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Approach to imaging modalities in the setting of suspected nonvertebral osteomyelitis

Approach to imaging modalities in the setting of suspected nonvertebral osteomyelitis
Author:
Charles E Spritzer, MD
Section Editor:
Sandra Nelson, MD
Deputy Editor:
Keri K Hall, MD, MS
Literature review current through: Jan 2024.
This topic last updated: Jan 28, 2022.

INTRODUCTION — Radiographic imaging is useful for confirming or excluding the diagnosis of osteomyelitis, delineating the extent of disease, and planning therapy (table 1). Imaging findings must be interpreted in clinical context [1]. Osteomyelitis may occur in any bone; the largest body of data on imaging modalities for evaluation of osteomyelitis comes from the literature on diabetic foot infections.

The benefits and limitations of plain radiographs, magnetic resonance imaging, computed tomography, nuclear modalities, and ultrasonography for the diagnosis of osteomyelitis will be reviewed here. An integrated diagnostic approach to evaluation of adults with suspected osteomyelitis is presented in detail separately. (See "Nonvertebral osteomyelitis in adults: Clinical manifestations and diagnosis", section on 'Clinical approach'.)

Issues related to radiographic imaging in the setting of suspected vertebral osteomyelitis and discitis are discussed separately. (See "Vertebral osteomyelitis and discitis in adults".)

PATHOPHYSIOLOGY OF OSTEOMYELITIS — Osteomyelitis can occur as a result of hematogenous seeding, contiguous spread of infection to bone from adjacent soft tissues and joints, or direct inoculation of infection into the bone as a result of trauma or surgery. The most commonly affected adults are individuals with poorly controlled diabetes, peripheral neuropathy, and vascular insufficiency who develop ulcers and subsequent osteomyelitis in one or more bones of the foot [2,3]. (See "Nonvertebral osteomyelitis in adults: Clinical manifestations and diagnosis", section on 'Classification'.)

In the setting of osteomyelitis, inflammatory exudate in the marrow causes elevated medullary pressure, which compresses vascular channels, leading to ischemia and bone necrosis. If the areas of necrotic bone separate from the remaining viable bone, sequestra are formed. Surviving bone and periosteum ultimately produce a sheath of bone surrounding the area of necrosis, which is referred to as an involucrum. Both the sequestra and involucrum may be apparent radiographically (image 1 and image 2) [2-4].

Acute osteomyelitis refers to infection in the bone prior to development of sequestra, usually measured in days or weeks. In some forms of osteomyelitis, development of sequestra is relatively slow (such as vertebral osteomyelitis), while in others the development of sequestra occurs relatively rapidly (such as osteomyelitis in the setting of prosthetic devices or compound fractures) [1].

Following formation of sequestra, the infection is considered to be chronic osteomyelitis. Other hallmarks of chronic osteomyelitis include involucrum, local bone loss, and sinus tracts (extension of infection through cortical bone) (image 1 and image 2). Occasionally, pus may exist in an opening (cloaca) of involucrum.

SELECTING AN IMAGING MODALITY — The evaluation of suspected osteomyelitis includes radiographic imaging interpreted together with the clinical history, culture data, and laboratory results. The optimal imaging modality depends upon the specific clinical circumstances and should be tailored accordingly. An integrated diagnostic approach for osteomyelitis is outlined in detail separately. (See "Nonvertebral osteomyelitis in adults: Clinical manifestations and diagnosis", section on 'Clinical approach'.)

In general, if osteomyelitis is suspected based on clinical history and physical findings, imaging should begin with conventional radiographs (plain x-rays) of the involved area. A more sophisticated imaging modality should be pursued for patients with normal radiographs or radiographs suggestive of osteomyelitis without definitive characteristic features; such imaging may be used to establish a diagnosis of osteomyelitis and/or to define the extent of disease for surgical planning.

Magnetic resonance imaging (MRI) is the imaging modality with greatest sensitivity for diagnosing osteomyelitis; if MRI is contraindicated, positron emission tomography/computed tomography (PET/CT) should be pursued if available. Alternatives include a labeled leukocyte scan, three-phase bone scan, or CT scan [5-7].

Associated soft tissue abnormalities may be assessed with MRI, CT, PET/CT, or ultrasonography.

IMAGING MODALITIES — The sensitivity of conventional radiographs for detection of acute osteomyelitis is limited, and the specificity of some imaging modalities may be limited by confounding bony pathology. Negative predictive values are high for magnetic resonance imaging (MRI) and radionuclide studies.

Conventional radiography — Conventional radiography (eg, plain x-ray) is a reasonable initial imaging modality for evaluation of suspected osteomyelitis in patients with at least two weeks of clinical symptoms; it is not adequate for detection of early osteomyelitis [8]. Conventional radiographs are useful for identification of noninfectious pathology and for identifying air within soft tissues (image 3). The sensitivity of conventional radiographs range from 22 to 75 percent [9]. One meta-analysis including diabetic foot ulcers reported a pooled sensitivity and specificity of 0.54 and 0.68, respectively [10].

Radiographic findings of osteomyelitis include osteopenia and bone resorption, cortical loss, bony destruction, and periosteal reaction [11-14]. There are usually associated soft tissue findings including swelling, loss of fascial planes, and ulceration; soft tissue gas may be observed.

Radiographs may be unremarkable for the first 10 to 14 days following infection [3]. Bony destructive changes on radiography lag at least two weeks behind clinical infection; approximately 50 to 75 percent of the bone matrix must be destroyed before plain radiographs demonstrate lytic changes [15].

Following trauma, radiographic findings of architectural distortion, osteopenia due to disuse, and normal fracture healing may be difficult to distinguish from osteomyelitis [16]. In addition, conventional radiography may be insufficient to distinguish osteomyelitis from other processes such as Charcot arthropathy and fracture [17]. In the presence of orthopedic hardware, findings of osteomyelitis may include fracture, nonunion, or periprosthetic lucency. In the setting of chronic osteomyelitis, reactive sclerosis, sequestra, and involucrum may be observed [11,12].

Magnetic resonance imaging — MRI has excellent sensitivity for diagnosis of osteomyelitis. After conventional radiographic evaluation, MRI is generally considered the study of choice for further assessment [5,6,18-21]. It is useful for obtaining images delineating the extent of cortical destruction characteristic of osteomyelitis, as well as to evaluate for presence of bone marrow abnormality, soft tissue inflammation (such as in the setting of cellulitis, myositis, and/or ulceration), and ischemia (picture 1) [22,23]. MRI may demonstrate abnormal marrow edema as early as one to five days following onset of infection [10,18,24]. Intravenous contrast does not improve the detection of osteomyelitis on MRI but does improve the distinction between phlegmon, necrotic tissue, and abscess.

MRI has high sensitivity and negative predictive value for diagnosis of osteomyelitis [5,7,25-29]. In a 2020 meta-analysis including 36 studies, MRI had a pooled sensitivity and specificity of 96 and 82 percent, respectively; positron emission tomography/computed tomography (PET/CT) had lower sensitivity (84 percent) but greater specificity (93 percent) [25]. Presence of ischemia may diminish the accuracy of MRI for detection of osteomyelitis [28]. Given the high negative predictive value of MRI, an MRI with no evidence of osteomyelitis is sufficient for exclusion of osteomyelitis if clinical signs or symptoms have been present for at least one week [1].

Both T1-weighted and fat-suppressed T2-weighted (or short tau inversion recovery [STIR]) MRIs should be obtained (image 4); these are usually performed in the same imaging plane, and multiple imaging planes are usually obtained. The implementation of Dixon techniques may improve image quality and the detection of both soft tissue and osseous abnormalities [30,31]. Abnormal osseous signal on all sequences in the region of concern in the correct clinical setting confirms the diagnosis of osteomyelitis. Confluent hypointensity on T1-weighted images, cortical erosion, bony destruction, and soft tissue abnormalities adjacent to the bone increase diagnostic confidence [32,33]. Several small studies suggest that bones with overlying ulcers with abnormal signal on T2-weighted or STIR images but normal signal on T1-weighted images have a high likelihood of progressing to osteomyelitis [34]. Absence of osseous signal abnormality on all sequences excludes infection.

MRI may overestimate the extent and duration of infection, given its high sensitivity. Reactive marrow edema seen on fluid sensitive images may coexist with true marrow infection, leading to an imaging abnormality that is larger than the area of actual infection. However, the T1-weighted images likely underestimate the extent of disease. One small study suggests that in the metatarsals, a resection one cm proximal to the T1 abnormality will result in a negative margin for infection 91 percent of the time [35].

Bone marrow signal abnormality on MRI is a nonspecific finding that can be seen with a variety of other pathologies including contusion, fracture, postsurgical change, arthritis, neoplasm, and Charcot arthropathy [36]. Establishing the correct diagnosis depends on the clinical setting and on additional imaging findings. Moreover, if infection coexists with additional pathology that can cause bone marrow edema, MRI cannot reliably distinguish between marrow changes attributable to infection and those attributable to other pathology. Lastly, bone marrow changes may persist for weeks to months after osteomyelitis begins to respond to therapy.

It may be diagnostically challenging to distinguish a diabetic foot with Charcot arthropathy from concomitant infection on MRI. The presence of sinus tracts, fluid collections with thick rim or diffuse enhancement, and extensive adjacent marrow abnormality are concerning for Charcot with superimposed osteomyelitis [37]. In cases of severe Charcot arthropathy, definitive radiographic exclusion of osteomyelitis may not be possible. Preliminary data suggest that techniques such as diffusion-weighted MRI and dynamic contrast-enhanced MRI (DCE-MRI) may help in the differentiation of Charcot arthropathy from osteomyelitis [38-40].

MRI is the imaging modality of choice for delineating the anatomy of the spinal cord and adjacent osseous and soft tissues. (See "Vertebral osteomyelitis and discitis in adults".)

Gadolinium contrast-enhanced images are not required to diagnose acute osteomyelitis. However, the administration of contrast is useful to enhance visualization of sinus tracts, fistulas, and necrotic tissue and to distinguish between abscess and phlegmon (picture 1) [22,23]. The utility of gadolinium contrast-enhanced images is increased in chronic osteomyelitis as areas of active inflammation will enhance and abscesses are well demarcated [18].

As many patients with osteomyelitis also have diabetes with chronic renal insufficiency, avoidance of gadolinium or selection of an appropriate approach to minimize nephrogenic systemic fibrosis (NSF) are important considerations [41]. Preliminary data suggest that ferumoxytol may provide similar information to gadolinium agents without risk of NSF [42].

The penumbra sign, a thin layer of granulation tissue lining a bone abscess cavity, may be seen in osteomyelitis (image 5). This finding produces a higher signal on T1-weighted magnetic resonance images; in one study, it had a sensitivity and specificity of 73 and 99 percent, respectively [43].

Metallic hardware can give rise to artifact that may degrade MRI image quality and limit diagnostic capability.

Computed tomography — CT is more sensitive than conventional radiography for assessing cortical and trabecular integrity, periosteal reaction, intraosseous gas, soft tissue gas, and the extent of sinus tracts (image 6) [13,16,18,44-47]. It is useful in chronic osteomyelitis and may be the most useful modality to evaluate for the presence of osseous sequestra and involucrum [1,21].

Intravenous contrast is required for detection of soft tissue abnormalities such as sinus tracts. Noncontrast CT allows assessment of gas but does not evaluate soft tissue pathology as well as a contrasted CT.

Metallic hardware can give rise to artifact that may degrade CT image quality and limit diagnostic capability (image 7).

Nuclear modalities — A nuclear study may be useful if metal hardware precludes MRI or CT assessment, or if MRI is contraindicated. There are a number of different modalities, including PET scans, usually combined with CT (PET/CT), single photon emission CT (SPECT-CT), and gamma (scintillation or Anger) cameras. Gamma cameras provide planar images; the other modalities provide cross sectional image sets.

These imaging modalities require radiotracers, which may be used alone (eg, Gallium-67) or “tagged” (combined with) to other molecules or cells which target the areas of infection. Examples of such tracers include: Tc-99m, In-111, and F-18. These tracers may be combined with leukocytes (eg, In-111 white blood cell [WBC]), phosphonates (eg, Tc-99m methylene diphosphonate [MDP]), or a glucose analogue (eg, flourine-18-fluorodeoxyglucose [18F-FDG]) [48]. SPECT-CT and gamma cameras use the same isotopes and the two techniques are often combined in the same examination.

In general, nuclear imaging has high sensitivity for detecting evidence of inflammation and therefore tends to be more reliable for evaluation of acute infection than chronic infection. A major limitation of nuclear studies is that radiographic evidence of bone turnover or inflammation due to noninfectious bone pathology may be confused with osteomyelitis [49-52]. Such conditions include recent trauma or surgery, recently healed osteomyelitis, septic arthritis, degenerative joint disease, bone tumors, and Paget disease [53,54]. False-negative results are possible in areas of relative ischemia (a common comorbidity in osteomyelitis) since radiotracer may not be adequately delivered to the target site. Finally, many nuclear studies are time consuming and/or costly.

18F-FDG PET – The advantages of 18F-FDG PET/CT include good accuracy in identifying both acute and chronic osteomyelitis, distinguishing osteomyelitis from neuropathic osteoarthropathy and adjacent soft tissue infection, relatively quick acquisition times compared with WBC scintigraphy, and relative insensitivity to metallic hardware.

Disadvantages include inability to discriminate tumor and inflammation from infection, high cost, false positives due to postsurgical inflammatory changes, relatively limited availability, and radiation exposure [55-57]. Tissue inflammation associated with spinal hardware and spinal degenerative changes are potential confounders [58]. As such, 18F-FDG PET/CT may be useful as an alternative to MRI for circumstances in which MRI is contraindicated or as a supplement when MRI is equivocal.

18F-FDG PET uses 18F-FDG, a glucose analog that accumulates in leukocytes, which in turn accumulate at the site of infection. The 18F-FDG molecule accumulates rapidly even in poorly perfused areas due to its small size [58]. As such, imaging is performed 30 to 60 minutes after tracer injection, making the study faster than other nuclear medicine studies [18]. The tracer provides high-resolution tomographic images and, when combined with CT (18F-FDG PET/CT), provides the anatomic detail of conventional CT scans by superimposing the two image sets. The vast majority of PET studies performed are now actually PET/CT studies.

18F-FDG PET is useful for assessing acute and chronic osteomyelitis [5,7,27,56-61]. A meta-analysis including 36 studies reported sensitivity and specificity of 84 and 93 percent, respectively [25]. Due to the inherent high spatial resolution of 18F-FDG PET/CT, this modality is capable of distinguishing osteomyelitis from adjacent soft tissue infection [56,57].

18F-FDG PET may be useful in distinguishing Charcot arthropathy from normal joints and patients with osteomyelitis [62]. A more recent prospective study involving 31 patients concluded that 18F-FDG PET/CT was more accurate than diffusion weighted MRI and DCE-MRI in distinguishing diabetic foot osteomyelitis from Charcot neuropathy [38].

18F-FDG PET has also been shown to be useful in assessing post-traumatic osteomyelitis [63]. A retrospective study of 135 patients suggested a maximum accuracy of 86 percent for diagnosing fracture related infections with a negative predictive value of 0.91 [64].

18F-FDG PET/CT may be useful for diagnosing spondylodiscitis. (See "Vertebral osteomyelitis and discitis in adults".)

Three-phase bone scan – Three-phase bone scans use a radionuclide tracer (typically technetium-99m bound to a phosphorus-containing compound (eg, Tc-99m MDP) that accumulates in areas of bone turnover and increased osteoblast activity [53]. The scans are performed using a gamma camera at three points following tracer injection: immediately after injection (blood flow phase), 15 minutes after injection (blood pool phase), and four hours after injection (osseous phase). In the setting of osteomyelitis, there is intense uptake in all three phases; in the setting of cellulitis, there is increased activity only in the first two phases and normal or mild diffuse increased activity in the third phase [13].

The sensitivity and specificity of three-phase bone scan for detection of osteomyelitis varies depending on the appearance of correlative radiographs. If conventional radiographs are normal, three-phase bone scan has a sensitivity and specificity of about 95 percent [1,53,65]. If radiographs demonstrate noninfectious disorders such as fracture, orthopedic hardware, heterotrophic ossification, arthritis, or Charcot arthropathy, (entities associated with bone formation and radionuclide tracer uptake), sensitivity remains high, but specificity significantly declines resulting in many false-positive results. Adjacent soft tissue infection also decreases specificity [57,66]. Finally, neoplasms can accumulate radiotracer [48]. False-negative results are possible in early osteomyelitis or in the setting of chronic osteomyelitis with impaired blood flow or infarction [54]. In one meta-analysis, the pooled sensitivity and specificity of three-phase bone scans for detecting acute osteomyelitis were 0.81 and 0.28, respectively [10].

Tagged WBC scan – A tagged WBC, also known as a tagged leukocyte scan, uses autologous WBCs and requires a circulating WBC concentration of at least 2000 per microliter [20]. The WBCs are labeled with indium 111 oxyquinoline, gallium-67, or technetium-99m [1]. To perform the study, blood is drawn from the patient, and the white blood cells are separated for labeling with tracer; after a few hours, the tagged white cells are returned to the patient's circulation via intravenous injection. The time of imaging is dependent upon the isotope used. For technetium-99m, imaging begins four to six hours after administration and may be repeated at 18 and 30 hours. For indium-111, images are acquired 18 to 30 hours following injection [18]. The tagged white cells accumulate in the bone marrow and at sites of inflammation or infection; they are not specific for bone. The different tagging agents result in different advantages and disadvantages for the agent used. For example, indium 111-labeled WBCs are more stable than those tagged with technetium 99m, but the scans are of much lower resolution [58].

Tagged WBC scans have similar sensitivity to bone scans for evaluation of osteomyelitis [67]. Reported sensitivities and specificities range from 72 to 100 percent and 67 to 100 percent, respectively [58]. In a meta-analysis comprising 206 patients undergoing indium-111 WBC scintigraphy, a 92 percent sensitivity and 75 percent specificity were reported. In the same meta-analysis, using technetium-99m hexamethylpropyleneamine oxime (HMPAO) in 406 patients, the specificity improved to 92 percent with a sensitivity of 91 percent [7].

Studies suggest that technetium-99m HMPAO is useful in patients with Charcot arthropathy when combined with bone scintigraphy; however, tagged WBC scans can be falsely positive in the setting of other causes of inflammation including fracture [68]. However, a retrospective study of 162 patients undergoing technetium-99m HMPAO WBC scintigraphy for possible fracture related infection in the extremities reported 0.79 percent sensitivity, 0.97 percent specificity, with 0.93 percent negative predictive value and 0.91 percent positive predictive value [69].

Despite these findings, specificity can be poor if corresponding radiographs are not normal [67]. False-negative results are possible in the setting of chronic osteomyelitis when white cell migration to sites of infection is decreased. In addition, regions with substantial quantities of red marrow (such as the vertebral bodies) are not visualized reliably with this modality; WBC scans may best be used in the distal extremities [54].

Finally, WBC scintigraphy necessitates a time consuming and somewhat complex preparation and has the added disadvantage of being expensive [57].

Gallium and dual tracer scans – Gallium scans utilize the affinity of gallium-67 to acute phase reactants (lactoferrin, transferrin, and others) to demonstrate areas of inflammation that may be related to infection [67].

This method is quite sensitive and more specific than three-phase bone scan (sensitivity and specificity 25 to 80 and 67 percent, respectively) [70,71]. If negative, gallium scans effectively exclude the diagnosis of osteomyelitis [1]. False-positive results can occur in the setting of uptake related to fracture and neoplasm; correlative radiographs may help to evaluate for these entities. At present, gallium imaging is limited primarily to the spine [58].

Scanning is typically performed 18 to 72 hours following gallium injection and therefore should be reserved for patients who are clinically stable and do not require prompt imaging results for urgent management decisions [18].

A gallium scan can be performed concurrently with a technetium-labeled three-phase bone scan, and the information gathered may be more useful than that obtained from either examination alone [71]. In this instance, both radionuclide species are injected at the same time. Then, bone scan images can be obtained three to four hours after injection, and gallium scan images can be obtained up to 24 hours later. The result is considered positive when gallium tracer uptake is greater than that of the bone scan.

This older modality is used less commonly than the other nuclear modalities described above [58]. Besides its relative lack of specificity, gallium-67 studies require one to three days for completion; in addition, compared with other isotopes, result in a relatively high radiation dose [48].

SPECT-CT – Single photon emission CT (SPECT-CT) has been shown to increase the accuracy of gallium studies, tagged WBC studies, and three-phase bone scans. Improved localization of the site of osteomyelitis and, more importantly, improved distinction between soft tissue infection and osteomyelitis have been reported [72]. The use of SPECT-CT has also shown to improve the accuracy of tagged WBC studies in post-traumatic osteomyelitis [63]. CT has been shown to increase the accuracy of gallium studies, tagged WBC studies, and three-phase bone scans. This tool allows improved distinction between soft tissue infection and osteomyelitis as well as improved localization of osteomyelitis [72]. New iterative techniques hold promise of increased infection localization with reduced acquisition times [73].

Newer radiotracers – Attempting to overcome limitations listed above, multiple radiotracers for both PET/CT and more conventional radionuclide imaging are in development and are being assessed in animal models [48].

Ultrasonography — Ultrasound may be a useful diagnostic tool for circumstances in which other modalities are not readily available. Typically, bone is not well depicted by ultrasound, because the cortical surface of the bone reflects the acoustic energy that is used to generate ultrasound images. However, changes superficial to cortical bone can be visualized by ultrasound.

In osteomyelitis, ultrasound can demonstrate elevation and/or thickening of the periosteum due to pus emanating from the bone [74-76]. Ultrasound may be more useful for detection of these findings in pediatric patients, since the periosteum in the pediatric skeleton is more loosely adherent to the cortex than in the adult skeleton [1,18]. Ultrasonography is considered excellent for aspirating suspected infected fluid collections or abscesses [77]. (See "Overview of the clinical manifestations of sickle cell disease" and "Hematogenous osteomyelitis in children: Evaluation and diagnosis", section on 'Ultrasonography'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Osteomyelitis and prosthetic joint infection in adults".)

SUMMARY

If osteomyelitis is suspected based on clinical history and physical findings, imaging should begin with conventional radiographs of the involved area for patients with at least two weeks of clinical symptoms. A more sophisticated imaging modality should be pursued for patients with less than two weeks of symptoms, normal radiographs, or radiographs suggestive of osteomyelitis without definitive characteristic features. (See 'Selecting an imaging modality' above.)

Magnetic resonance imaging (MRI) is the imaging modality with greatest sensitivity for diagnosis of osteomyelitis; if MRI is not feasible, appropriate alternative tests include fluorine-18-fluorodeoxyglucose positron emission tomography (18F-FDG PET) computed tomography (CT), tagged white blood cell (WBC) or three-phase bone scan, or single photon emission CT (SPECT-CT). Standard CT may be useful for chronic osteomyelitis. (See 'Selecting an imaging modality' above and "Nonvertebral osteomyelitis in adults: Clinical manifestations and diagnosis", section on 'Clinical approach'.)

In the setting of osteomyelitis, inflammatory exudate in the marrow causes elevated medullary pressure, which compresses vascular channels, leading to ischemia and bone necrosis. If the areas of necrotic bone separate from the remaining viable bone, sequestra are formed. Surviving bone and periosteum ultimately produce a sheath of bone surrounding the area of necrosis, which is referred to as an involucrum. Both the sequestra and involucrum may be apparent radiographically. (See 'Pathophysiology of osteomyelitis' above.)

Findings of osteomyelitis on conventional radiography include osteopenia, cortical loss, bony destruction, and periosteal reaction. Other chronic findings include reactive sclerosis, sequestra, and involucrum. There are usually soft tissue changes, including swelling, ulceration, and possibly air within the soft tissues. Conventional radiographs are also useful for identification of noninfectious pathology. However, conventional radiography may be insufficient to distinguish osteomyelitis from other processes such as Charcot arthropathy and fracture. (See 'Conventional radiography' above.)

MRI has high sensitivity and negative predictive value for diagnosis of osteomyelitis. MRI may demonstrate abnormal marrow edema as early as one to five days following onset of infection, and an MRI with no evidence of osteomyelitis is sufficient for exclusion of osteomyelitis in patients with symptoms for at least one week. MRI is useful for delineating the extent of cortical destruction characteristic of osteomyelitis, as well as for detecting presence of bone marrow and soft tissue inflammation (such as in the setting of cellulitis, myositis, and/or ulceration). However, MRI may overestimate the extent and duration of infection and cannot reliably distinguish between marrow changes attributable to infection and those attributable to other pathology. Intravenous gadolinium contrast does not improve the detection of acute osteomyelitis but does improve the distinction between phlegmon, necrotic tissue, and abscess. (See 'Magnetic resonance imaging' above.)

CT is more sensitive than conventional radiography for assessing cortical and trabecular integrity, periosteal reaction, intraosseous gas, soft tissue gas, and the extent of sinus tracts. It is the most useful modality to evaluate for the presence of osseous sequestra and involucrum. (See 'Computed tomography' above.)

If metal hardware precludes MRI or CT, or if MRI is contraindicated, a nuclear study may be useful. While 18F-FDG PET/CT may provide similar diagnostic accuracy as MRI, its high cost preclude routine use. Tagged WBC studies combined with three-phase bone scan (plus or minus SPECT-CT) may be more practical choices. SPECT-CT improves the accuracy of tracer imaging alone. Tagged WBC and three-phase bone scans have high sensitivity for detecting evidence of inflammation and therefore tend to be more reliable for evaluation of acute infection than chronic infection. However, a major limitation is that radiographic evidence of bone turnover or inflammation due to noninfectious bone pathology may be confused with osteomyelitis. (See 'Nuclear modalities' above.)

Ultrasound may be a useful diagnostic tool in circumstances where the more preferred modalities are not readily available. This may be especially true in the pediatric population. In addition, ultrasound is excellent for aspirating suspected infected fluid collections or abscesses. (See 'Ultrasonography' above.)

ACKNOWLEDGMENT — The editorial staff at UpToDate acknowledge Dr. Perry Horwich and Dr. Mary Hochman, who contributed to earlier versions of this topic review.

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Topic 7653 Version 27.0

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