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

ACR Appropriateness Criteria® Imaging After Total Knee Arthroplasty: 2023 Update

Total knee arthroplasty is the most commonly performed joint replacement procedure in the United States. This manuscript will discuss the recommended imaging modalities for six clinical variants; 1. follow-up of symptomatic or asymptomatic patients with a total knee arthroplasty. Initial imaging, 2. Suspected infection after total knee arthroplasty. Additional imaging following radiographs, 3. Pain after total knee arthroplasty. Infection excluded. Suspect aseptic loosening or osteolysis or instability. Additional imaging following radiographs, 4. Pain after total knee arthroplasty. Suspect periprosthetic or hardware fracture. Additional imaging following radiographs, 5. Pain after total knee arthroplasty. Measuring component rotation. Additional imaging following radiographs, and 6. Pain after total knee arthroplasty. Suspect periprosthetic soft-tissue abnormality unrelated to infection, including quadriceps or patellar tendinopathy. Additional imaging following radiographs. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

ACR Appropriateness Criteria® Imaging After Total Hip Arthroplasty

This article reviews evidence for performing various imaging studies in patients with total hip prostheses. Routine follow-up is generally performed with radiography. Radiographs are also usually the initial imaging modality for patients with symptoms related to the prosthesis. Following acute injury with pain, noncontrast CT may add information to radiographic examination regarding the presence and location of a fracture, component stability, and bone stock. Image-guided joint aspiration, noncontrast MRI, and white blood cell scan and sulfur colloid scan of the hip, are usually appropriate studies for patients suspected of having periprosthetic infection. For evaluation of component loosening, wear, and/or osteolysis, noncontrast CT or MRI are usually appropriate studies. Noncontrast MRI is usually appropriate for identifying adverse reaction to metal debris related to metal-on-metal articulations. For assessing patients after hip arthroplasty, who have trochanteric pain and nondiagnostic radiographs, ultrasound, or MRI are usually appropriate studies. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Molecular Imaging of Periprosthetic Joint Infections

Infection is an infrequent complication of lower extremity prosthetic joint surgery. Approximately one third develop within 3 months (early), another third within 1 year (delayed), and the remainder more than 1 year (late) after surgery. The diagnosis of periprosthetic joint infection is not always straightforward. Pain, the most common symptom, is present in 90%-100% of patients. The presence of fever is more variable, ranging from less than 5% to more than 40% of patients with infection. Erythema and joint swelling are often present in acute infections, but are less common in chronic infections. Erythrocyte sedimentation rate, C-reactive protein and interleukin-6 levels are useful "rule out" tests, while peripheral blood leukocyte count and serum tumor necrosis factor α are not helpful. The diagnosis of periprosthetic joint infection often requires a combination of blood, synovial fluid, and tissue sample tests, as well as imaging. Plain radiographs lack sensitivity and specificity. Molecular imaging is useful for evaluating painful joint replacements. Bone scintigraphy is most useful as a screening test. If it is negative then infection and aseptic loosening are unlikely. Combined labeled leukocyte/bone marrow imaging is a very specific test for diagnosing lower extremity joint arthroplasty infection; sensitivity is more variable. Despite more than two decades of investigation, there still is no consensus on the value of ¹⁸F-FDG for diagnosing periprosthetic joint infection. Differing test probabilities, an inability to discriminate between infection and inflammation secondary to physiologic reactions, and lack of standardized interpretative criteria are obstacles to incorporating ¹⁸F-FDG into the routine diagnostic imaging workup of periprosthetic joint infection. Preliminary results for gallium-68 citrate, fluorine-18, and technetium-99m labeled antimicrobial fragments are encouraging but no large scale trials with these agents have been conducted. Limited data suggest that labeled leukocyte/bone marrow SPECT/CT and ¹⁸F-FDG-PET/CT are specific but not sensitive for diagnosing periprosthetic infection of shoulder arthroplasties. There are minimal data on molecular imaging for monitoring treatment response in periprosthetic infections.

Nuclear Medicine Scans in Total Joint Replacement

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A 3-phase bone scan is a potential first-line nuclear medicine study for pain after total joint arthroplasty (TJA) when there is concern for periprosthetic joint infection or aseptic loosening.

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In patients who have a positive bone scintigraphy result and suspected infection of the joint, but where aspiration or other studies are inconclusive, labeled leukocyte scintigraphy with bone marrow imaging may be of benefit.

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Magnetic resonance imaging (MRI), while not a nuclear medicine study, also shows promise and has the advantage of providing information about the soft tissues around a total joint replacement.

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Radiotracer uptake patterns in scintigraphy are affected by the prosthesis (total knee arthroplasty [TKA] versus total hip arthroplasty [THA]) and the use of cement.

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Nuclear medicine scans may be ordered 1 year postoperatively but may have positive findings that are due to normal physiologic bone remodeling. Nuclear studies may be falsely positive for up to 2 years after TJA.

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Single-photon emission computed tomography (SPECT) combined with computed tomography (CT) (SPECT/CT), fluorine-18 fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/CT, and MRI show promise; however, more studies are needed to better define their role in the diagnostic workup of pain after TJA.

Handling of Doubtful WBC Scintigraphies in Patients with Suspected Prosthetic Joint Infections

Despite the application of EANM recommendations for radiolabelled white-blood-cells (WBC) scintigraphy, some cases still remain doubtful based only on visual analysis. The aim of this study was to investigate the role of semi-quantitative analysis and bone marrow scan (BMS) in solving doubtful cases. We retrospectively evaluated all [^99mTc]HMPAO-WBC scintigraphies performed, in the last 7 years, for a suspected monolateral prosthetic joint infection (PJI). In doubtful cases, we used five different thresholds of increase of target-to-background (T/B) ratio, between delayed and late images, as criteria of positivity (5%, 10%, 15%, 20% and 30%). BMS were also analysed and sensitivity, specificity and accuracy of different methods were calculated according to final diagnosis. The sensitivity, specificity and accuracy were, respectively, 77.8%, 43.8% and 53.0% for the cut-off at 5%; 72.2%, 66.7% and 68.2% for the cut-off at 10%; 66.7%, 75.0% and 72.7% for the cut-off at 15%; 66.7%, 85.4% and 80.3% for the cut-off at 20%; 33.3%, 93.8% and 77.3% for the cut-off at 30%. BMS provided a significantly higher diagnostic performance than 5%, 10% and 15% thresholds. Conversely, we did not observe any statistically significant difference between BMS and the cut-off of more than 20%. Therefore, doubtful cases should be analysed semi-quantitatively. An increase in T/B ratio of more than 20% between delayed and late images, should be considered as a criterion of positivity, thus avoiding BMS.

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.

ACR Appropriateness Criteria® Imaging After Total Knee Arthroplasty

Total knee arthroplasty (TKA) is the most commonly performed joint replacement procedure in the United States and annual demand for primary TKA is expected to grow by 673% by 2030. The first part provides an overview of imaging modalities (radiographs, CT, MRI, ultrasound, and various nuclear medicine studies) and discusses their usefulness in the imaging evaluation of TKA. The second part focuses on evidence-based imaging and imaging-guided intervention algorithms for the workup of TKA and its complications, including routine follow-up, component wear, periprosthetic infection, aseptic loosening, granulomas/osteolysis, conventional and rotational instability, periprosthetic fracture, patellar complications, and a variety of periprosthetic soft tissue abnormalities. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Role of Nuclear Medicine for Diagnosing Infection of Recently Implanted Lower Extremity Arthroplasties

Infection is an infrequent complication of lower extremity prosthetic joint surgery. Approximately one-third develop within 3 months (early), another third within 1 year (delayed), and the remainder more than 1 year (late) after surgery. Diagnosing prosthetic joint infection, especially in the early postoperative period during the first year, is challenging. Pain is almost always present. The presence of fever is variable, ranging from less than 5% to more than 40% of patients. Leukocytosis is a poor predictor of infection. After primary uncomplicated arthroplasty, the C-reactive protein remains elevated for up to 3 weeks. The erythrocyte sedimentation rate can remain elevated for up to 1 year. Although joint aspiration with culture, the definitive preoperative diagnostic procedure, is specific, its sensitivity is variable. Plain radiographs lack sensitivity and specificity. Radionuclide studies are useful for evaluating painful joint replacements, but data on their utility during the early postoperative period are limited. During the first year after arthroplasty insertion, the bone scan can exclude infection. It is a good "rule-out" test, but it is not reliable for "ruling in" infection. Gallium-67 accumulates in normally healing surgical incisions and in aseptic inflammation. With an accuracy of 60%-80% for diagnosing prosthetic joint infection, there is little role for this radiopharmaceutical for evaluating prosthetic joints, regardless of age. Although data about diagnosing prosthetic joint infection with ¹⁸F-FDG in the early postoperative period are lacking, uptake of this radiopharmaceutical in a variety of postoperative settings for variable time periods is well known. Furthermore, its utility for diagnosing prosthetic joint infection in general, after nearly 2 decades of investigation, remains to be established. Indium-111-labeled leukocytes do not accumulate in normally healing surgical wounds, and in combination with marrow imaging, the test is about 90% accurate for diagnosing prosthetic joint infection. Preliminary data indicate a comparable accuracy in the early postoperative period.

White cell and marrow imaging: subtracting uncertainty

A subtraction method for assessments of dual-isotope indium-111 (In)-labelled white cell and Tc-nanocoll was proposed, and following a pilot study was introduced in routine service to improve the confidence of reporters. This technical note describes a simple technique to produce subtraction images from routinely acquired images to investigate and exclude post joint replacement infection. Labelled leucocytes (with In) show areas of increased white cell accumulation, whereas Tc-nanocoll images show bone marrow distribution. Images resulting from the subtraction protocol highlight any areas of white cell activity which is not concurrent with the marrow distribution indicative of infection. Fusion images produced from these images sets also assists in localization of white cell accumulation(s). Key to the success of this technique is the use of simultaneous acquisition of both white cell and marrow images; thus removing any issues with patient movement and/or repositioning. Reporting clinicians convey a clear preference for the inclusion of the subtracted and fused images at clinical review.

Bone scan in painful knee arthroplasty: obsolete or actual examination?

ptic loosening, instability and infection are the major causes of TKA failure. For many years, nuclear medicine (NM) imaging was helpful to frame a painful total joint arthroplasty. The differentiation of septic from aseptic prosthetic loosening is critical. The latest AAOS guidelines to detect periprosthetic joint infection (PJI) restrict the role of NM scintigraphy. On the other hand, several studies suggest that NM imaging plays an important role in the evaluation of patients with painful prosthesis, but its specificity in differentiating aseptic loosening from infection is low. Moreover, scintigraphic exams showed different diagnostic accuracy in TKA compared to total hip arthroplasty (THA).

PURPOSE

To assess and discuss current knowledges about the diagnostic value of the various scans in TKA failure alone.

METHODS

We perform a pubmed/medline search to identify all papers published in the literature matching the following key words: "total knee arthroplasty", "bone", "scintigraphy", "imaging", "three-phase", "triple-phase", "99mTc-HDP", "99mTc-MDP", "99mTc-hydroxymethane diphosphonate", and "99m Tc-methylenediphosphonate", "leukocyte scanning", "labeled leukocyte scintigraphy", "antigranulocyte", "nuclear medicine", "septic loosening", "aseptic loosening" and "infection".

RESULTS

Three phases bone scintigraphy results an early diagnostic screening test or part of the preoperative tests for painful TKA and when PJI is suspected. Instead, leukocyte/bone marrow scintigraphy is superior to other scintigraphic tools in diagnosis of TKA infections. Granulocyte scintigraphy, seems to be an excellent choice when the diagnosis is unclear. Moreover, nuclear diagnostic tests showed different diagnostic accuracy between TKA and THA.

CONCLUSIONS

Although nuclear diagnostic tests for THA failure are superior in  diagnostic accuracy compared to TKA, NM scintigraphy is still an effective tool in the identification of chronic, low grade PJI. To date, scintigraphic exams have an higher levels of sensitivity, specificity and accuracy. Currently, leukocyte/bone marrow scintigraphy is considered the gold standard for this aim.  Nevertheless, further studies are needed to assess and improve the accuracy of the scintigraphic exams in order to discriminate the causes of failure for painful TKA.

What is the Accuracy of Nuclear Imaging in the Assessment of Periprosthetic Knee Infection? A Meta-analysis

BACKGROUND

In the assessment of possible periprosthetic knee infection, various imaging modalities are used without consensus regarding the most accurate technique.

QUESTIONS/PURPOSES

To perform a meta-analysis to compare the accuracy of various applied imaging modalities in the assessment of periprosthetic knee infection.

METHODS

A systematic review and meta-analysis was conducted with a comprehensive search of MEDLINE and Embase^® in accordance with the PRISMA and Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) recommendations to identify clinical studies in which periprosthetic knee infection was investigated with different imaging modalities. The sensitivity and specificity of each imaging technique were determined and compared with the results of microbiologic and histologic analyses, intraoperative findings, and clinical followup of more than 6 months. A total of 23 studies, published between 1990 and 2015, were included for meta-analysis, representing 1027 diagnostic images of symptomatic knee prostheses. Quality of the included studies showed low concerns regarding external validity, whereas internal validity indicated more concerns regarding the risk of bias. The most important concerns were found in the lack of uniform criteria for the diagnosis of a periprosthetic infection and the flow and timing of the included studies. Differences among techniques were tested at a probability less than 0.05 level. Where there was slight overlap of confidence intervals for two means, it is possible for the point estimates to be statistically different from one another at a probability less than 0.05. The z-test was used to statistically analyze differences in these situations.

RESULTS

Bone scintigraphy was less specific than all other modalities tested (56%; 95% CI, 0.47-0.64; p < 0.001), and leukocyte scintigraphy (77%; 95% CI, 0.69-0.85) was less specific than antigranulocyte scintigraphy (95%; 95% CI, 0.88-0.98; p < 0.001) or combined leukocyte and bone marrow scintigraphy (93%; 95% CI, 0.86-0.97; p < 0.001). Fluorodeoxyglucose positron emission tomography (FDG-PET) (84%; 95% CI, 0.76-0.90) was more specific than bone scintigraphy (56%; 95% CI, 0.47-0.64; p < 0.001), and less specific than antigranulocyte scintigraphy (95%; 95% CI, 0.88-0.98; p = 0.02) and combined leukocyte and bone marrow scintigraphy (93%; 95% CI, 0.86-0.97; p < 0.001). Leukocyte scintigraphy (88%; 95% CI, 0.81-0.93; p = 0.01) and antigranulocyte scintigraphy (90%; 95% CI, 0.78-0.96; p = 0.02) were more sensitive than FGD-PET (70%; 95% CI, 0.56-0.81). However, because of broad overlapping of confidence intervals, no differences in sensitivity were observed among the other modalities, including combined bone scintigraphy (93%; 95% CI, 0.85-0.98) or combined leukocyte and bone marrow scintigraphy (80%; 95% CI, 0.66-0.91; p > 0.05 for all paired comparisons).

CONCLUSIONS

Based on current evidence, antigranulocyte scintigraphy and combined leukocyte and bone marrow scintigraphy appear to be highly specific imaging modalities in confirming periprosthetic knee infection. Bone scintigraphy was a highly sensitive imaging technique but lacks the specificity needed to differentiate among various conditions that cause painful knee prostheses. FDG-PET may not be the preferred imaging modality because it is more expensive and not more effective in confirming periprosthetic knee infection.

LEVEL OF EVIDENCE

Level III, diagnostic study.

The Accuracy of Imaging Techniques in the Assessment of Periprosthetic Hip Infection: A Systematic Review and Meta-Analysis

BACKGROUND

Various imaging techniques are used for excluding or confirming periprosthetic hip infection, but there is no consensus regarding the most accurate technique. The objective of this study was to determine the accuracy of current imaging modalities in diagnosing periprosthetic hip infection.

METHODS

A systematic review and meta-analysis of the literature was conducted with a comprehensive search of MEDLINE and Embase to identify clinical studies in which periprosthetic hip infection was investigated with different imaging modalities. The sensitivity and specificity of each imaging technique were determined and compared with the results of microbiological and histological analysis, intraoperative findings, and clinical follow-up of >6 months.

RESULTS

A total of 31 studies, published between 1988 and 2014, were included for meta-analysis, representing 1,753 hip prostheses. Quality assessment of the included studies identified low concerns with regard to external validity but more concerns with regard to internal validity including risk of bias (>50% of studies had insufficient information). No meta-analysis was performed for radiography, ultrasonography, computed tomography, and magnetic resonance imaging because of insufficient available clinical data. The pooled sensitivity and specificity were 88% (95% confidence interval [CI], 81% to 94%) and 92% (95% CI, 88% to 96%), respectively, for leukocyte scintigraphy; 86% (95% CI, 80% to 90%) and 93% (95% CI, 90% to 95%) for fluorodeoxyglucose positron emission tomography (FDG PET); 69% (95% CI, 58% to 79%) and 96% (95% CI, 93% to 98%) for combined leukocyte and bone marrow scintigraphy; 84% (95% CI, 70% to 93%) and 75% (95% CI, 66% to 82%) for antigranulocyte scintigraphy; and 80% (95% CI, 72% to 86%) and 69% (95% CI, 64% to 73%) for bone scintigraphy.

CONCLUSIONS

Of the currently used imaging techniques, leukocyte scintigraphy has satisfactory accuracy in confirming or excluding periprosthetic hip infection. Although not significantly different, combined leukocyte and bone marrow scintigraphy was the most specific imaging technique. FDG PET has an appropriate accuracy in confirming or excluding periprosthetic hip infection, but may not yet be the preferred imaging modality because of limited availability and relatively higher cost.

LEVEL OF EVIDENCE

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

Assessment of Therapy Response by FDG PET in Infection and Inflammation

Positron emission tomography (PET) is a well-known imaging modality in assessing the treatment response to chemotherapy or radiotherapy in various malignancies. A systematic review of the literature reveals a few publications reporting evaluation of the treatment response in benign conditions using PET/computed tomography. PET holds a promising future role in the follow-up of inflammatory or infectious diseases. In this article, [(18)F]Fluorodeoxyglucose PET as a tool in the evaluation, treatment, and follow-up of infectious and inflammatory diseases is discussed.

Radionuclide imaging of osteomyelitis

Radionuclide procedures frequently are performed as part of the diagnostic workup of osteomyelitis. Bone scintigraphy accurately diagnoses osteomyelitis in bones not affected by underlying conditions. Degenerative joint disease, fracture, and orthopedic hardware decrease the specificity of the bone scan, making it less useful in these situations. Gallium-67 scintigraphy was often used as an adjunct to bone scintigraphy for diagnosing osteomyelitis. However, now it is used primarily for spinal infections when (18)F-FDG imaging cannot be performed. Except for the spine, in vitro-labeled leukocyte imaging is the nuclear medicine test of choice for diagnosing complicating osteomyelitis. Leukocytes accumulate in bone marrow as well as in infection. Performing complementary bone marrow imaging with (99m)Tc-sulfur colloid facilitates the differentiation between osteomyelitis and normal marrow and improves test overall accuracy. Antigranulocyte antibodies and antibody fragments, such as (99m)Tc-besilesomab and (99m)Tc-sulesomab, were developed to eliminate the disadvantages associated with in vitro-labeled leukocytes. These agents, however, have their own shortcomings and are not widely available. As biotin is used as a growth factor by certain bacteria, (111)In-biotin is useful to diagnose spinal infections. Radiolabeled synthetic fragments of ubiquicidin, a naturally occurring human antimicrobial peptide that targets bacteria, can differentiate infection from sterile inflammation and may be useful to monitor response to treatment. (18)F-FDG is extremely useful in the diagnostic workup of osteomyelitis. Sensitivity in excess of 95% and specificity ranging from 75%-99% have been reported. (18)F-FDG is the radionuclide test of choice for spinal infection. The test is sensitive, with a high negative predictive value, and reliably differentiates degenerative from infectious vertebral body end-plate abnormalities. Data on the accuracy of (18)F-FDG for diagnosing diabetic pedal osteomyelitis are contradictory, and its role for this indication remains to be determined. Initial investigations suggested that (18)F-FDG accurately diagnoses prosthetic joint infection; more recent data indicate that it cannot differentiate infection from other causes of prosthetic failure. Preliminary data on the PET agents gallium-68 and iodine-124 fialuridine indicate that these agents may have a role in diagnosing osteomyelitis.

Nuclear medicine and the failed joint replacement: Past, present, and future

Soon after the introduction of the modern prosthetic joint, it was recognized that radionuclide imaging provides useful information about these devices. The bone scan was used extensively to identify causes of prosthetic joint failure. It became apparent, however, that although sensitive, regardless of how the images were analyzed or how it was performed, the test was not specific and could not distinguish among the causes of prosthetic failure. Advances in anatomic imaging, notably cross sectional modalities, have facilitated the diagnosis of many, if not most, causes of prosthetic failure, with the important exception of infection. This has led to a shift in the diagnostic paradigm, in which nuclear medicine investigations increasingly have focused on diagnosing infection. The recognition that bone scintigraphy could not reliably diagnose infection led to the development of combined studies, first bone/gallium and subsequently leukocyte/bone and leukocyte/marrow imaging. Labeled leukocyte imaging, combined with bone marrow imaging is the most accurate (about 90%) imaging test for diagnosing joint arthroplasty infection. Its value not withstanding, there are significant disadvantages to this test. In-vivo techniques for labeling leukocytes, using antigranulocyte antibodies have been explored, but have their own limitations and the results have been inconsistent. Fluorodeoxyglucose (FDG)-positron emission tomography (FDG-PET) has been extensively investigated for more than a decade but its role in diagnosing the infected prosthesis has yet to be established. Antimicrobial peptides bind to bacterial cell membranes and are infection specific. Data suggest that these agents may be useful for diagnosing prosthetic joint infection, but large scale studies have yet to be undertaken. Although for many years nuclear medicine has focused on diagnosing prosthetic joint infection, the advent of hybrid imaging with single-photon emission computed tomography(SPECT)/electronic computer X-ray tomography technique (CT) and the availability of fluorine-18 fluoride PET suggests that the diagnostic paradigm may be shifting again. By providing the anatomic information lacking in conventional radionuclide studies, there is renewed interest in bone scintigraphy, performed as a SPECT/CT procedure, for detecting joint instability, mechanical loosening and component malpositioning. Fluoride-PET may provide new insights into periprosthetic bone metabolism. The objective of this manuscript is to provide a comprehensive review of the evolution of nuclear medicine imaging of joint replacements.

The painful total hip replacement: diagnosis and deliverance

Total hip replacement (THR) is a very common procedure undertaken in up to 285 000 Americans each year. Patient satisfaction with THR is very high, with improvements in general health, quality of life, and function while at the same time very cost effective. Although the majority of patients have a high degree of satisfaction with their THR, 27% experience some discomfort, and up to 6% experience severe chronic pain. Although it can be difficult to diagnose the cause of the pain in these patients, this clinical issue should be approached systematically and thoroughly. A detailed history and clinical examination can often provide the correct diagnosis and guide the appropriate selection of investigations, which will then serve to confirm the clinical diagnosis made.

Diagnosis of bone infection by complementary role of technetium-99m MDP and technetium-99m hexamethylpropylene-amineoxime-leukocytes

Purpose:

Valuate complementary role of ^99mTc-MDP bone scan and ^99mTechnetium hexamethylpropylene-amineoxime (^99mTc-HMPAO) labeled leukocyte scintigraphy in diagnosis of bone infection.

Patients and Methods:

Ninety one sites suspected to have bone infection were divided in to two groups: Group I 49 sites with current endo-prothesis; and group II 42 sites with no prosthesis. All patients were subjected to serial images of ^99mTc-HMPAO labeled leukocyte (^99mTc-white blood cells (WBCs)), triple phase bone scan (^99mTc-MDP) and plain X-ray, in addition to clinical and bacteriological assessment, together with follow-up.

Results:

The overall sensitivity (Sn) was found to be 34.9%, 95.4%, and 86% for plain X-ray, ^99mTc-MDP, and ^99mTc-WBCs respectively. Concerning specificity (Sp) was found to be 47.9%, 45.8%, and 91.7% respectively for the three imaging modalities. ^99mTc-WBCs showed better Sn, Sp, and accuracy in group I (95%, 93.1% and 93.9%, respectively) compared to 40%, 41.4%, and 40.8% for plain X-ray and 90%, 62%, and 73.5% respectively for ^99mTc-MDP. On the other hand, ^99mTc-MDP proved to have best Sn 100% versus 78.3% and 30.4% for ^99mTc-WBCs and plain X-ray respectively. Yet, Sp and accuracy was found to best for ^99mTc-WBCs (89.5% and 83.3% respectively) compared to 57.9% and 42.9% for plain X-ray and 21.1% and 64.3% for ^99mTc-MDP.

Conclusion:

Combined imaging with ^99mTc-WBCs and ^99mTc-MDP proved to be effective in early detection of bone infection in the presence or absence of prosthesis.

The Clinical Usefulness of (99m)Tc HMPAO Leukocyte/(99m)Tc Phytate Bone Marrow Scintigraphy for Diagnosis of Prosthetic Knee Infection: A Preliminary Study

PURPOSE

The preferred radionuclide imaging procedure for diagnosing prosthetic joint infection is combined radiolabeled leukocyte/(99m)Tc sulfur colloid bone marrow scintigraphy, which has an accuracy of over 90 %. Unfortunately, sulfur colloid is no longer available in South Korea. In this study, we evaluated the usefulness of (99m)Tc phytate, a substitute for (99m)Tc sulfur colloid, when combined with radiolabeled leukocyte scintigraphy in suspected prosthetic knee infections.

METHODS

Eleven patients (nine women, two men; mean age 72 ± 6 years) with painful knee prostheses and a suspicion of infection underwent both (99m)Tc HMPAO leukocyte scintigraphy (LS) and (99m)Tc phytate bone marrow scintigraphy (BMS). The combined images were interpreted as positive for infection when radioactivity in the LS at the site of clinical interest clearly exceeded that of the BMS (discordant); they were interpreted as negative when the increased activity in the LS was consistent with an increased activity in the BMS (concordant). The final diagnosis was made with microbiological or intraoperative findings and a clinical follow-up of at least 12 months.

RESULTS

Five of eleven patients were diagnosed as having an infected prosthesis. The overall sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy of the combined LS/BMS were 100 %, 83 %, 83 %, 100 % and 91 %, respectively.

CONCLUSION

We find that combined (99m)Tc HMPAO LS/(99m)Tc phytate BMS shows comparable diagnostic performance to other studies utilizing sulfur colloid. Combined (99m)Tc HMPAO LS/(99m)Tc phytate BMS is therefore expected to be an acceptable alternative to combined radiolabeled LS/(99m)Tc sulfur colloid BMS for diagnosing prosthetic knee infections.

Prosthetic joint infections: radionuclide state-of-the-art imaging

Prosthetic joint replacement surgery is performed with increasing frequency. Overall the incidence of prosthetic joint infection (PJI) and subsequently prosthesis revision failure is estimated to be between 1 and 3%. Differentiating infection from aseptic mechanical loosening, which is the most common cause of prosthetic failure, is especially important because of different types of therapeutic management. Despite a thorough patient history, physical examination, multiple diagnostic tests and complex algorithms, differentiating PJI from aseptic loosening remains challenging. Among imaging modalities, radiographs are neither sensitive nor specific and cross-sectional imaging techniques, such as computed tomography and magnetic resonance imaging, are limited by hardware-induced artefacts. Radionuclide imaging reflects functional rather than anatomical changes and is not hampered by the presence of a metallic joint prosthesis. As a result scintigraphy is currently the modality of choice in the investigation of suspected PJI. Unfortunately, there is no true consensus about the gold standard technique since there are several drawbacks and limitations inherent to each modality. Bone scintigraphy (BS) is sensitive for identifying the failed joint replacement, but cannot differentiate between infection and aseptic loosening. Combined bone/gallium scintigraphy (BS/GS) offers modest improvement over BS alone for diagnosing PJI. However, due to a number of drawbacks, BS/GS has generally been superseded by other techniques but it still may have a role in neutropenic patients. Radiolabelled leucocyte scintigraphy remains the gold standard technique for diagnosing neutrophil-mediated processes. It seems to be that combined in vitro labelled leucocyte/bone marrow scintigraphy (LS/BMS), with an accuracy of about 90%, is currently the imaging modality of choice for diagnosing PJI. There are, however, significant limitations using in vitro labelled leucocytes and considerable effort has been devoted to developing alternative radiotracers, such as radiolabelled HIGs, liposomes, antigranulocyte antibodies and fragments, as well as more investigational tracers such as radiolabelled antibiotics, antimicrobial peptides, bacteriophages and thymidine kinase. On the other hand, positron emission tomography (PET) is still growing in the field of PJI imaging with radiotracers such as (18)F-fluorodeoxyglucose (FDG), (18)F-FDG white blood cells and (18)F-fluoride. But unfortunately this superb tomographic technique will only receive full acceptance when specific PET uptake patterns can be successfully developed. The emergence of hybrid modality imaging using integrated single photon emission computed tomography (SPECT) and PET with computed tomography (SPECT/CT and PET/CT) may also have a contributing role for more accurate assessment of joint replacement complications, especially combined with new radiotracers such as (68)Ga and (64)Cu. Finally, in searching for infection-specific tracers, currently there is no such diagnostic agent available.

Guidelines for the labelling of leucocytes with (111)In-oxine. Inflammation/Infection Taskgroup of the European Association of Nuclear Medicine

We describe here a protocol for labelling autologous white blood cells with (111)In-oxine based on previously published consensus papers and guidelines. This protocol includes quality control and safety procedures and is in accordance with current European Union regulations and International Atomic Energy Agency recommendations.

Nuclear medicine and the infected joint replacement

Nearly 700,000 hip and knee arthroplasties are performed annually in the United States. Although the results in most cases are excellent, implants do fail. Complications like heterotopic ossification, fracture, and dislocation are now relatively rare and easily diagnosed. Differentiating aseptic loosening, the most common cause of prosthetic joint failure, from infection, is important because their treatments are very different. Unfortunately, differentiating between these 2 entities can be challenging. Clinical signs of infection often are absent. Increased peripheral blood leukocytes, erythrocyte sedimentation rate, and C-reactive protein levels are neither sensitive nor specific for infection. Joint aspiration with Gram stain and culture is the definitive diagnostic test. Its specificity is in excess of 90%; its sensitivity is variable, however, ranging from 28% to 92%. Plain radiographs are neither sensitive nor specific and cross-sectional imaging modalities, such as computed tomography and magnetic resonance imaging, can be limited by hardware-induced artifacts. Radionuclide imaging is not affected by orthopedic hardware and is the current imaging modality of choice for suspected joint replacement infection. Bone scintigraphy is sensitive for identifying the failed joint replacement, but cannot be used to determine the cause of failure. Neither periprosthetic uptake patterns nor performing the test as a 3-phase study significantly improve accuracy, which is only about 50-70%. Thus, bone scintigraphy typically is used as a screening test or in conjunction with other radionuclide studies. Combined bone gallium imaging, with an accuracy of 65-80%, offers only modest improvement over bone scintigraphy alone. Presently, combined leukocyte/marrow imaging, with approximately 90% accuracy, is the radionuclide imaging procedure of choice for diagnosing prosthetic joint infection. In vivo leukocyte labeling techniques have shown promise for diagnosing musculoskeletal infection; their role in prosthetic joint infection has not been established. (111)In-labeled polyclonal immunoglobulin lacks specificity. (99m)Tc-ciprofloaxicin does not consistently differentiate infection from aseptic inflammation. (18)F-fluorodeoxyglucose positron emission tomography has been extensively investigated; its value in the diagnosis of prosthetic joint infection is debatable.

Evaluation and management of the infected total hip and knee

Infection should be in the differentia for any painful total hip or knee. A thorough history and physical, complete set of radiographs and appropriate labs including C-reactive protein and erythrocyte sedimentation rate are essential in the initial evaluation. Ancillary tests such as aspiration and nuclear imaging may be helpful in unclear cases or when labs are concerning for infection. It is essential that all antibiotics are discontinued several weeks prior to gram stain and culture, if possible, to reduce the number of false negative test results. Classifying infection into acute versus late infection aids in the treatment plan. For acute infections presenting within 2 to 4 weeks of symptom onset, irrigation and debridement with polyethylene liner exchange and retention of components may be possible. When attempting component retention, thorough debridement and rapid treatment of the infection prior to the accumulation of any biofilm is paramount for a successful outcome. Other important prognostic factors to consider include the virulence of the microorganism as well as the immune status of the host. Despite expeditious management, irrigation and debridement of acute total hip and knee infections frequently leads to recurrent infection. Thus, patients should be counseled accordingly. Further management may be needed following an initial attempt at component retention. These options include resection arthroplasty with or without re-implantation, long term antibiotic suppressive therapy, arthrodesis and even above the knee amputation in rare circumstances. For chronic infections, a successful outcome depends on several factors including the baseline health status of the patient, implant removal with a thorough debridement followed by culture specific antibiotic treatment. Furthermore, methods of monitoring for persistent infection include following laboratory values such as the C-reactive protein, erythrocyte sedimentation rate, and cultures from joint aspirations. Whether to perform a direct exchange versus a delayed revision arthroplasty for chronic total hip and knee infections can be debated. Several published series have reported successful outcomes with single stage procedures when patients are carefully selected. However, the majority of chronic infections in the United States are treated with two stage resection, since this method has consistently provided the highest cure rates, with many current studies demonstrating >90% success.

White blood cell scintigraphy for differentiation of infection and aseptic loosening: a retrospective study of 76 painful hip prostheses

BACKGROUND

Diagnosis of an infected arthroplasty is often difficult. Fever, abnormal physical findings, radiographic changes, findings at bone scintigraphy, an elevated erythrocyte sedimentation rate, CRP, and leucocytosis are not specific enough. We evaluated the diagnostic value of white blood cell scintigraphy.

METHODS

We retrospectively reviewed 76 cases (66 patients) admitted for white blood cell scintigraphy with a clinical suspicion of infection in a hip prosthesis during the period 1995-2003. The leukocytes were labeled with (99m)Tc-HMPAO or with (111)In-oxin. Anterior and posterior views were taken of both hip joints at 3 different time points after injection: 1 h, 3 h, and 22 h. Infection was verified by means of bacteriological cultures, histopathological findings, intraoperative frozen sections, and follow-up (up to 3.5 years).

RESULTS

Of 76 scintigraphies, 51 were negative and 25 were positive. There were 81% true positive, 94% true negative, 6% false positive, and 19% false negative outcomes.

INTERPRETATION

White blood cell scintigraphy with additional late imaging is an effective tool for differentiation between loosening and infection in painful hip arthroplasty.

Von der tibiofemoralen Instabilität zur Luxation in der Knieendoprothetik

Tibiofemoral instability is increasingly recognized as a mode of failure in total knee arthroplasty (TKA). Severe instability may lead to dislocation. Wrong surgical technique and wrong choice of constraint of the prostheses are the main causes for instability. Malalignment, malrotation and intraoperatively uncorrected instability especially in flexion may lead to an unstable total knee arthroplasty. Cruciate-retaining designs and mobile platforms can be considered only in the presence of well-balanced ligaments. Cruciate-substituting designs give more stability and many people find them more forgiving. However, correction of varus-valgus instability and severe flexion laxity cannot be provided. Varus-valgus contrained designs cannot compensate for the absence of medial and lateral collateral ligaments. Such cases are most reliably treated with a linked implant (rotating hinge). The exact analysis of the cause of an unstable or dislocated total knee arthroplasty represents the most essential basis of a successful treatment. Exchange of the prostheses represents the most successful procedure. Correction of implantation failures should be performed. A more constrained design should be used if insufficient ligaments are found. Post-traumatic instability or dislocation represents an exception.

Evaluation of 99mTc-UBI 29-41 scintigraphy for specific detection of experimental Staphylococcus aureus prosthetic joint infections

PURPOSE

(99m)Tc-UBI 29-41 (UBI), an antimicrobial peptide, specifically targets bacteria. We tested the ability of UBI to discriminate between infected and uninfected prosthetic joints using a rabbit model previously validated.

METHODS

Left knee arthroplasty was performed on 20 New Zealand rabbits, then 10(7) cfu of S. aureus (n = 12) or sterile saline (n = 8) was injected into the joint. On days 9 and 20 after surgery, planar UBI scintigraphy was performed in six infected and four uninfected rabbits, 1 h and 4 h p.i. (150 MBq), on a gamma camera. Operated-to-normal knee activity ratio (ONKR) was calculated on each scintigram. Then, after sacrifice, tissue samples of both knees were counted in a gamma counter.

RESULTS

One rabbit injected with sterile saline had cutaneous infection at sacrifice and was excluded from analysis. ONKR was higher in infected than in uninfected animals 4 h p.i. 20 days after surgery: 1.75 +/- 0.48 vs 1.13 +/- 0.11, p = 0.04. From 1 h to 4 h p.i., ONKR increased in 9/12 infected and 0/7 uninfected animals. According to UBI uptake intensity and kinetics, scintigraphy was truly positive in all infected cases on day 9 and in four of six infected cases on day 20. It was truly negative in two of three sterile inflamed prosthetic knees on day 9, and in all cases on day 20. Biodistribution studies revealed increased UBI uptake in periprosthetic tissues in all animals 9 days after surgery, and only in infected animals on day 20.

CONCLUSION

In this experimental study, (99m)Tc-UBI 29-41 scintigraphy permitted the early detection of acute prosthetic joint infection, and exclusion of infection in chronic sterile prosthetic joint inflammation.

[Diagnostic strategies in cases of suspected periprosthetic infection of the knee. A review of the literature and current recommendations]

Reliable confirmation of periprosthetic infection after total knee arthroplasty is a diagnostic challenge. The present work reviews published data evaluating the available diagnostic tools. Erythrocyte sedimentation rate and C-reactive protein serum levels are relatively sensitive methods with rather low specificity towards periprosthetic infection and are mainly applied to exclude infection. Studies evaluating scintigraphic methods--especially white cell scans--provide inconsistent data with varying accuracy. Consequently, white cell scans cannot be recommended as standard methods. Immunoscintigraphy with antigranulocyte antibodies and FDG-PET scans demonstrated promising results with particularly high sensitivities, but have to be validated in larger studies. Microbiological evaluation of joint aspirates proved high specificity for periprosthetic infection. However, an average of 20% of infected cases remained undetected. Nevertheless, aspiration is widely recommended for preoperative isolation of the infecting organism. Intraoperative frozen sections demonstrated excellent specificity with good sensitivity. The real accuracy of intraoperative culture and permanent histology cannot be determined due to the missing golden standard; however, a combination of both methods is recommended to define the final diagnosis. Large studies validating both methods and criteria for the final diagnosis of periprosthetic infection are necessary to optimize the diagnostic algorithm.

Imaging of musculoskeletal infections

Imaging procedures are routinely used to evaluate patients suspected of having musculoskeletal infection. Radiographs should be performed whenever musculoskeletal infection is suspected. Even when not diagnostic, radiographs are useful. They provide an anatomic overview of the region of interest, including pre-existing conditions that could influence the selection and interpretation of subsequent procedures. Magnetic resonance imaging (MRI) is sensitive, provides superb anatomic detail, does not use ionizing radiation, and is rapidly completed. This technique is especially valuable for septic arthritis, spinal osteomyelitis, and diabetic foot infections. Among the radionuclide procedures, three-phase bone imaging is readily available, and very accurate in unviolated bone. Labeled leukocyte imaging should be used in cases of 'complicating osteomyelitis' such as prosthetic joint infections. This test is also useful in unsuspected diabetic pedal osteomyelitis and the neuropathic joint. Gallium imaging is a useful adjunct to MIR in spinal infection. 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) will likely play an important role, especially in the evaluation of spinal infection.

Nuclear medicine imaging of bone infections

The inflammation and infection of bone include a wide range of processes that can result in a reduction of function or in the complete inability of patients. Apart from the inflammation, infection is sustained by pyogenic microorganisms and results mostly in massive destruction of bones and joints. The treatment of osteomyelitis requires long and expensive medical therapies and, sometimes, surgical resection for debridement of necrotic bone or to consolidate or substitute the compromised bones and joints. Radiographs and bone cultures are the mainstays for the diagnosis but often are useless in the diagnosis of activity or relapse of infection in the lengthy management of these patients. Imaging with radiopharmaceuticals, computed tomography and magnetic resonance are also used to study secondary and chronic infections and their diffusion to soft or deep tissues. The diagnosis is quite easy in acute osteomyelitis of long bones when the structure of bone is still intact. But most cases of osteomyelitis are subacute or chronic at the onset or become chronic during their evolution because of the frequent resistance to antibiotics. In chronic osteomyelitis the structure of bones is altered by fractures, surgical interventions and as a result of bone reabsorption produced by the infection. Metallic implants and prostheses produce artefacts both in computed tomography and magnetic resonance images, and radionuclide studies should be essential in these cases. Vertebral osteomyelitis is a specific entity that can be correctly diagnosed by computed tomography or magnetic resonance imaging at the onset of symptoms but only with radionuclide imaging is it possible to assess the activity of the disease after surgical stabilization or medical therapy. The lack of comparative studies showing the accuracy of each radiopharmaceutical for the study of bone infection does not allow the best nuclear medicine techniques to be chosen in an evidence-based manner. To this end we performed a meta-analysis of peer reviewed articles published between 1984 and 2004 describing the use of nuclear medicine imaging for the study of the most frequent causes of bone infections, including prosthetic joint, peripheric post-traumatic bone infections, vertebral and sternal infections. Guidelines for the choice of the optimal radiopharmaceuticals to be used in each clinical condition and for different aims is provided.

Combined labeled leukocyte and technetium 99m sulfur colloid bone marrow imaging for diagnosing musculoskeletal infection

The use of labeled leukocyte (white blood cell [WBC]) studies in the diagnosis of osteomyelitis can be problematic. A combined study consisting of WBC imaging and complementary bone marrow imaging performed with technetium 99m (99mTc) sulfur colloid is approximately 90% accurate and is especially useful for diagnosing osteomyelitis in situations involving altered marrow distribution. There are limitations and pitfalls associated with a combined study. If there is no labeled WBC activity in the region of interest, marrow imaging is not useful. The sulfur colloid image becomes photopenic within about 1 week after the onset of infection, so that the study should be interpreted cautiously in the acute setting. Labeled WBC accumulation in lymph nodes can also confound image interpretation, although nodal activity can usually be recognized because it is typically round, discrete, multifocal, linear in distribution, and often bilateral. Furthermore, 99mTc-sulfur colloid that is improperly prepared or is more than about 2 hours old degrades image quality, potentially causing erroneous conclusions. Nevertheless, WBC-marrow imaging is a very accurate technique for diagnosing osteomyelitis. Knowledge of the criteria for image interpretation and of the aforementioned limitations and pitfalls, combined with careful attention to imaging technique, will maximize the value of this study.

[Value of radiographic examination of the knee joint for the orthopedic surgeon]

Extended radiographic examinations offer excellent options for diagnosis and strategy for treatment of the knee joint. The whole-leg radiograph is indispensable in measuring alignment for osteotomy or total knee arthroplasty (TKA). Fluoroscopically assisted varus-valgus stress radiographs provide the possibility for verifying mechanical function of the implanted knee prosthesis. Ultrasound examinations have been widely replaced by magnetic resonance imaging (MRI). MRI is the golden standard to examine intra-articular structures of the knee (meniscus, ligaments, cartilage) and surrounding soft tissue. For evaluating femoral and tibial torsion and determining axial rotation of TKA, computed tomography (CT) is best qualified. Imaging of the patellofemoral joint (patella instability) is difficult; CT scans in combination with true lateral radiographs seem to be helpful.

Postoperative Imaging of the Knee

The knee is a frequently injured joint and, thus, a common focus of operative intervention. As operative techniques and imaging modalities evolve, radiologists must be aware of the expected postoperative appearance after knee surgeries that are performed commonly and also must be comfortable recognizing complications encountered commonly in the immediate and delayed postoperative period. Drawing on the large amount of attention this subject has received of late in the radiologic and orthopedic literature, this article reviews the knee surgeries performed most commonly and the expected normal and most frequently encountered abnormal postoperative imaging findings with an emphasis on MR imaging.

Imaging of knee arthroplasty

Knee replacement surgery, either with unicompartmental or total systems, is common. The purpose of this manuscript is to review the appearance of normal knee arthroplasty and the appearances of complications such as infection, polyethylene wear, aseptic loosening and particle-induced osteolysis, patellofemoral abnormalities, axial instability, and periprosthetic and component fracture. Knowledge of the potential complications and their imaging appearances will help the radiologist in the diagnostic evaluation of the patient with a painful knee arthroplasty.

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.

Immunoscintigraphy of septic loosening of knee endoprosthesis: a retrospective evaluation of the antigranulocyte antibody BW 250/183

Immunoscintigraphy with the use of the antigranulocyte antibody BW 250/183 is a reliable method for detecting infection, especially in septic loosening of hip prostheses, for which purpose quantitative interpretation of the time-activity course is employed. Therefore, we retrospectively studied whether similar results could be achieved in knee prostheses. We verified 28 scintigraphic examinations in 26 patients by histology. Scintigraphy was performed during an early (4-6 h post injection) and a late phase (23-25 h post injection). Infection was diagnosed when activity around the knee prosthesis increased by more than 10% compared with bone marrow. We found a sensitivity and a negative predictive value of 100%, a specificity of 80%, a positive predictive value of 81% and an accuracy of 89%. Specificity and accuracy are lower than in the evaluation of hip prostheses; however, in comparison to other scintigraphic modalities, scintigraphy with the antigranulocyte antibody BW 250/183 is superior in excluding infection and has better specificity and accuracy. Therefore, as in the case of hip prostheses, the described methodology appears to be the scintigraphic modality of choice for knee prostheses.

Prosthetic joint infections: bane of orthopedists, challenge for infectious disease specialists

Prosthetic joint infections (PJIs) occur in approximately 1.5%-2.5% of all primary hip or knee arthroplasties. The mortality rate attributed to PJIs may be as high as 2.5%. Substantial morbidity is associated with a loss of mobility, although this is temporary. The costs associated with a single episode of PJI are approximately $50,000 per episode, exclusive of lost wages. Risk factors that increase the occurrence of PJI include revision arthroplasty, time in the operating room, postoperative surgical site infection, and malignancy. Pain is the most consistent symptom. Staphylococcus species are the most common organisms isolated from PJI sites. Two-stage revision is superior to single-stage revision or to debridement with prosthesis retention. Long-term antibiotic suppression and/or arthrodesis are useful for patients too frail to undergo extensive surgery. Using an optimal approach, recurrent infection occurs in <10% of previously infected joints.