Osteomyelitis

Osteomyelitis is an infection of the bone and bone marrow, characterized by the presence of inflammatory bone tissue due to infectious agents. It can occur as an acute or chronic condition and may affect any bone in the body.

Epidemiology

• Incidence: The annual incidence of osteomyelitis in the general population is approximately 2 to 20 cases per 100,000 individuals, with higher rates observed in specific populations.
• Demographics:
  • More common in males than females (2:1 ratio).
  • Higher incidence in children and adults over the age of 50.

Etiology

Osteomyelitis can result from various infectious agents, including bacteria, fungi, and mycobacteria. The most common causative organisms are:

1. Bacterial Pathogens:
   • Staphylococcus aureus: The most frequent pathogen, including methicillin-resistant Staphylococcus aureus (MRSA).
   • Streptococcus species: Especially in cases associated with trauma or surgery.
   • Gram-negative bacilli: Such as Escherichia coli, particularly in patients with certain risk factors (e.g., diabetes, urinary tract infections).
   • Pseudomonas aeruginosa: Common in patients with puncture wounds or intravenous drug use.
2. Fungal Pathogens:
   • Candida species and other fungi can cause osteomyelitis, particularly in immunocompromised patients.
3. Mycobacterial Pathogens:
   • Mycobacterium tuberculosis: Can cause a specific form known as Pott’s disease, which primarily affects the vertebrae.

Pathophysiology

• Route of Infection: Osteomyelitis can occur through various routes:
  1. Hematogenous Spread: Bacteria spread from distant sites through the bloodstream, commonly affecting children and patients with underlying health conditions.
  2. Contiguous Spread: Infection spreads from adjacent soft tissue or joint infections, often seen in adults with diabetic foot ulcers or pressure sores.
  3. Direct Inoculation: Occurs due to trauma, surgery, or fractures, leading to direct contamination of the bone.
• Bone Response: The infection triggers an inflammatory response in the bone, leading to:
  • Increased osteoclast activity and bone resorption.
  • Formation of a subperiosteal abscess or intramedullary abscess.
  • Formation of necrotic bone (sequestrum) surrounded by viable bone (involucrum).

Clinical Features

1. Acute Osteomyelitis:
   • Symptoms: Sudden onset of fever, chills, localized pain, swelling, redness, and tenderness over the affected bone.
   • Signs: Possible drainage of pus or a fluctuating swelling over the affected area; systemic signs of infection may be present.
2. Chronic Osteomyelitis:
   • Symptoms: Persistent or recurrent localized pain, swelling, and discharge (often from a sinus tract).
   • Signs: Presence of necrotic tissue, sinus tracts, and chronic inflammation; systemic symptoms may be less prominent than in acute cases.

Diagnosis

1. Clinical Evaluation:
   • History and physical examination to assess risk factors, symptoms, and signs of infection.
2. Imaging Studies:
   • X-rays: May show bone destruction or new bone formation, but often not visible until 10-14 days after the onset of infection.
   • MRI: The gold standard for early detection, showing marrow edema, abscess formation, and soft tissue involvement.
   • CT Scans: Useful for assessing complex anatomy and detecting sequestra.
   • Bone Scintigraphy: Can detect osteomyelitis but is not specific and may show false positives.
3. Microbiological Studies:
   • Bone Aspiration: Obtaining pus or bone for culture and sensitivity testing is critical for identifying the causative organism.
   • Blood Cultures: May be positive in cases of hematogenous osteomyelitis.
4. Laboratory Tests:
   • Complete Blood Count (CBC): May show leukocytosis.
   • Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP): Elevated in response to infection.

Management

Acute Osteomyelitis

1. Antibiotic Therapy:
   • Empirical intravenous antibiotics should be initiated promptly, adjusted based on culture results.
   • Common regimens include:
     • Staphylococcus aureus: Nafcillin or oxacillin; consider vancomycin for MRSA coverage.
     • Gram-negative organisms: Piperacillin-tazobactam or ceftriaxone.
     • Duration of therapy is typically 4 to 6 weeks, depending on clinical response.
2. Surgical Intervention:
   • Surgical drainage of abscesses or debridement of necrotic bone may be necessary.
   • In cases of chronic osteomyelitis, extensive debridement may be required to remove infected and devitalized tissue.

Chronic Osteomyelitis

1. Long-Term Antibiotic Therapy:
   • Antibiotic treatment may extend for 6 to 12 weeks, often requiring oral antibiotics after initial IV therapy.
2. Surgical Management:
   • Complete removal of necrotic tissue (sequestrectomy) and stabilization of the affected bone.
   • Use of bone grafts or bioactive materials to promote bone healing.

Complications

1. Local Complications:
   • Chronic pain, deformity, or disability.
   • Development of chronic osteomyelitis with persistent infection.
2. Systemic Complications:
   • Sepsis: A severe systemic response to infection can lead to multi-organ failure.
   • Pathologic fractures due to weakened bone.

Prognosis

• The prognosis for osteomyelitis varies depending on factors such as the duration of the infection, the presence of comorbid conditions, the causative organism, and the response to treatment.
• Early diagnosis and appropriate management improve outcomes significantly, while delayed treatment can lead to chronic infection and complications.