Osteomyelitis

Basics

Description

Osteomyelitis (OM): Infection of bone with ongoing inflammatory destruction
Usually bacterial, but fungal OM does occur
Classified as acute or chronic, hematogenous, or nonhematogenous

Etiology

Hematogenous OM:
- Primarily in children, elderly, IV drug abuse (IVDA) patients
- Seeding of bacteria to bone from remote site of infection via bloodstream
- Children commonly have acute OM and adults more often subacute or chronic
- Hematogenous OM of long bones rarely occurs in adults
- Most children with acute hematogenous OM have no preceding illness
- 1/3 have history of trauma to affected area
- Staphylococcus aureus is the most common cause of OM in all ages
- Neonates: S. aureus, Enterobacteriaceae, group A and B streptococci, and Escherichia coli
- Children: S. aureus, group A streptococci, Haemophilus influenzae, Enterobacteriaceae
- Salmonella: Common in sickle cell disease
- Adults: S. aureus, Enterobacteriaceae, Pseudomonas, gram-negative rods, Staphylococcus epidermidis, gram-positive anaerobes, especially Peptostreptococcus
- Illicit drug users: Candida, Pseudomonas, Serratia marcescens
- Prolonged neutropenia: Candida, Aspergillus, Rhizopus, Blastomyces, coccidioidomycosis
Hematogenous vertebral OM:
- Uncommon
- Most prevalent in adults >45 yr
- Involves the disk and vertebra above and below
- Often in the setting of long-term urinary catheter placement, IVDA, cancer, hemodialysis, or diabetes
- IVDA: OM of pubic symphysis, sternoclavicular, and sacroiliac (SI) joints
- Lumbar vertebrae most common, followed by thoracic, then cervical
- Posterior extension leads to epidural/subdural abscess or meningitis
- Anterior extension may lead to paravertebral, retropharyngeal, mediastinal, subphrenic, retroperitoneal, or psoas abscess
Direct or contiguous OM:
- Organism(s) directly seeded in bone due to trauma, especially following open fractures:
  - Spread from adjacent site of infection or poorly healing soft tissue wound
- More common in adults and adolescents
- S. aureus, Enterobacteriaceae, Pseudomonas
- Normal vascularity:
  - S. aureus and S. epidermidis, gram-negative bacilli, and anaerobic organisms
- Vascular insufficiency/diabetes:
  - Small bones of feet are common sites
  - Infection resulting from minor trauma, infected nail beds, cellulitis, or skin ulceration
  - Polymicrobial, including anaerobes
- Puncture wound through tennis shoe: S. aureus, Pseudomonas
- Clavicular OM can occur as complication of subclavian vein catheterization
Chronic OM:
- OM that persists or recurs
- Distinguishing characteristic is necrotic bone (sequestrum) that must be débrided
- S. epidermidis, S. aureus, Pseudomonas aeruginosa, S. marcescens, and E. coli

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