|Print Date:||May 19, 2013, 7:58 am|
|Title||Acute on chronic osteomyelitis
Post-traumatic changes with deformity after trauma
|Text||Osteomyelitis, an infectious process that produces bony destruction, can be limited to a single area of bone or can involve multiple areas, including the marrow, cortex, periosteum, and surrounding soft tissue. Osteomyelitis may spread by a hematogenous route, from a contiguous contaminated source (e.g. following trauma, bone surgery, or joint replacement), or be a complication of vascular insufficiency (predominantly in diabetic patients). Staphylococcus aureus is by far the common pathogen causing osteomyelitis. The infection may be acute or chronic; acute infections tend to evolve over several days to weeks. Acute infection may resolve with appropriate treatment. Osteomyelitis that is untreated or insufficiently treated may give rise to a chronic infection which may be characterized by a sequestrum (necrotic bone, bacteria, and granulation tissue that have been walled off by new reactive bone or fibrous tissue). Chronic osteomyelitis is also characterized by the persistence of microorganisms, low-grade inflammation, and fistulous tracts. Recurrent osteomyelitis in the same area along with the presence of fever is indicative of a chronic infection. The diagnosis of osteomyelitis is based on clinical, laboratory, and imaging findings, and when possible, identification of the offending organism by blood culture or direct bone biopsy.
Plain radiographs should be the first imaging modality for evaluating osteomyelitis. Initially they may be normal or only show periosteal reaction and soft tissue swelling. Bone destruction (osteolytic foci on the radiographs) may not be visible until 10-21 days after the infection has begun. With chronicity, reactive osteosclerosis as well as areas of osteolysis and sequestra and involucra may occur. Differentiation of acute osteomyelitis from inactive chronic osteomyelitis can be difficult, but certain indications on the radiograph aid in distinguishing between the two, including a change from a previous radiograph, poorly defined areas of osteolysis, and thin and linear periostitis. Although CT is useful for evaluating cortical destruction, sequestration, cloacae, and bone and soft tissue abscesses, MR imaging (T1-weighted, T2-weighted with fat sat and post contrast sequences) is the best modality for evaluating osteomyelitis, cellulitis and areas of necrosis for debridement. Tc 99m â€“bone scintigraphy may also be useful for diagnosing osteomyelitis but does not have the resolution of MRI. Dual isotope bone-granulocyte scintigraphy (Tc 99m MDP)bone and white blood cells labeled with Indium-111) has a high sensitivity (84%) and specificity (71%) in detecting areas of acute infection. However, MRI has increased sensitivity and accuracy in the detection of osteomyelitis as compared to three-phase bone scintigraphy. In cases of acute osteomyelitis, the process is identified as area(s) of low signal intensity on T1-weighted images and high signal intensity images in the medullary canal on fat-saturated T2-weighted MR images or STIR (short tau inversion recovery) MR images. Cellulitis shows similar findings (low-signal-intensity foci on T1-weighted MR images and high-signal-intensity foci on fat-saturated T2-weighted or STIR MR images). Contrast-enhanced T1-weighted MR imaging shows not only the enhancement of areas of osteomyelitis and cellulitis, but also shows non-enhancing areas of necrosis important for debridement. Active and inactive phases of osteomyelitis may be differentiated by periosteal bone formation with subperiosteal fluid and by areas of high signal intensity areas on T2-weighted and STIR MR images that enhance after contrast media. Bone sclerosis is low signal intensity on MR sequences. Abscesses and tracts can also be demonstrated on MRI. For definitive histologic diagnosis, fluoroscopy and/or CT is used to biopsy appendicular and axial lesions and fluoroscopy can be sometimes use for biopsying appendicular lesions. Deep abscesses can be drained with CT guidance and superficial abscesses with sonographic or CT guidance.
|References:||(1) Lew, DP, Waldvogel, FA. Osteomyelitis. Lancet 2004; 364:369-79
(2) Resnick, D. Osteomyelitis, Septic Arthritis, and Soft Tissue Infection: Mechanisms and Situations. Diagnosis of Bone and Joint Disorders. WB Saunders, Philadelphia 2002. pp 2377-2480.
(3) Buhl, T, Stentzer, K, Hede, A, Kjaer, A, Hesse, B. Bone infection in patients suspected of complicating osteomyelitis: the diagnostic value of dual isotope bone-granulocyte scintigraphy. Clin Physiol Funct Imaging 2005; 25:20-26.
|Contributor||Russell A. Patterson (Uniformed Services University)|
|Author||Paul F. Haggerty|
|Peer Reviewer||Lorraine G. Shapeero, M.D. (Uniformed Services University)|
|Record Number||: 6708|
|Category:||Clinical Exam Finding or Sign|
|Location:||MSK - Musculoskeletal|
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