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Department of Radiology, Nuclear Medicine and Molecular Imaging, University Medical Center Groningen, University of Groningen, Hanzeplein 1, PO Box 30.001, Groningen 9700 RB, the Netherlands
The diagnostic performance of fludeoxyglucose F 18 (18F-FDG) positron emission tomography (PET) in detecting periprosthetic joint infection (PJI) in hip and knee replacements seems sufficiently high for routine clinical application and adds to conventional tests in terms of diagnostic accuracy.
•
Iterative metal artifact reduction of computed tomography data improves PET image quality around prostheses.
•
Location rather than intensity of 18F-FDG uptake is critical in diagnosing hip and knee PJI.
•
18F-FDG uptake at the middle portion of the femoral shaft at the bone-prosthesis interface is highly suspicious for hip PJI.
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18F-FDG uptake at the bone-prosthesis interface has been consistently reported as diagnostic criterion for knee PJI.
Introduction
In 2010, a little more than 2% of the US population were living with a hip or total knee replacement, which corresponds to approximately 7 million people.
and increasing life expectancy of the general population, the prevalence of hip and knee replacements will continue to increase. Hip and knee replacements can improve function and quality of life of individuals with severe arthritis.
A major disadvantage, however, is that approximately 6% of all hip and knee replacements need to be revised after 5 years, which rises to as many as 12% after 10 years.
More than 25% of revisions are attributed to periprosthetic joint infection (PJI), which is a severe complication and associated with substantial morbidity
Other causes for revisions are polyethylene wear and aseptic loosening, fractures, and dislocations. Whereas fractures and dislocations can readily be distinguished by radiography or computed tomography (CT), it may be difficult to differentiate PJI from aseptic loosening. Accurate preoperative diagnosis of PJI is highly desirable, however, because it determines the method of treatment. Aseptic loosening is treated in a 1-stage revision procedure (prosthesis removal and direct implantation of a new prosthesis), whereas a 2-stage revision procedure (prosthesis removal and delayed reimplantation of a new prosthesis)
A majority of PJIs occurring within 1 year of surgery are caused by introduction of bacteria at the time of prosthesis placement, which can occur either through direct contact or aerosolized contamination.
Contiguous spread from an adjacent site is the second mechanism by which PJI can be initiated. This can occur either in the early postoperative period (spread of superficial surgical site infection through incompletely healed superficial and deep fascial planes) or also many years postoperatively (if the normal tissue plane is disrupted again by trauma or surgery).
Table 1Proposed scoring-based definition for periprosthetic joint infection
Adapted from Parvizi J, Tan TL, Goswami K, et al. The 2018 Definition of Periprosthetic Hip and Knee Infection: An Evidence-Based and Validated Criteria. J Arthroplasty. 2018 May;33(5):1309-1314.e2. https://doi.org/10.1016/j.arth.2018.02.078. Epub 2018 Feb 26; with permission.
Major Criteria (at Least One)
Decision
Two positive cultures of the same organism
Infected
Sinus tract with evidence of communication to the joint or visualization of the prosthesis
Minor Criteria, Preoperative
Score
Decision
Serum
Elevated CRP or D-dimer
2
≥6 infected 2–5 possibly infected 0–1 not infected
Elevated ESR
1
Synovial
Elevated white blood cell count or leukocyte esterase
The typical clinical presentation of PJI is a patient with a painful, warm, stiff, and swollen joint. Clinical presentation, however, frequently is atypical, especially in chronic and low-grade infections, and there are no clinical signs that achieve both high sensitivity and high specificity in diagnosing PJI. A painful joint is the most sensitive but least specific clinical finding in PJI.
Signs of deep tissue involvement (ie, sinus tract, purulence, abscess, and extensive necrosis) are the most specific signs and, when present, justify the condition of major criteria for the diagnosis of PJI.
Clinical findings differ based on the type of joint involved (hip or knee) as well as on the timing and presentation of PJI (ie, early postoperative, acute hematogenous, and chronic).
Preoperative synovial fluid culture and serum and synovial fluid analysis for infection markers may be helpful to rule in or rule out PJI (see Table 1). An important limitation, however, is the considerable percentage of dry taps, that is, cases in which no fluid can be aspirated despite appropriate anatomic location within the prosthetic hip or knee joint capsule. This percentage has been reported to be as high as 23% and it does not imply that PJI is not present.
and false-positive cultures when synovial fluid samples are contaminated. Even when using the updated evidence-based and validated major and minor criteria for PJI,
Moreover, there are conditions (adverse local tissue reaction, crystalline deposition arthropathy, inflammatory arthropathy flare, and infection with slowly growing organisms [such as Propionibacterium acnes and coagulase-negative Staphylococci]) in which the criteria may be inaccurate.
and magnetic resonance imaging (MRI) using metal artifact reduction sequences may be more accurate, because they can detect soft tissue abnormalities associated with PJI, included among which are periarticular fluid collections, joint effusion, synovitis, lymphadenopathy, and sinus tracts.
The accuracy of these cross-sectional imaging modalities, however, has not yet been widely validated. Granulomatous reactions to wear, the concurrence of adverse local tissue reaction and PJI, and underlying rheumatoid diseases may impede assessment by CT and MRI.
There are several nuclear imaging techniques that can be used to evaluate suspected PJI. Bone scintigraphy with technetium Tc 99m (99mTc)-labeled diphosphonates or, alternatively, sodium fluoride F 18 PET
; positive findings can indicate either PJI or aseptic loosening. Moreover, a bone scan may be positive for at least 2 years after hip replacement and at least 5 years after knee replacement due to physiologic bone remodeling.
Because bone scintigraphy with 99mTc-labeled diphosphonates is relatively cheap, it may be used as an initial screening test for suspected PJI. Labeled leukocyte imaging has shown superior accuracy for diagnosing PJI compared with bone scintigraphy.
Furthermore, hematopoietically active marrow usually develops around joint prostheses, producing an alteration of the normal bone marrow distribution. This problem may be overcome by late imaging (after 20–24 hours). In PJI, further accumulation of labeled leukocytes is seen in the late images due to increased uptake in infected areas and reduction in background activity.
Clinical indications, image acquisition and data interpretation for white blood cells and anti-granulocyte monoclonal antibody scintigraphy: an EANM procedural guideline.
Labeled leukocyte scintigraphy has other important drawbacks, including its complexity, high costs, potential hazards due to the direct handling of blood products, and considerable radiation burden.
Fludeoxyglucose F 18 (18F-FDG) PET is practically superior, because it is routinely available, provides a completed examination within 1 hour after 18F-FDG administration (rather than 24 hours for labeled leukocyte imaging), and has a favorable safety profile (lack of pathogens in the final product).
In inflammatory conditions, the affinity of glucose transporters for 18F-FDG is increased by various cytokines and growth factors. 18F-FDG is transported into cells by glucose transporters and is phosphorylated by hexokinase enzyme to 18F-FDG-6 phosphate but is not metabolized. The degree of 18F-FDG uptake is related to the metabolic rate and the number of glucose transporters in leukocytes.
FDG PET for diagnosing infection in hip and knee prostheses: prospective study in 221 prostheses and subgroup comparison with combined (111)In-labeled leukocyte/(99m)Tc-sulfur colloid bone marrow imaging in 88 prostheses.
In contrast to labeled leukocyte imaging, 18F-FDG uptake does not rely on leukocyte migration. Therefore, treatment with antibiotics is less likely to affect its sensitivity in delineating the PJI site.
FDG PET for diagnosing infection in hip and knee prostheses: prospective study in 221 prostheses and subgroup comparison with combined (111)In-labeled leukocyte/(99m)Tc-sulfur colloid bone marrow imaging in 88 prostheses.
Fludeoxyglucose F 18 positron emission tomography protocol
Recommendations with regard to patient preparation and precautions, 18F-FDG dose, and image acquisition have been outlined in detail in the European Association of Nuclear Medicine/Society of Nuclear Medicine and Molecular Imaging guideline for 18F-FDG use in inflammation and infection.
Improving CT-based PET attenuation correction in the vicinity of metal implants by an iterative metal artifact reduction algorithm of CT data and its comparison to dual-energy-based strategies: a phantom study.
Improving CT-based PET attenuation correction in the vicinity of metal implants by an iterative metal artifact reduction algorithm of CT data and its comparison to dual-energy-based strategies: a phantom study.
Improving CT-based PET attenuation correction in the vicinity of metal implants by an iterative metal artifact reduction algorithm of CT data and its comparison to dual-energy-based strategies: a phantom study.
Diagnostic performance of fludeoxyglucose F 18 positron emission tomography
The diagnostic performance of 18F-FDG PET in detecting PJI in hip and knee replacements seems sufficiently high for routine clinical application and has not proved inferior to labeled leukocyte scintigraphy.
FDG PET for diagnosing infection in hip and knee prostheses: prospective study in 221 prostheses and subgroup comparison with combined (111)In-labeled leukocyte/(99m)Tc-sulfur colloid bone marrow imaging in 88 prostheses.
Another meta-analysis reported a pooled sensitivity of 70% (95% CI, 56% to 81%) and a pooled specificity of 84% (95% CI, 76% to 90%) for knee prostheses.
In addition, 18F-FDG PET has shown useful in patients with nonspecific clinical presentation (ie, without apparent clinical signs and symptoms, such as absence of a sinus tract).
Furthermore, it has additional value to conventional tests (including radiography, erythrocyte sedimentation rate [ESR]/C-reactive protein [CRP] testing, and joint aspiration culture and white blood cell count) in diagnosing PJI (ie, it increases accuracy).
Differentiating between PJI and inflammation secondary due to foreign body reaction and/or aseptic loosening can be difficult. In noninfected hip prostheses, 18F-FDG uptake is commonly seen around the neck
In noninfected hip prostheses, there should be no 18F-FDG uptake in the periprosthetic soft tissues, except for the soft tissue near the greater trochanter.
18F-FDG PET can identify soft tissue abscesses, which are not apparent on clinical examination (Fig. 3) and, when present, it justifies the condition of major criteria for the diagnosis of PJI.
18F-FDG uptake at the middle portion of the femoral shaft is virtually never seen in asymptomatic patients or in those with aseptic loosening and is highly suspicious for PJI (Fig. 4).
Most studies that have been performed to date have evaluated visual 18F-FDG uptake patterns associated with aseptic loosening or PJI. There is no accepted standardized uptake value (SUV) threshold to diagnose PJI. More importantly, the intensity of 18F-FDG uptake is less important than the location of increased 18F-FDG uptake to diagnose PJI.
The pattern of 18F-FDG uptake around noninfected knee prostheses has been less well documented than that of hip prostheses. Nonspecific synovial 18F-FDG uptake in knee prostheses has been reported by several studies
Diagnosing infection in the failed joint replacement: a comparison of coincidence detection 18F-FDG and 111In-labeled leukocyte/99mTc-sulfur colloid marrow imaging.
The implications of 18F-FDG PET for the diagnosis of endoprosthetic loosening and infection in hip and knee arthroplasty: results from a prospective, blinded study.
(Fig. 5). On the other hand, 18F-FDG uptake at the bone-prosthesis interface of the femoral or tibial component has been consistently reported as diagnostic criterion for PJI in knee prostheses
(Fig. 6). The influence of 18F-FDG uptake, however, at specific bone-prosthesis locations on diagnostic performance has not been reported yet, to the authors’ knowledge. Table 3 summarizes areas of nonspecific 18F-FDG uptake and criteria for PJI in hip and knee prostheses, based on available evidence.
Fig. 1Nonspecific 18F-FDG uptake in a 66-year-old woman with bilateral asymptomatic total hip prostheses. This patient underwent 18F-FDG PET to evaluate a lung lesion. Coronal PET image (B) shows nonspecific 18F-FDG uptake around the neck of the left hip prosthesis (arrowheads), with corresponding CT image (A).
Fig. 2Nonspecific 18F-FDG uptake in a 70-year-old man with asymptomatic right total hip prosthesis. This patient underwent 18F-FDG PET to identify the cause of fever of unknown origin. Coronal PET image (B) shows nonspecific 18F-FDG uptake around the neck (arrowheads) and nonspecific 18F-FDG uptake at lateral side of the acetabular cup (arrow), with corresponding CT image (A).
Fig. 3PJI in an 80-year-old woman with painful left hip prosthesis. Axial (A, B) and coronal (C, D) CT and PET images are displayed. There is a fluid collection in the left iliacus (arrows [A, C]) muscle, which shows peripheral 18F-FDG uptake and no central 18F-FDG uptake (arrows [B, D]), compatible with an abscess. This abscess was not suspected clinically and extended caudally to the left hip joint. In addition, there is 18F-FDG uptake at the bone-prosthesis interface around the acetabular cup and at the proximal femoral stem (arrowheads [D]).
Fig. 4PJI in a patient with bilateral prosthesis. Coronal PET image reveals 18F-FDG uptake at the middle portion of the femoral shaft at the bone-prosthesis interface (arrow), which is highly suspicious for PJI. PJI was confirmed by further assessment.
(From Saboury B, Ziai P, Parsons M, et al. Promising Roles of PET in Management of Arthroplasty-Associated Infection. PET Clin 2012; 7:139-50; with permission.)
Fig. 5Nonspecific synovial 18F-FDG uptake in an asymptomatic knee prosthesis of a 70-year-old man, as shown on coronal (A) and sagittal (B) PET images (arrowheads), with corresponding CT images (C, D).
Fig. 6PJI in a patient with a left knee prosthesis. Coronal PET image demonstrates a focus of intense 18F-FDG uptake in the medial aspect of femoral component at the bone-prosthesis interface (arrow). Operative findings and histopathology confirmed the presence of infection.
(From Saboury B, Ziai P, Parsons M, et al. Promising Roles of PET in Management of Arthroplasty-Associated Infection. PET Clin 2012; 7:139-50; with permission.)
Table 3Areas of nonspecific fludeoxyglucose F 18 uptake and criteria for periprosthetic joint infection in hip and knee prostheses, based on available evidence
Areas of Nonspecific Fludeoxyglucose F 18 Uptake
Criteria for Periprosthetic Joint Infection
Hip
•
Around the neck of the prosthesis
•
Lateral and medial sides of the acetabular cup
•
Proximal portion of the femoral component
•
Distal portion of the femoral component
•
18F-FDG uptake at the middle portion of the femoral component
The occurrence rate of PJI after total shoulder replacement is approximately 1% to 3.9% and can be even higher in reversed designs due to an increase in dead space and hematoma formation.
it can be anticipated that the number of patients with PJI also will increase. The value of 18F-FDG PET in evaluating shoulder PJI, however, has not yet been extensively investigated. The results of a recent study suggested that 18F-FDG PET has poor diagnostic accuracy in diagnosing low-grade PJI of the shoulder.
ROSA Study Group Labeled white blood cell/bone marrow single-photon emission computed tomography with computed tomography fails in diagnosing chronic periprosthetic shoulder joint infection.
In addition, the performance and place of 18F-FDG PET in the diagnostic decision tree of suspected PJI in other less common arthroplasty sites, such as the elbow and ankle, also remains to be investigated. The potential of 18F-FDG PET in evaluating elbow prosthesis already has been demonstrated,
but diagnostic accuracy data are not available yet.
Future perspectives
Although diagnostic performance of 18F-FDG PET in detecting hip and knee PJI seems sufficiently high for clinical use, results from several individual studies were heterogeneous.
Importantly, the definition of PJI has evolved over the years with the most recent updated evidence-based and validated definition for PJI published in 2018.
Most 18F-FDG PET studies performed so far, however, used various other/older definitions of PJI, which may have been an important source of heterogeneity. Standardization of 18F-FDG PET acquisition protocols, diagnostic criteria, and reference standard is required to further explore potential causes of heterogeneity (including type and age of prosthesis) and to further validate this method, preferably by multicenter studies. Large prospective studies comparing the diagnostic performance of 18F-FDG PET and labeled leukocyte imaging for PJI are anticipated.
Simultaneous PET and MRI (integrated PET/MRI) has high potential to improve the noninvasive diagnosis of PJI in 1 single examination, because it combines the functional information gathered from PET and the excellent anatomic detail and soft tissue contrast from MRI.
Diagnosing PJI can be a challenge, especially for chronic and low-grade infections. The diagnostic performance of 18F-FDG PET in detecting PJI in hip and knee replacements seems sufficiently high for routine clinical application and adds to conventional tests. Location rather than intensity of 18F-FDG uptake is critical in diagnosing hip and knee PJI. 18F-FDG uptake at the middle portion of the femoral component and 18F-FDG uptake at the bone-prosthesis interface can be considered positive criteria for PJI in hip and knee prostheses, respectively. The role of 18F-FDG PET in other prosthetic joints remains to be investigated.
Disclosure
All authors have no disclosures to declare.
References
Maradit Kremers H.
Larson D.R.
Crowson C.S.
et al.
Prevalence of total hip and knee replacement in the United States.
Clinical indications, image acquisition and data interpretation for white blood cells and anti-granulocyte monoclonal antibody scintigraphy: an EANM procedural guideline.
FDG PET for diagnosing infection in hip and knee prostheses: prospective study in 221 prostheses and subgroup comparison with combined (111)In-labeled leukocyte/(99m)Tc-sulfur colloid bone marrow imaging in 88 prostheses.
Improving CT-based PET attenuation correction in the vicinity of metal implants by an iterative metal artifact reduction algorithm of CT data and its comparison to dual-energy-based strategies: a phantom study.
Diagnosing infection in the failed joint replacement: a comparison of coincidence detection 18F-FDG and 111In-labeled leukocyte/99mTc-sulfur colloid marrow imaging.
The implications of 18F-FDG PET for the diagnosis of endoprosthetic loosening and infection in hip and knee arthroplasty: results from a prospective, blinded study.