoption in general medicine and other specialties, however, ultrasonography is not as well adapted as a diagnostic and research tool in orthopaedic surgery. An understanding of the basic principles of ultrasonography and the evidence supporting its use can aid the orthopaedic surgeon in applying this modality appropriately in clinical practice.

Osteoclasts in Periprosthetic Osteolysis: The Charnley Arthroplasty Revisited

BACKGROUND

Periprosthetic osteolysis by polyethylene wear debris-triggered osteoclasts is viewed as the main pathophysiological pathway in aseptic loosening in total hip arthroplasty. The present aim was to study osteoclast occurrence in osteolytic lesions in early and late revisions of the Charnley low-friction torque arthroplasty (CLFA).

METHODS

Biopsies of the soft interface membrane and the adjacent bone were taken from osteolytic lesions during revision of 16 loose CLFA, early (2-6 years) or late (>10 years) after primary surgery. By light microscopy (LM), cell-dense regions with signs of osteoclast-mediated bone resorption were selected for transmission electron microscopy. Three additional patients were studied in LM for osteoclast markers (tartrate-resistant acid phosphatase and Cathepsin K).

RESULTS

LM disclosed a low-grade chronic inflammation and birefringent particles in most sections. Multiple conglomerates of tartrate-resistant acid phosphatase positive and Cathepsin K positive mononuclear and multinucleated cells were found deep in the fibrous interface membrane. Transmission electron microscopy showed traces of polyethylene-like particles in 67%-100% of the cells. Osteoclast-like cells exhibiting resorptive activity were few (mean, 0.7%; standard deviation, 0.2%), and multinucleated cells, possibly osteoclast precursor cells, located immediately on the bone were also scarce (mean, 2.7%; standard deviation, 5.3%). Multinucleated (odds ratio, 3.0; 95% confidence interval, 1.7-5.5) and macrophage-like cells (odds ratio, 3.6; 95% confidence interval, 2.2-5.6) were typically located deeper in the inflammatory interface membrane with a pathologic appearance with distension and abundance of phagocytic vacuoles. There were no systematic differences in cell populations between early or late revisions.

CONCLUSION

Despite probable ongoing osteoclastogenesis in the osteolytic lesions, there were few sites of osteoclast-mediated bone resorption. These findings attach a contributing biological explanation to the longevity of the CLFA.

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.

Preoperative aspiration culture for preoperative diagnosis of infection in total hip or knee arthroplasty

This meta-analysis evaluated preoperative aspiration culture for diagnosing prosthetic joint infection (PJI) in total hip arthroplasty (THA) and total knee arthroplasty (TKA). The pooled sensitivity and specificity were 0.72 (95% confidence interval, 0.65 to 0.78) and 0.95 (0.93 to 0.97), respectively. Subgroup analyses revealed nonsignificant worse diagnostic performance for THA than for TKA (sensitivity, 0.70 versus 0.78; specificity, 0.94 versus 0.96). Preoperative aspiration culture has moderate to high sensitivity and very high specificity for diagnosing PJI.

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

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

Accuracy of CT-guided joint aspiration in patients with suspected infection status post-total hip arthroplasty

OBJECTIVE

To determine the accuracy of guided computed tomography aspiration in the detection of septic hip prosthesis before surgery.

MATERIALS AND METHODS

Sixty-three patients (35 women and 28 men; age range, 29-86 years; mean age, 71 years) with clinically suspected septic hip prosthesis were prospectively studied with independent review board (IRB) approval. Volume and microbiological cultures of aspirated fluid and several computed tomography imaging findings such as periprosthetic fluid collections, prosthetic acetabular malposition, and heterotopic ossification were analyzed. All patients underwent revision surgery and infection was finally diagnosed in 33 patients.

RESULTS

Statistical comparative analysis was performed comparing computed tomography aspiration and surgical findings (95% CI; level of significance at P=0.05 two-sided) with 70% sensitivity, 100% specificity, 84% accuracy, 100% positive predictive value, and 75% negative predictive value. Using Fisher's exact test, the presence of periprosthetic fluid collections (P=0.001), prosthetic acetabular malposition (P=0.025) and aspirated fluid volume (P=0.009) were significantly higher in infected than in non-infected prostheses, whereas heterotopic ossification was not (P=0.429).

CONCLUSION

Computed tomography aspiration is accurate to preoperatively diagnose septic hip prosthesis on the basis of volume and bacterial cultures of aspirated joint fluid. Furthermore, imaging findings such as periprosthetic fluid collections and prosthetic acetabular malposition strongly suggest infected prosthesis.

Diagnosis of periprosthetic joint infections of the hip and knee

No preferred test for diagnosis of periprosthetic joint infection exists, and the algorithm for the workup of patients suspected of infection remains unclear. The work group evaluated the available literature to determine the role of each diagnostic modality and devise a practical algorithm that allows physicians to reach diagnosis of periprosthetic joint infection. Ten of the 15 recommendations have strong or moderate evidence in support. These include matters involving erythrocyte sedimentation rate and C-reactive protein level testing, knee and hip aspiration, and stopping the use of antibiotics prior to obtaining intra-articular cultures. The group recommends against the use of intraoperative Gram stain but does recommend the use of frozen sections of peri-implant tissues in reoperation patients in whom infection has not been established, as well as multiple cultures in reoperation patients being assessed for infection. The group recommends against initiating antibiotic treatment in patients with suspected infection until after joint cultures have been obtained, but recommends that prophylactic preoperative antibiotics not be withheld in patients at lower probability for infection.

[CT evaluation of total HIP prosthesis infection]

PURPOSE

To evaluate the ability of CT imaging to detect infectious lesions in total hip prosthesis.

PATIENTS AND METHODS

CT was performed in 17 cases of suspected total hip prosthesis infection. Images were reviewed to evaluate for the presence of soft tissue abscess, hip joint effusion or fistula and peri-prosthetic lucency or erosion at bone window setting. The feasibility of CT imaging is assessed with regards to metallic artifacts.

RESULTS

Infection was confirmed in 10 hips. A soft tissue abscess was present in 8 of these cases, in association to a joint effusion, presumably septic, in 7 cases. A fistula was identified in 8 cases. A peri-prosthetic lucency was present in 10 cases, 7 of which with infection, and erosions were noted in 4 patients, 2 of which with infection. Metallic artifacts reduced image quality but did not prevent detection of soft tissue abscesses.

CONCLUSION

CT is useful for detection of soft tissue abscesses in patients with infected hip prosthesis. CT is useful for surgical planning or follow-up of patients treated conservatively.

Backgrounds of antibiotic-loaded bone cement and prosthesis-related infection

Antibiotic-loaded bone cement has been in use for over 30 years for the fixation of total joint arthroplasties, although its mechanism of action is still poorly understood. This review presents the backgrounds of bone cements, prosthesis-related infection and antibiotic-loaded bone cements. It is shown that antibiotic-loaded bone cement has a significant effect on bacteria, particularly in animal and clinical studies. However, recently, antimicrobial resistance among bacteria has been ascribed to the antibiotic-loaded bone cement. The unresolved issues both regarding the action of antibiotic-loaded bone cement and the nature of the antimicrobial resistance necessitate further research into the interaction of antibiotic-loaded bone cement and bacteria.

Periprosthetic sepsis

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