Osteomyelitis is most commonly caused by bacterial infection, with Staphylococcus aureus being the primary culprit.
Here's a breakdown of the causes:
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Bacterial Infection:
- Staphylococcus aureus: This is the most frequent cause, often originating from skin infections or nasal carriage.
- Other bacteria: Streptococcus species, E. coli, Pseudomonas, and Klebsiella can also cause osteomyelitis, particularly in specific patient populations (e.g., intravenous drug users, individuals with sickle cell disease).
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Mechanism of Infection: Germs can reach the bone through various routes:
- Bloodstream (Hematogenous): Bacteria travel through the bloodstream from an infection elsewhere in the body and settle in the bone. This is more common in children.
- Direct Contamination: This occurs when bacteria directly enter the bone due to trauma (e.g., open fracture), surgery, or a penetrating wound (e.g., a puncture wound).
- Spread from Nearby Tissue: Infection can spread from infected soft tissues near the bone, such as in a diabetic foot ulcer.
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Risk Factors: Certain factors increase the likelihood of developing osteomyelitis:
- Diabetes: Poor circulation and nerve damage increase the risk of foot ulcers and subsequent bone infection.
- Peripheral Artery Disease: Reduced blood flow compromises the body's ability to fight infection.
- Sickle Cell Disease: Impaired immune function and bone structure increases susceptibility.
- Intravenous Drug Use: Sharing needles can introduce bacteria directly into the bloodstream.
- Recent Surgery or Injury: Surgical procedures or injuries increase the risk of direct bone contamination.
- Weakened Immune System: Conditions like HIV/AIDS, cancer treatment, or immunosuppressant medications weaken the body's defenses against infection.
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Less Common Causes:
- Fungal Infections: In rare cases, fungi can cause osteomyelitis, particularly in individuals with weakened immune systems.
- Mycobacterial Infections: Tuberculosis (TB) can spread to the bones, causing osteomyelitis.
In summary, while bacterial infection is the most common cause of osteomyelitis, the route of infection and pre-existing health conditions significantly influence its development.
