II. Definitions

  1. Osteomyelitis
    1. Inflammation of bone due to infection

III. Epidemiology

  1. Peak Incidence (age 50 to 70 years): 6.5 per 100,000 in U.S.

IV. Types

  1. Chronic Osteomyelitis (contiguous spread, 80% of cases)
    1. Typical case is a 4-6 week history of malaise, regional pain at an open wound in an adult
    2. Necrotic bone changes on presentation
    3. Vertebrae are a common site of infection in older adults
  2. Acute Osteomyelitis (hematogenous spread, 20% of cases)
    1. Typical case is a 1-2 week history of fever, Joint Pain in the long bone of a child
    2. Inflammatory bone changes on presentation

V. Classification: Waldvogel System

  1. Acute Osteomyelitis: Hematogenous Seeding
    1. Child with long bone metaphysis infection
    2. Elderly or Immunocompromised with Bone Infection
  2. Chronic Osteomyelitis: Wound associated (surgery, Trauma)
    1. Adult with open injury to bone and soft tissue
  3. Contiguous spread of infection
    1. No generalized vascular disease
    2. Generalized vascular disease

VII. Symptoms

  1. Progressive, localized musculoskeletal pain
    1. Associated erythema and edema of overlying skin
  2. Constitutional, systemic symptoms
    1. May be absent in adults (esp. Immunocompromised, Chronic Osteomyelitis)
    2. Fever (esp. Acute Osteomyelitis)
    3. Malaise
    4. Lethargy or listlessness
    5. Irritability (young children)

VIII. Signs

  1. General
    1. Exam should include a complete neurovascular evaluation of the region involved
  2. Localized erythema
  3. Soft tissue infection (e.g. Cellulitis)
  4. Poorly healing wound sites
  5. Bony tenderness
  6. Joint effusion
  7. Decreased range of motion
  8. Exposed bone
  9. Probe To Bone Test (esp. Diabetic Foot Osteomyelitis)

IX. Differential Diagnosis

  1. Cellulitis or other soft tissue infection
  2. Charcot Foot
  3. Peripheral Arterial Disease Related Chronic Skin Wound
  4. Gout
  5. Fracture
  6. Malignancy
  7. Osteonecrosis
  8. Bursitis
  9. Sickle Cell Vasoocclusive Pain Crisis
  10. SAPHO Syndrome (Synovitis, Acne, Pustulosis, Hyperostosis, Osteitis)

X. Causes

XI. Labs

  1. Inflammation markers
    1. General
      1. More useful in children, especially in ruling out Osteomyelitis (serial negative markers)
      2. Higher Test Sensitivity, but low Test Specificity
    2. Complete Blood Count (CBC)
      1. Leukocytosis
      2. Thrombocytosis
    3. Erythrocyte Sedimentation Rate (ESR) exceeds 70
      1. Test Sensitivity: 28%
    4. C-Reactive Protein (CRP) >8 mg/dl
  2. Bone Biopsy and Culture (Gold Standard)
    1. Test Sensitivity: 95%
    2. Specificity: 99%
    3. Polymicrobial infections are more common in Chronic Osteomyelitis
    4. Consider specific testing in atypical cases (e.g. Mycobacterium tuberculosis)
    5. Organism specific PCR testing
      1. Consider for rapid diagnosis or for culture while on antibiotics
    6. Variable effect on treatment
      1. Mikus (2013) J Vasc Interv Radiol 24(4): S31-2 [PubMed]
  3. Blood Culture
    1. Test Sensitivity: <50%
    2. Positive Blood Culture with clinical findings suggestive of Osteomyelitis may obviate the need for bone culture
  4. Superficial wound culture
    1. Not recommended due to contamination

XII. Imaging

  1. Approach
    1. XRay is typically performed initially as first study given in low cost, readily available
    2. MRI is preferred as a definitive study with best efficacy
    3. Alternatives when MRI contraindicated (risk of False Positives)
      1. Bone Scan with Tagged Leukocyte Scan or SPECT Scan
      2. CT
      3. PET/CT
      4. SPECT Scan
      5. Sulfur Colloid Marrow Scan
    4. Differential Diagnosis of Abnormal Imaging Findings (False Positive causes)
      1. Recent surgery or Trauma related findings
      2. Healed Osteomyelitis
      3. Arthritis
      4. Bone Neoplasm
      5. Paget Disease of Bone
      6. Peripheral Vascular Disease related poor uptake or tissue necrosis
  2. Osteomyelitis XRay
    1. First line study due to low cost and high availability
    2. Narrows differential diagnosis by ruling out other causes
    3. Typically normal in first 2-3 weeks (esp. acute Osteomyelitis in Children)
      1. Earliest findings may include soft tissue swelling, periosteal reaction
    4. Typical appearance is the "rat bite" (lytic lesions) of destroyed bony cortex
      1. Lytic changes not visualized until 50-75% of bone matrix is destroyed
  3. Osteomyelitis Bone Scan
    1. Low Test Specificity (can not distinguish Osteomyelitis from Trauma or recent post-surgical changes)
    2. Distinguishes Cellulitis from Osteomyelitis
    3. In combination with Leukocyte Scintigraphy, efficacy approaches that of MRI
      1. Consider in patients for whom MRI is contraindicated (e.g. due to Pacemaker)
  4. Osteomyelitis MRI
    1. Best Test Sensitivity and Specificity, even within first few days of infection
    2. Low Test Sensitivity in regions of surgical hardware
    3. Perform with IV Contrast
    4. Best distinguishes soft tissue infection from Bone Infection and defines infection margins
  5. Osteomyelitis PET
    1. Very high Test Sensitivity and Test Specificity, but cost prohibitive
  6. Osteomyelitis CT
    1. Avoid for Osteomyelitis evaluation unless MRI contraindicated
    2. May also identify Soft Tissue Abscess, gas formation, foreign bodies and bony destruction
  7. Bone Ultrasound
    1. May have niche applicability (e.g. Sickle Cell Disease related Osteomyelitis)
    2. May diagnosis soft tissue findings (Soft Tissue Abscess, Periostitis)
    3. Used for Ultrasound-guided needle aspiration

XIV. Complications

  1. Recurrent Infection (30% of adults with Osteomyelitis)
    1. Higher risk with prosthetic implants (require more intensive management and longer antibiotic courses)
  2. Inadequately Treated or Untreated infections
    1. Septic Arthritis
    2. Pathologic Fracture
    3. Abscess
    4. Bony abnormalities
    5. Systemic infections
    6. Contiguous soft tissue infections

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