Osteomyelitis

Epidemiology

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• Hematogenous osteomyelitis
  • More common in children and adolescents
  • Incidence is increasing in adults, driven by a rise in vertebral osteomyelitis
• Exogenous osteomyelitis: more common in adults

Etiology

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Routes of infection

• Hematogenous osteomyelitis (endogenous osteomyelitis): caused by hematogenous dissemination of a pathogen
• Exogenous osteomyelitis: caused by a spread of bacteria (typically multiple pathogens) from the surrounding environment
  • Posttraumatic: infection following deep injury (penetrating injury, open fractures, severe soft tissue injury)
  • Contiguous: spread of infection from adjacent tissue
    • Secondary to infected foot ulcer in patients with diabetes
    • Iatrogenic (e.g., postoperative infection of a prosthetic joint implant)

Pathogen

• Overall: Staphylococcus aureus
• Sexually active young adults: Neisseria gonorrhoeae (presents as septic arthritis, tenosynovitis, dermatitis).
• Sickle cell disease: Salmonella species, S. aureus. c
• IV drug users (IVDU): Pseudomonas aeruginosa, Candida, S. aureus (often involves vertebral spine, clavicle).
• Prosthetic joint/hardware: Staphylococcus epidermidis.
• Puncture wound through shoe: Pseudomonas aeruginosa. c
  • P. aeruginosa thrives in warm, moist, hydrophobic environments—specifically the foam/rubber inner soles of athletic shoes (sneakers).
• Cat/dog bites: Pasteurella multocida.
• Diabetic foot ulcer (polymicrobial): S. aureus, Gram-negatives, anaerobes.
• Vertebral osteomyelitis (Pott disease): Mycobacterium tuberculosis.

Pathophysiology

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Clinical features

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Diagnostics

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• Initial / Screening Labs: ESR & CRP (highly sensitive; CRP tracks response to Tx). CBC (leukocytosis w/ left shift).
• Initial Imaging: Plain Radiographs (X-ray).
  • May be normal in early disease (first 10-14 days).
  • Early changes: Soft tissue swelling, periosteal reaction/elevation.
  • Late changes: Cortical erosion, lytic bone lesions, sequestrum (necrotic bone fragment), involucrum (thick layer of new periosteal bone).
• Most Sensitive Imaging: MRI w/ gadolinium (best test for early detection, soft tissue/epidural involvement; indicated if X-ray is negative but clinical suspicion remains high).
• Confirmatory / Gold Standard: Bone biopsy and culture (CT-guided needle biopsy or open surgical biopsy).
  • Must perform before initiating Abx unless pt is hemodynamically unstable or septic.
  • Superficial wound/sinus tract swabs are unreliable (reflect skin flora; exception: S. aureus).

Treatment

1. Obtain Diagnostic Samples: Bone biopsy/culture prior to Abx initiation (unless septic/unstable).
2. Empiric Antibiotics (broad-spectrum, prolonged IV 4-6 weeks):
   • Standard empiric: Vancomycin (MRSA coverage) + 3rd/4th-gen Cephalosporin (e.g., Cefepime) OR Piperacillin-Tazobactam (Gram-negative & anaerobic coverage).
   • Sickle cell: Coverage for Salmonella & S. aureus (e.g., Ceftriaxone + Vancomycin). c
   • Puncture wound (shoe): Coverage for Pseudomonas (e.g., Cefepime or Ciprofloxacin).
3. Targeted Antibiotics: De-escalate based on bone culture & sensitivity results.
4. Surgical Intervention: Surgical debridement indicated for sequestrum removal, sinus tract excision, intraosseous/subperiosteal abscess, or failure to respond to Abx.
5. Monitoring: Serial CRP/ESR levels to track response to therapy.