Description

• An acute or chronic bone infection with associated inflammation; can occur as a result of hematogenous seeding, contiguous spread of infection, or direct inoculation into intact bone (trauma or surgery)
• Two major classification systems:
  • Lew and Waldvogel classification: classified according to duration (acute or chronic) and source of infection (hematogenous or contiguous)
  • Cierny-Mader classification: based on the portion of bone affected, physiologic status of the host, and risk factors
• Special situations
  • Vertebral osteomyelitis
    • Results from hematogenous seeding (most common), direct inoculation, or contiguous spread; back pain is the most common initial symptom. Lumbar spine is the most commonly involved, followed by thoracic spine.
  • Prosthetic joint infections
    • X-ray and three-phase bone scan; MRI/CT is of limited use with prostheses.
  • Posttraumatic infections
    • Risk factors include type and severity of fracture as well as contamination. Tibia is the most common location.

Epidemiology

• More common in older adults; predominant sex: male > female
• Hematogenous osteomyelitis
  • Adults (mostly >50 years of age): vertebral
  • Children: long bones
• Contiguous osteomyelitis: related to diabetic foot infections (DFIs), decubitus ulcers, and infected total joint arthroplasties in older adults; trauma and surgery in younger adults
• Mycobacterium tuberculosis (MTB) is the most common cause of vertebral osteomyelitis worldwide. It is more likely to involve multiple vertebral bodies—especially of the thoracic spine—and is associated with paraspinal abscess formation.

Incidence
Generally low; normal bone is resistant to infection. The incidence of vertebral osteomyelitis has been estimated at 2.4 cases per 100,000 population, with an increasing incidence with advancing age.

Prevalence
Up to 66% of diabetics with foot ulcerations

Etiology and Pathophysiology

• Acute: suppurative infection of bone with edema and vascular compromise leading to sequestrum (segments of necrotic bone, may contain pus)
• Chronic: presence of necrotic bone or sequestrum or recurrence of previous infection
• Hematogenous osteomyelitis (typically monomicrobial)
  • Staphylococcus aureus (most common); coagulase-negative staphylococci and aerobic gram-negative bacteria; Pseudomonas aeruginosa (intravenous [IV] drug user); Salmonella sp. (sickle cell disease); MTB and fungal (rare; in endemic areas or in immunocompromised hosts)
• Contiguous focus osteomyelitis (polymicrobial)
  • Diabetes or vascular insufficiency
    • Coagulase-positive and coagulase-negative staphylococci; streptococci, gram-negative bacilli, anaerobes (Peptostreptococcus sp.)
  • Sacral decubitus ulcer
    • Pressure-related skin ulceration and necrosis
  • Puncture wound through shoe
    • P. aeruginosa
• Prosthetic device
  • Coagulase-negative staphylococci and S. aureus

Risk Factors

• Diabetes mellitus (particularly, diabetic foot ulcer); recent trauma/surgery; foreign body (e.g., prosthetic implant)
• Neuropathy and vascular insufficiency; immunosuppression (including dialysis); sickle cell disease; injection drug use; previous osteomyelitis; bacteremia

General Prevention

• Comprehensive annual foot exam for diabetic patients; screen for peripheral artery disease; optimize glycemic control in diabetes.
• Antibiotic prophylaxis for posttraumatic infection
  • Clean bone surgery
    • Administer IV antibiotics within an hour of skin incision, keep at therapeutic level throughout surgery, and continue ≤24 hours postprocedure.
  • Closed fractures
    • Cefazolin, cefuroxime, clindamycin (β-lactam allergy), or vancomycin (β-lactam allergy or MRSA infection)
  • Open fractures
    • In patients who can receive antibiotics within 3 hours of injury with prompt operative treatment, 1st-generation cephalosporins are preferred (clindamycin or vancomycin if allergic); ceftriaxone for type III fractures; add metronidazole if associated with soil or fecal matter contamination.