Chapter 120. Osteomyelitis (Part 4)

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) 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 IVgadolinium. At T8–T9, there is involvement of the adjacent vertebral bodies andintervening disk. Abnormally enhancing inflammatory tissue extends from thedisk 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 activeinfection and delineate the extent of debridement necessary to remove necroticbone and abnormal soft tissues. CT is more sensitive than plain films for thedetection of sequestra, sinus tracts, and soft tissue abscesses. Both CT andultrasound are useful for guiding percutaneous aspiration of subperiosteal and softtissue fluid collections. Sequential technetium and gallium or indium scans mayhelp determine whether infection is active and may distinguish infection fromnoninflammatory bone changes. MRI provides superior information about theanatomic extent of infection but does not always distinguish osteomyelitis fromhealing fractures and tumors. MRI is particularly useful in distinguishing cellulitisfrom osteomyelitis in the diabetic foot; however, no imaging modality consistentlydistinguishes infection from neuropathic osteopathy. Appropriate samples for microbiologic studies should be obtained in allcases of suspected osteomyelitis before the initiation of antimicrobial therapy.Blood cultures are indicated in acute cases and are positive in more than one-thirdof cases of hematogenous osteomyelitis in children and 25% of cases of vertebralosteomyelitis in adults. The presence of sepsis occasionally requires initiation of empirical therapyafter blood samples alone have been obtained for culture. If blood cultures arenegative, samples from needle aspiration of pus in bone or soft tissues or from abone biopsy should be obtained for culture; in the case of vertebral osteomyelitis,these samples can usually be obtained percutaneously with the guidance offluoroscopy or CT. The results of culture of swabs of a sinus tract or the base of an ulcercorrelate poorly with those of samples of the infected bone. For this reason, incases of chronic osteomyelitis and contiguous-focus osteomyelitis, samples foraerobic and anaerobic culture should be obtained by percutaneous needleaspiration through uninfected tissue, percutaneous biopsy, or intraoperative biopsyat the time of surgical debridement. Coagulase-negative staphylococci and other organisms of low virulenceshould not automatically be disregarded as contaminants, especially in thepresence of prosthetic materials. Special culture media may be necessary for theisolation of mycobacteria, fungi, and fastidious pathogens. In some cases,histopathologic examination of biopsy specimens may be the only way to confirma diagnosis of osteomyelitis. Osteomyelitis: Treatment Antibiotic Therapy (Table 120-2) Antibiotics should be administered only after appropriatespecimens have been obtained for culture. Use of bactericidal agents has beenrecommended, although controlled data for this recommendation are lacking.Antibiotics should be given at a high dose; thus, for most agents, parenteraladministration is required. Empirical therapy is guided by findings on Grams staining of a specimenfrom the bone or abscess or is chosen to cover the most likely pathogens; suchtherapy should usually include high doses of an agent active against S. aureus(such as oxacillin, nafcillin, cefazolin, or vancomycin) or—if gram-negativeorganisms are likely to be involved—a third-generation cephalosporin, anaminoglycoside, or a fluoroquinolone. Empirical therapy should also include anagent active against anaerobes in the setting of a decubitus ulcer or diabetic footinfection.