M08.026.006 Pyogenic osteomyelitis

Pyogenic osteomyelitis is a serious bone infection caused by bacteria. Understanding its causes, clinical features, diagnosis, and treatment is crucial for medical students. This section delves into the details of pyogenic osteomyelitis.

Routes of Infection

• Hematogenous Spread (Most Common): Bacteria travel through the bloodstream, seeding the bone (often the metaphysis) after bacteremia.
• Direct Inoculation: Trauma can introduce bacteria directly into the bone.
• Spread from Adjacent Infection: Infection in nearby tissues (e.g., prosthetic joint) can spread to the bone.

Points to Remember:

• Hematogenous spread is the most common route of infection in children, while direct inoculation is more frequent in adults.
• Underlying conditions like sickle cell disease and diabetes can increase susceptibility to specific bacteria.

Common Causative Organisms

• Staphylococcus aureus (S. aureus): The most frequent culprit.
• Other Important Pathogens:
  • Escherichia coli (E. coli)
  • Streptococci
  • Neisseria gonorrhoeae (gonococci)
  • Haemophilus influenzae (H. influenzae)
  • Salmonella (particularly in sickle cell disease)
  • Pseudomonas aeruginosa (common in IV drug users and diabetics)

Table 1. Summary of Common Causative Organisms in Pyogenic Osteomyelitis

Clinical Presentation

The classic triad of pyogenic osteomyelitis includes:

• Fever: Elevated body temperature.
• Leukocytosis: Increased white blood cell count, indicating infection.
• Localized Signs: Pain, redness (erythema), and swelling at the affected bone site.

Imaging Findings:

• X-rays may be normal for up to 2 weeks after infection.
• Early X-ray changes include periosteal elevation (lifting of the bone lining).
• Later findings may show lytic lesions (areas of bone destruction) surrounded by sclerosis (increased bone density).

More Sensitive Diagnostic Techniques:

• Magnetic Resonance Imaging (MRI): Provides detailed images of bone and soft tissues, aiding in earlier diagnosis.
• Nuclear Medicine Studies: Bone scans can detect increased bone activity associated with infection.

Microscopic Pathology

Microscopic examination of infected bone tissue reveals:

• Suppurative Inflammation: Presence of white blood cells (pus) indicative of infection.
• Ischemic Necrosis: Decreased blood flow can lead to bone death.

Complications of Ischemic Necrosis:

• Sequestrum: A dead piece of bone surrounded by living bone.
• Involucrum: New bone formation around the sequestrum in an attempt to wall off the infection.

Diagnosis

Confirmation of pyogenic osteomyelitis involves:

• Blood Cultures: To identify the causative organism circulating in the bloodstream.
• Bone Biopsy and Culture: Obtaining a tissue sample directly from the infected bone for definitive diagnosis.

Treatment

Pyogenic osteomyelitis requires prompt treatment with:

• Antibiotics: Administered intravenously for an extended period to eradicate the infection.
• Surgery (in some cases): Surgical drainage of pus and removal of necrotic bone may be necessary.

Complications

Despite treatment, complications can occur, including:

• Fracture: Weakened bone may be susceptible to breakage.
• Intraosseous Abscess (Brodie Abscess): Pus collection within the bone.
• Secondary Amyloidosis: Deposition of abnormal protein aggregates in organs.
• Sinus Tract Formation: Chronic draining tract at the infection site.
• Squamous Cell Carcinoma: Rarely, skin cancer can develop near a persistent draining sinus tract.
• Osteogenic Sarcoma (rare): A malignant bone tumor.

Points to Remember:

• Early diagnosis and treatment are crucial to prevent complications.
• The specific antibiotic regimen depends on the identified bacteria and its antibiotic susceptibility.

Bibliography

• [Insert relevant medical textbook on infectious diseases or orthopedic surgery]
• [Insert peer-reviewed journal article on recent advances in pyogenic osteomyelitis diagnosis or treatment]