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· Discitis – lateral spine radiographs show late changes at 2–3 weeks into illness, especially decreased intervertebral space and/or erosion of the vertebral plate. · Vertebral OM – initially shows localised rarefication (‘thinning’) of a single vertebral body, then anterior bone destruction. Magnetic resonance imaging (MRI) may be indicated in suspected spondylodiscitis and vertebral or pelvic OM. Magnetic resonance imaging is the most informative imaging modality for OM because it can detect abnormalities within 3-5 days of disease onset. Moreover, it reveals details of the bone and soft tissue involvement, including the formation of abscesses and sequestra, and can help the orthopaedic surgeon to plan the most appropriate surgery for diagnostic and/or therapeutic purposes. MRI may not be necessary in certain situations where other clinical and diagnostic tools are strongly suggestive of the diagnosis. In general, clinicians may wait for 2-3 days to determine the antibiotic response before an imaging study, additional to plain Xray is performed in acute OM, unless the child is very sick, there are reasonable doubts about the diagnosis, or when a complication is suspected. · OM – high sensitivity and specificity (71), it may also demonstrate subperiosteal abscesses, pyomyositis, evidence of contiguous venous thrombosis; more sensitive than bone scan for S. aureus OM (72). · SA – may reveal valuable additional information, such as bone oedema (or even involvement, i.e. associated OM) and perifocal myositis – MRI is not generally indicated for SA. However, it may be valuable if OM-SA is suspected. Thus, in a recent study (18), 35% of children with acute OM had a contiguous SA. © ESPID 2017 – Practice Guideline – Bone and Joint Infections page 15 · Spondylodiscitis and vertebral OM – for detailing bone and soft tissue involvement, discriminate between vertebral OM, epidural abscess and tumour; MRI is a necessary test if these infections are suspected. · Pyomyositis – high sensitivity and specificity, especially useful for the hip and pelvis. · Availability and access – although not (immediately/timely) available in each and every medical centre, most European centres will have access to an MRI. · Disadvantages of MRI include long scan times, susceptibility to motion artefacts which necessitate sedation or anaesthesia in young children, and is a contraindication in some patients with metallic foreign bodies and certain types of implanted hardware (11). · Whole body MRI may be considered as an alternative to bone scan in settings where it is possible and affordable (11,73). Computerized tomography (CT scan) is not generally recommended; it is less sensitive compared to MRI in detecting early osseous lesions and exposes children to high radiation doses (19). It may be performed in settings where MRI is not feasible. · Chronic OM – effectively demonstrates air, sequestra, cortical destruction (74) · Discitis – non-specific results · Valuable for guided procedures, such as aspiration or drainage (18,75) · The advantages over MRI may be its widespread availability and less need for general anaesthesia in young children due to the short time needed for the procedure. Sonography or ultrasound (US) is most indicated for SA since it has a high sensitivity for the diagnosis of joint effusion, although with a lower specificity. In many cases it cannot discriminate between SA and other inflammatory conditions. It should be performed in all suspected SA unless easily diagnosed by physical examination. US may be useful for OM, mainly in the diagnosis of abscess formation and surrounding soft tissue abnormalities, and it may provide guidance for diagnostic or therapeutic aspiration and/or drainage. Along with Xray, US may be performed to rule out OM, although it requires radiologic expertise and it is much less sensitive than other imaging modalities such as bone scan or MRI (76). Doppler US may provide early detection of a high vascular flow in the infected bone (10). · A disadvantage of US modality is that it cannot always differentiate between purulent and non-purulent material (77). · US may distinguish infection from other extraarticular causes of similar symptoms such as cellulitis, bursitis, appendicitis, orchitis, or psoas abscess that may lead to referred hip pain. Bone scintigraphy or scan. Technetium radionuclide scan (99mTc) is used to identify multifocal osseous involvement and to document the site of OM when local skeletal symptoms are ill defined (78). In some centres, bone scan is still faster and more accessible than MRI, but may not be ordered routinely as it involves a significant amount of radiation exposure (20,21). And although the absolute risks are small, the radiation dose* should be kept as low as possible, as guided by the clinical benefits. · OM – high sensitivity but less specificity (79), triple-phase bone scintigraphy using 99mTc-methylene diphosphonate (99mTc-MDP) can demonstrate evidence of infection as soon as 24 hours after onset and has the advantage of being able to depict multiple sites of infection (11). The specificity is lower than sensitivity, and both are lower in neonates; © ESPID 2017 – Practice Guideline – Bone and Joint Infections page 16 specificity may increase with Gallium scan or In-labelled leukocytes (80), although these techniques have more complexity and add radiation exposure to the procedure.
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