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Key Features

  • S aureus is the cause of approximately 60% of all cases of osteomyelitis

  • Osteomyelitis may occur by

    • Direct inoculation (eg, from an open fracture or as a result of surgery or other procedure)

    • Extension from a contiguous focus of infection or open wound

    • Hematogenous spread (more common)

Clinical Findings

  • Acute, abrupt local symptoms and systemic toxicity; or insidious onset of vague pain over the site of infection, progressing to local tenderness and constitutional symptoms (fever, malaise, anorexia, night sweats)

  • Fever is absent in one-third or more of cases

  • Back pain

    • Often the only symptom in vertebral osteomyelitis

    • May be associated with an epidural abscess and spinal cord compression

Diagnosis

  • Isolation of S aureus from the blood (60%), bone, or a contiguous focus of a patient with symptoms and signs of focal bone infection

  • Bone biopsy and culture should be considered if blood cultures are sterile

  • Inflammatory markers (C-reactive protein, erythrocyte sedimentation rare) are typically elevated

  • Bone scan and gallium scan can identify the site of bone infection

  • Spinal infection (unlike malignancy) traverses the disk space to involve the contiguous vertebral body

  • MRI

    • Slightly less sensitive than bone scan but has a specificity of 90%

    • Indicated when epidural abscess is suspected in association with vertebral osteomyelitis

Treatment

  • Recommended antibiotic duration is 4–6 weeks or longer

  • Intravenous regimens are advised during the acute phase

    • Nafcillin or oxacillin, 9–12 g/day in six divided doses, is the drug of choice

    • Cefazolin, 2 g every 8 hours is an alternative

    • Vancomycin, 30 mg/kg/day intravenously divided in two or three doses, may be used for penicillin-allergic patients or in those with infections due to methicillin-resistant strains of S aureus

  • In patients who are responding clinically, oral step-down therapy to a rifampin combination regimen appears to be as effective; primary oral therapy may be effective but consultation with an infectious diseases specialists is recommended

  • The role of newer agents, daptomycin or linezolid, remains to be defined

  • Surgical treatment is often indicated under the following circumstances:

    • Staphylococcal osteomyelitis with associated epidural abscess and spinal cord compression

    • Other abscesses (psoas, paraspinal)

    • Extensive disease

    • Recurrent or persistent infection despite standard medical therapy

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