Osteomyelitis

Osteomyelitis is an infectious process that occurs in the bone(s) (rarely occurs in multiple bones, ex. Vetebral osteomyelitis)
Review common causes of osteomyelitis

  • The classification of osteomyelitis is based on the route of entry of the organism to the bone
    • Contiguous spread of organisms from adjoining soft tissue to the bone secondary to trauma, injury surgery, etc  (if you see it was caused by a trauma think gram – or anaerobe)
    • A patient may develop bacteremia and a hematogenous bacterial emboli can be formed and lodge in the bone  (usually in the epiphyseal cartilage of long bones)
    • Kids < 4 years old
      • Most commonly S. aureus, S. pyogenes, H. influenzae
    • Kids > 4 years old
      • Most commonly S. aureus, S. pyogenes
    • Adults
      • Most commonly S. aureus, enterococcus, E. Coli, P. aeruginosa (depends on the site of infection)

Pathophysiology of osteomyelitis

  • Acute hematogenous osteomyelitis
    • Occurs primarily in kids < 15 (but adults can also get it)
      • In kids it primarily occurs in the long bones (femur, tibia, fibula, humerus)
      • In adults (50-60) it primarily occurs in the vertebrae
      • Diabetic patients are also prone to osteomyelitis resulting from diabetic foot
      • Para/quadriplegics are prone to osteomyelitis after a decubitus ulcer  (may get osteomyelitis of the vertebrae following paralysis)
    • Mainly occurs in the metaphysis of long bones
      • Blood flow gets slowed in the capillaries that make sharp hairpin turns at the metaphysis.  These capillary loops are adjacent to the epiphyseal growth plates.  By obstructing these vessels via a bacterial emboli, avascular necrosis will result.
        • As large segments of avascular bone separate & form sequestra this results in increased pressure within the bone leading to pain
      • The infection provokes an acute inflammatory response leading to decreased vascular supply resulting in tissue & bone breakdown
  • Chronic osteomyelitis may result in patients when acute osteomyelitis treatment has failed
    • Necrotic bone is present; bacterial organism isn’t rapidly multiplying but rather is lying dormant
  • Signs/symptoms (usually occur w/in 1 month of surgery or trauma)
    • PAIN at the location of the infection, fever (mainly seen in kids), increased WBCs (it’s an infection after all),  edema, erythema & tenderness are seen at the site of infection in about 50% of cases

Common antibiotic regimens used in the treatment of osteomyelitis

  • Need to do cultures & needle aspiration at the infection site or do surgical drainage to culture the bacteria
  • Treatment usually consists of surgery + antibiotics for 4-6 weeks
  • Kids < 5 years old
    • IV Vancomycin 15 mg/kg or IV Naficillin 150 mg/kg/day  or IV cefazolin 100 mg/kg/day
      • Mainly looking to cover gram + organisms
  • Kids > 5 years old
    • IV Vancomycin 15 mg/kg Q 12 hours or IV Naficillin 150 mg/kg/day  or IV cefazolin 100 mg/kg/day
      • Mainly looking to cover gram + organisms
  • Adults
    • IV Vancomycin 30 mg/kg/day +/- a fluoroquinolone (cipro or levo)
      • IV Cipro 400 mg BID or IV levo 500-750 mg QD
      • Mainly looking to cover gram + organisms, but also may want a fluoroquinolone b/c of its gram – coverage
  • Treatment of contiguous spread osteomyelitis (usually from trauma/wounds & commonly associated w/ S. aureus, P. aeruginosa, Proteus, E. Coli)
    • IV Vancomycin 15 mg/kg q 12 hours + gentamicin 5 mg/kg/day
      • Alternatives: IV naficillin 2 grams q 4-6 h +/- IV cipro 400 mg q 12 h
    • Oral therapy:  Cipro 1500 mg/day or Levo 500-750 mg/day depending on organism & antibiotic susceptibilities (separate from divalent antacids by 2 hours)
  • Treatment for chronic osteomyelitis:  1-2 months of parenteral antibiotics followed by several months of oral antibiotics (staphylococcus osteomyelitis)
  • When it’s a gram negative bacteria causing the osteomyelitis, it is most commonly Pseudomonas aeruginosa & most frequently affects the femur (metatarsals are 2nd)
    • 1/3rd of patients w/ osteomyelitis caused by a  gram negative have an underlying disease such as alcoholism or a malignancy
  • Osteomyelitis caused by anaerobic organisms is most commonly caused by Bacteroides fragilis is most often found in long bones (40%) & skull/facial bones (27%).
    • Predisposing factors:  previous fractures, diabetes, human bite wounds
    • Suspect anaerobic osteomyelitis in the presence of a foul-smelling exudate, failure to grow bacteria even when the gram stain shows the presence of organisms, see above types of injuries

Monitoring for patients with osteomyelitis:  CRP (C-reactive protein), ESR (erythrocyte sedimentation rate), renal function, CBC (WBCs, hemoglobin & hematocrit–H/H)

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