Definition
Osteomyelitis is an inflammatory process of the bone marrow and adjacent bone, caused most commonly by bacterial infection.
It can be:
- Acute – sudden onset with rapid progression
- Chronic – long-standing infection with recurrent flares
Etiology and Classification
1. Acute Hematogenous Osteomyelitis
Infection reaches the bone via bloodstream from a distant source
Most common form in children
90% of cases: caused by Streptococcus pyogenes
Common sources: furuncle, carbuncle, sore throat, dental abscess, phlegmon
Pathogenesis
- Bacteria enter circulation → lodge in the metaphysis of long bones (esp. femur in 70–80%)
- Due to slow blood flow and high vascularity, infection establishes easily
- Inflammatory response → suppuration (pus formation)
- Infection spreads to:
- Bone marrow → medullary hypertension
- Haversian canals → cortical bone
- Periosteum → subperiosteal abscess
- If untreated:
- Bone necrosis → sequestrum formation (dead bone)
- Fistula formation → drains pus externally
- Phlegmon of surrounding soft tissue
- Bacteria may spread to bloodstream → septicemia
Key Clinical Insight: Suppuration in a rigid bone compartment leads to vascular compression → necrosis and chronicity.
2. Acute Post-Traumatic Osteomyelitis
Caused by direct inoculation of bacteria into the bone (e.g., open fractures, surgical wounds)
Early fistula formation connecting bone to skin
Infection starts in periosteum and compact bone, later spreading to marrow
3. Chronic Osteomyelitis
Can evolve from untreated or partially treated acute osteomyelitis
Characterized by:
- Persistent sequestrum (necrotic bone)
- Unobliterated cavities surrounded by sclerotic bone
- Formation of fistulas with chronic purulent drainage
Risk: Chronic inflammation → may transform into epidermoid carcinoma