Osteomyelitis occurs either as a result of hematogenous seeding, contiguous spread of infection to bone from adjacent soft tissues and joints, or direct inoculation of infection into the bone as a result of trauma or surgery. Hematogenous osteomyelitis is usually monomicrobial, while osteomyelitis due to contiguous spread or direct inoculation is usually polymicrobial.
Staphylococcus aureus, coagulase-negative staphylococci, and aerobic gram-negative bacilli are the most common organisms; other pathogens including streptococci, enterococci, anaerobes, fungi, and mycobacteria have also been implicated.
Acute osteomyelitis typically presents with gradual onset of pain over several days. Local findings (tenderness, warmth, erythema, and swelling) and systemic symptoms (fever, rigors) may also be present. Chronic osteomyelitis tends to occur in the setting of previous osteomyelitis and presents with recurrent pain, erythema, or swelling, sometimes in association with a draining sinus tract.
Most cases of diabetic foot osteomyelitis occur in the setting of ulcers that develop in the absence of exposed bone. If a diabetic foot ulcer is larger than 2 x 2 cm or bone is palpable, osteomyelitis is so likely that additional noninvasive evaluation may not be needed. Positive results of a probe-to-bone test are sufficient for diagnosis of osteomyelitis.
Establishing an accurate diagnosis of osteomyelitis is critical, since the infection can require prolonged antibiotic therapy and/or aggressive surgical intervention. An integrated diagnostic approach incorporating the various diagnostic tools is outlined in detail above.
The reference standard for diagnosis of osteomyelitis is isolation of bacteria from a bone biopsy sample obtained via sterile technique, together with histologic findings of inflammation and osteonecrosis. Bone biopsy may not be needed for patients with radiologic studies consistent with osteomyelitis in the setting of positive blood cultures. Cultures obtained from sinus tract drainage are not reliable.
Open biopsy is preferable over needle biopsy; bone samples should be obtained at the time of surgical debridement if performed. Percutaneous needle biopsy is an alternative to open biopsy; ideally, it should be performed via intact tissues and under radiographic guidance to optimize yield. Bone biopsy should be obtained prior to treatment with antimicrobial therapy whenever possible.
Leukocytosis may be observed in the setting of acute osteomyelitis but is less common in the setting of chronic osteomyelitis. The erythrocyte sedimentation rate and/or C-reactive protein are usually elevated but may be normal. Blood cultures are most likely to be positive in the setting of hematogenous infection and vertebral disease; positive blood cultures may obviate the need for invasive diagnostic testing.
Treatment of osteomyelitis often requires both surgical debridement of necrotic material and antimicrobial therapy for eradication of infection. The optimal duration of antibiotic therapy is not certain; we suggest continuing parenteral antimicrobial therapy at least six weeks from the last debridement (Grade 2B). Suggested antibiotic regimens are outlined in the Table．
- MSSA : CEZ 1 g intravenously every 8 hours
- MRSA : Vancomycin 30 mg/kg intravenously every 24 hours in two equally divided doses; not to exceed 2 g/24 hours unless concentrations in serum are inappropriately low
- Coagulase-negative staphylococci : Vancomycin 30 mg/kg intravenously every 24 hours in two equally divided doses; not to exceed 2 g/24 hours unless concentrations in serum are inappropriately low
- Gram-negative organisms (including Pseudomonas): Ciprofloxacin 750 mg orally twice daily. LVFX 750 mg orally once daily. Ceftazidime 2 g intravenously every 8 hours. Cefepime 2 g intravenously every 12 hours
- Empiric therapy Vancomycin PLUS an agent with activity against gram-negative organisms