Chapter 120. Osteomyelitis (Part 4)

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Osteomyelitis of the thoracic spine demonstrated on a sagittal, fatsuppressed T1-weighted magnetic resonance image after the administration of IV gadolinium. At T8–T9, there is involvement of the adjacent vertebral bodies and intervening disk. Abnormally enhancing inflammatory tissue extends from the disk space anteriorly (white arrow) as well as posteriorly into the epidural space, compressing the thecal sac (black arrow). The role of diagnostic imaging in chronic osteomyelitis is to detect active infection and delineate the extent of debridement necessary to remove necrotic bone and abnormal soft tissues. CT is more sensitive than plain films for the detection of sequestra, sinus...

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Chapter 120. Osteomyelitis (Part 4) Figure 120-1
Osteomyelitis of the thoracic spine demonstrated on a sagittal, fat- suppressed T1-weighted magnetic resonance image after the administration of IV gadolinium. At T8–T9, there is involvement of the adjacent vertebral bodies and intervening disk. Abnormally enhancing inflammatory tissue extends from the disk space anteriorly (white arrow) as well as posteriorly into the epidural space, compressing the thecal sac (black arrow). The role of diagnostic imaging in chronic osteomyelitis is to detect active infection and delineate the extent of debridement necessary to remove necrotic bone and abnormal soft tissues. CT is more sensitive than plain films for the detection of sequestra, sinus tracts, and soft tissue abscesses. Both CT and ultrasound are useful for guiding percutaneous aspiration of subperiosteal and soft tissue fluid collections. Sequential technetium and gallium or indium scans may help determine whether infection is active and may distinguish infection from noninflammatory bone changes. MRI provides superior information about the anatomic extent of infection but does not always distinguish osteomyelitis from healing fractures and tumors. MRI is particularly useful in distinguishing cellulitis from osteomyelitis in the diabetic foot; however, no imaging modality consistently distinguishes infection from neuropathic osteopathy.
Appropriate samples for microbiologic studies should be obtained in all cases of suspected osteomyelitis before the initiation of antimicrobial therapy. Blood cultures are indicated in acute cases and are positive in more than one-third of cases of hematogenous osteomyelitis in children and 25% of cases of vertebral osteomyelitis in adults. The presence of sepsis occasionally requires initiation of empirical therapy after blood samples alone have been obtained for culture. If blood cultures are negative, samples from needle aspiration of pus in bone or soft tissues or from a bone biopsy should be obtained for culture; in the case of vertebral osteomyelitis, these samples can usually be obtained percutaneously with the guidance of fluoroscopy or CT. The results of culture of swabs of a sinus tract or the base of an ulcer correlate poorly with those of samples of the infected bone. For this reason, in cases of chronic osteomyelitis and contiguous-focus osteomyelitis, samples for aerobic and anaerobic culture should be obtained by percutaneous needle aspiration through uninfected tissue, percutaneous biopsy, or intraoperative biopsy at the time of surgical debridement. Coagulase-negative staphylococci and other organisms of low virulence should not automatically be disregarded as contaminants, especially in the presence of prosthetic materials. Special culture media may be necessary for the
isolation of mycobacteria, fungi, and fastidious pathogens. In some cases, histopathologic examination of biopsy specimens may be the only way to confirm a diagnosis of osteomyelitis. Osteomyelitis: Treatment Antibiotic Therapy (Table 120-2) Antibiotics should be administered only after appropriate specimens have been obtained for culture. Use of bactericidal agents has been recommended, although controlled data for this recommendation are lacking. Antibiotics should be given at a high dose; thus, for most agents, parenteral administration is required. Empirical therapy is guided by findings on Gram's staining of a specimen from the bone or abscess or is chosen to cover the most likely pathogens; such therapy should usually include high doses of an agent active against S. aureus (such as oxacillin, nafcillin, cefazolin, or vancomycin) or—if gram-negative organisms are likely to be involved—a third-generation cephalosporin, an aminoglycoside, or a fluoroquinolone. Empirical therapy should also include an agent active against anaerobes in the setting of a decubitus ulcer or diabetic foot infection.