Chapter 120. Osteomyelitis (Part 3)

MicrobiologyS. aureus is a pathogen in more than half of cases of contiguous-focus osteomyelitis. However, in contrast to hematogenous osteomyelitis, these infections are often polymicrobial and are more likely to involve gram-negative and anaerobic bacteria. Hence a mixture of staphylococci, streptococci, enteric organisms, and anaerobic bacteria may be isolated from a diabetic foot infection or pelvic osteomyelitis underlying a decubitus ulcer. Aerobic and anaerobic bacteria cause osteomyelitis following surgery or soft tissue infection of the oropharynx, paranasal sinuses, gastrointestinal tract, or female genital tract. A human bite may result in mixed infection of the hand, with anaerobes included among...
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Chapter 120. Osteomyelitis (Part 3) Chapter 120. Osteomyelitis (Part 3) Microbiology S. aureus is a pathogen in more than half of cases of contiguous-focusosteomyelitis. However, in contrast to hematogenous osteomyelitis, theseinfections are often polymicrobial and are more likely to involve gram-negativeand anaerobic bacteria. Hence a mixture of staphylococci, streptococci, entericorganisms, and anaerobic bacteria may be isolated from a diabetic foot infection orpelvic osteomyelitis underlying a decubitus ulcer. Aerobic and anaerobic bacteriacause osteomyelitis following surgery or soft tissue infection of the oropharynx,paranasal sinuses, gastrointestinal tract, or female genital tract. A human bite mayresult in mixed infection of the hand, with anaerobes included among the etiologicagents. S. aureus is the principal cause of postoperative infections; coagulase-negative staphylococci are common pathogens after implantation of orthopedicappliances; and these organisms as well as gram-negative enteric bacilli, atypicalmycobacteria, and Mycoplasma may cause sternal osteomyelitis after cardiacsurgery. Infection with P. aeruginosa is frequently associated with puncturewounds of the foot, especially when a nail passes through a sneaker, andPasteurella multocida infection commonly follows cat bites. Chronic Osteomyelitis With prompt treatment, Early diagnosis of acute osteomyelitis is critical because prompt antibiotictherapy may prevent necrosis of bone. The ESR and the CRP level are elevated inmost cases of active osteomyelitis, including those in which constitutionalsymptoms and leukocytosis are lacking. These findings are not specific toosteomyelitis, however, and the ESR is occasionally normal in early infections.Baseline values are often useful in monitoring the efficacy of treatment. A variety of radiologic tests are available for evaluation of osteomyelitis(Table 120-1). Evaluation usually begins with plain radiographs because of theirready availability, although they typically show no abnormalities during earlyinfection. Three-phase bone scans (99Tc-monodiphosphonate) offer highsensitivity but are often of low specificity, especially in the presence of underlyingbone abnormalities. There is a lack of consensus over the optimal use of otherradionuclide studies, and there is considerable variation between institutions intheir use. Use of MRI (Fig. 120-1) is expanding because of its high sensitivity andspecificity as well as its ability to demonstrate associated soft tissue abnormalities,but this modality is not available at all institutions. Table 120-1 Diagnostic Imaging Studies for Osteomyelitis Type of CommentsStudy Plain Insensitive, especially in early osteomyelitis. Mayradiographs show periosteal elevation after 10 days, lytic changes after 2–6 weeks. Useful to look for anatomic abnormalities (e.g., fractures, bony variants, or deformities), foreign bodies, and soft tissue gas. Three-phase Characteristic finding in osteomyelitis: increasedbone scan (99mTc- uptake in all three phases of scan. Highly sensitive (~95%)MDP) in acute infection; somewhat less sensitive if blood flow to bone is poor. Specificity moderate if plain films are normal, but poor in presence of neuropathic arthropathy, fractures, tumor, infarction. 67 111 111 Other Examples: Ga-citrate, In-labeled WBCs. In-radionuclide scans WBCs more specific than gallium but not always available. Often used in conjunction with bone scan because its greater 99m specificity for inflammation than Tc-MDP helps to distinguish infectious from noninfectious processes. Lack of consensus over role; often supplanted by MRI when the latter is available.Ultrasound May detect subperiosteal fluid collection or soft tissue abscess adjacent to bone, but largely supplanted by CT and MRI.CT Limited role in acute osteomyelitis. In chronic osteomyelitis, excellent for detection of sequestra, cortical destruction, soft tissue abscesses, and sinus tracts. Use limited in the presence of a metallic foreign body. ...