osteomyelitis

Introduction

Infection of the bone. (also see chronic osteomyelitis)

Classification

• acute hematogenous osteomyelitis
  • infection of intervertebral disc space & 2 adjacent vertebrae
• contiguous focus osteomyelitis
  • patients > 50 years of age with diabetes mellitus or peripheral vascular disease
  • secondary spread of infection from adjacent soft tissue or joints, or due to surgery or trauma
  • rheumatoid arthritis
• sternal osteomyelitis
  • wound healing complications
  • unstable sternum
  • fever after thoracic surgery
• clavicular osteomyelitis
  • pain, cellulitis, or drainage in the sternoclavicular area after subclavian vein catheterization
• sternoclavicular joint osteomyelitis
  • pain & fever in an injection drug user

Etiology

• Staphylococcus aureus & coagulase-negative staphylococci are the most common pathogens
• gram-negative rods (Pseudomonas, Serratia, Salmonella, E. coli)
  • Pseudomonas aeruginosa is a common cause of osteomyelitis in a patient who has stepped on a nail while wearing a tennis shoe & in injection drug users
  • Salmonella &/or S aureus in patients with sickle cell disease
• anaerobes
• polymicrobial infection may occur in the setting of diabetic foot ulcer & other forms of contiguous focus osteomyelitis
• infection of intervertebral disk space & adjacent vertebrae from hematogenous spread (S aureus)
• sternal osteomyelitis after thoracic surgery
• sternoclavicular joint osteomyelitis in injection drug users
• less frequent causes
  • tuberculosis, brucellosis, histoplasmosis, coccidioidomycosis, blastomycosis
• risk factors for hematogenous osteomyelitis
  • hemodialysis with tunneled intravascular catheters
  • long-term intravascular catheters
  • high-grade bacteremia
  • endocarditis
  • sickle cell disease

Pathology

• microorganisms enter the bone by hematogenous spread (S aureus) or directly via a wound or from an adjacent infection (polymicrobial) or from surgery or trauma (polymicrobial)
• the metaphyses of long bones (tibia, femur, humerus) & vertebrae are the most frequently involved sites in children
• in adults, the vertebrae, sternum, clavicle, sacrum, ilium & metaphyses of long bones (tibia, femur, humerus) are most commonly affected
• in older adults, the vertebrae are most commonly affected
• bones of the foot in patients with diabetic foot ulcers
• infection may traverse cortical bone to involve the marrow

Clinical manifestations

• presentation is generally subacute
  • pressure ulcer or diabetic foot ulcer not responding to 6 weeks of therapy
  • dull pain from the infected bone
  • local erythema, warmth, edema
  • palpable tenderness
  • fever may or may not be present
• 50% of patients present with vague pain of the affected limb, back or neck
• in vertebral osteomyelitis, pain is secondary to nerve root irritation
• pain may be present for 1-3 months with little or no fever
• children may present with acute onset of fever, irritability,lethargy & local inflammation of < 3 weeks duration
• findings on physical exam with chronic osteomyelitis
  • point tenderness, muscle spasm, & draining sinus
  • sinus tract overlying a bone
  • purulent, serous or serosangineous discharge
  • draining sinus tract is pathognomonic for chronic osteomyelitis
  • foot ulcer with exposed bone
  • positive probe-to-bone test
• findings that predict contiguous osteomyelitis
  • ulcer present for >= 2 weeks
  • ulcer size > 2 cm
  • visible bone or ability to probe bone

Laboratory

• complete blood count (CBC)
• culture:
  • blood culture for suspected osteomyelitis
    • positive in > 50% of patients
  • needle aspiration of pus from bone
  • bone biopsy: gold standard
    • biopsy through uninvolved skin (if associated with wound)
    • diagnosis via imaging (X-ray, MRI, PET) prior to bone biopsy if bone not clearly visible through wound
    • CT-guided percutaneous needle biopsy for vertebral osteomyelitis
    • bone biopsy not necessary if blood culture is positive for typical pathogen
  • sinus tract & wound drainage cultures not useful
  • it is not possible to predict the etiologic agent based upon epidemiology, thus cultures are essential to direct antibiotic therapy
• ESR > 100 mm/hour is confirmatory, ESR > 70 mm/hr is predictive, but ESR is variable & may not be elevated
• see ARUP consult

Radiology

• confirm diagnosis & extent of disease with imaging prior to bone biopsy
• plain films may confirm diagnosis of osteomyelitis in most patients
  • recommended as intital imaging test (specificity > sensitivity)
  • plain films are not positive for at least 10 days,
  • lytic lesions may not be visible for 2-6 weeks
  • bone sequestration or bone callus suggest chronic osteomyelitis
  • ref seems to disagree with ref regarding relative cost-effectiveness of plain radiographs vs MRI
• magnetic resonance imaging (MRI)[4,8,26]
  • imaging modality of choice
  • may be positive early (T1 & T2 images)
  • may aid in localization of lesions & demonstration of sequestra
  • more sensitive (90%) & specific (80%) than CT
  • with gadolinium enhancement, identification of epidural abscess
  • not useful for following treatment response
    • follow-up MRI limited to patients who do not improve with therapy
  • not necessary in setting of chronic draining sinus tract
  • able to detect sinus tracts
  • particularly poor at differentiating osteomyelitis from benign postoperative marrow edema & from marrow edema due to Charcot arthropathy
• computed tomography (CT)
  • imaging modality of choice when MRI cannot be performed
  • soft tissue swelling around affected bone
  • later, erosive changes in the bone are seen
  • CT-guided percutaneous needle biopsy if suspected vertebral osteomyelitis with negative blood cultures
• radionuclide bone scan
  • may be positive within 2 days of infection
  • high negative predictive value if perfusion is adequate
  • non-specific (specificity 25%), MRI & CT more useful
  • recent surgery at the site renders bone scan less useful
• positron-emission tomography (PET)
  • highest sensitivity (96%) & specificity (91%) for confirming osteomyelitis
  • most expensive imaging
  • availability limited

Management

• < 5% of patients receiving prompt treatment progress to chronic osteomyelitis
• empiric antibiotics
  • broad-spectrum empiric antibiotics for sepsis
    • vancomycin + piperacillin tazobactam or cefepime
    • bone biopsy for culture & debridement of necrotic tissue important but should not delay empiric antibiotics
  • in the absence of sepsis, consider withholding antibiotics until after bone biopsy for culture & debridement of necrotic tissue
• duration of antibiotic therapy
  • 4-6 weeks of IV antibiotics are indicated for acute hematogenous osteomyelitis; may require longer
  • 4-6 weeks of IV antibiotics in addition to surgical debridement for contiguous focus osteomyelitis or chronic osteomyelitis
    • 6 weeks for diabetes-associated osteomyelitis
    • prolonged therapy if residual necrotic bone
  • oral antibiotics non-inferior to IV antibiotics
  • if infected bone has been completely removed, antibiotics may be discontinued after wound has adequately healed
  • a 90-day course of antibiotics compares favorably with surgery (removal of infected bone without amputation) followed by 10 days of antibiotics in selected patients with diabetic foot osteomyelitis
  • 6 weeks of antibiotics non-inferior to 12 weeks
• initial empiric antibiotics
  • vancomycin + piperacillin tazobactam
  • nafcillin 2 g IV every 4 hours or cefazolin 2 g IV every 8 hours plus rifampin
  • 3rd generation cephalosporin if suspecting gram negative rod
  • osteomyelitis in patients with diabetic foot ulcer
    • vancomycin + piperacillin tazobactam
    • vancomycin plus meropenem
    • beta-lactam/beta-lactamase inhibitor
    • 3rd generation cephalosporin or 4th generation cephalosporin plus metronidazole (too narrow)
    • adjunctive rifampin therapy improves outcomes in treatment of diabetic foot osteomyelitis
  • add rifampin if orthopedic hardware cannot be removed
• antibiotic agents for specific pathogens
  • oral antibiotics non-inferior to IV antibiotics
  • Staphylococcus aureus or empiric therapy:
    • nafcillin 2 g every 4 hours or cefazolin 2 g every 8 hours
      • cefazolin superior to nafcillin or oxacillin
      • add rifampin if orthopedic hardware cannot be removed
    • clindamycin or vancomycin are alternatives
    • vancomycin 1 g IV every 12 hours for MRSA
  • Streptococci
    • penicillin G 4 million units every 6 hours
    • ceftriaxone 2 g every 24 hours clindamycin & vancomycin are alternatives
  • Enteric gram-negative organisms:
    • ceftriaxone 1 g every 12 hours, or other 3rd generation cephalosporin
    • Ciprofloxacin 750 mg PO every 12 hours if sensitivity permits
  • Pseudomonas aeruginosa or Serratia
    • ceftazidime 2 g IV every 8 hours plus gentamicin twice a week
    • alternatives imipenem 500 mg IV every 6 hours or Cefepime or Zosyn plus aminoglycoside twice a week
  • anaerobes
    • clindamycin
    • Unasyn 2 g IV every 8 hours or Flagyl 750 mg IV every 8 hours {alternatives}
  • mixed aerobe/anaerobe
    • Unasyn
    • Imipenem
• surgery
  • bone or joint destruction may be indication for surgery
  • debridement should be considered if there is poor response to therapy within 48 hours, or if there is undrained pus (abscess) or septic arthritis
  • chronic osteomyelitis requires complete drainage, debridement of sequestra, & removal of any prosthetic material in addition to 4-6 weeks of antibiotics based on culture of bone (also see chronic osteomyelitis)
  • revascularization for poor arterial supply (limb ischemia)
    • amputation for critical ischemia not amenable to revascularization
      • residual bone biopsy cultures may overestimate histologically confirmed residual osteomyelitis after forefoot amputation
  • primary wound closure is contraindicated
  • selected cases of diabetic foot osteomyelitis may be treated without surgery
• hyperbaric oxygen as adjunctive therapy in post-traumatic or chronic osteomyelitis
• skin flaps & bone grafts may facilitate healing
• hardware-related osteomyelitis
  • for most patients, orthopedic hardware should be removed with surgical debridement of infected bone
  • if symptoms last < 1 month, surgical debridement with retention of hardware plus 3-6 months of antibiotic therapywith a fluoroquinolone + rifampin
• chronic osteomyelitis can be treated with oral agents

More general terms

• bone disease; osteopathia
• bacterial infection

More specific terms

• ankle/foot osteomyelitis
• chronic osteomyelitis
• femur osteomyelitis
• hand osteomyelitis
• pelvis/hip osteomyelitis
• petrotitis; petrous apicitis; Gradenigo's syndrome
• sacroiliac osteomyelitis
• tibia/fibula osteomyelitis
• vertebral osteomyelitis