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Osteomyelitis
Overview
Osteomyelitis refers to bone infection, typically from staph aureus. It develops via hematogenous spread or direct spread from surrounding tissue, often in the setting of foreign material (hardware).
It is often categorized based on the following:
- Acuity (acute vs chronic)
- Acute: days to weeks
- Chronic: months to years. A key indicator of chronic osteomyelitis is the presence of dead bone (sequestrum) and also a sinus tract through cortical bone.
- Presence/Absence of a foreign body
- Native osteomyelitis means no hardware is present
- Device-associated refers to osteomyelitis secondary to a device. This is most often an orthopedic device, such as a prosthetic joint.
- Origin (hematologic vs contiguous)
- Hematologic spread is from pathogen seeding bone in setting of bacteremia.
- Contiguous spread is from pathogen directly seeding bone from adjacent musculoskeletal tissue.
Bacterial Pathogens
Bacteria are the most common pathogen and staphylococcus aureus (MSSA and MRSA) is the most common cause of osteomyelitis (up to 75% of cases) in both adults and children.
Bacterial Pathogens
Bacteria are the most common pathogen and staphylococcus aureus (MSSA and MRSA) is the most common cause of osteomyelitis (up to 75% of cases) in both adults and children.
Less common causes include:
- Pseudomonas aeruginosa
- Staphylococcus epidermidis (coag-negative staph)
- Enterococci
- E. coli
- Salmonella
- Serratia
- Mycobacterium tuberculosis (aka Pott’s disease, tuberculous spondylitis)
- Treponema pallidum (especially syphilitic osteomyelitis of the skull)
- Streptococci
- Kingella kingae
Specific Cause/Pathogen Relationships
Overall, staphylococcus aureus is the most common cause but some specific helpful associations are as follows:
- Hardware: staph aureus (acute and chronic), staph epidermidis (chronic)
- IV drug use: staph aureus, pseudomonas, serratia
- Puncture through a shoe: pseudomonas
- Urinary involvement: E. coli
- Diabetes: group b strep
- Sickle cell anemia: salmonella
- Children: streptococci, kingella kingae
Presenting symptom
It most commonly presents with focal, gradual, dull pain at the site of infection with typical associated signs of infection: redness (rubor), heat (calor), pain (dolor), and swelling (tumor).
Site of infection
Osteomyelitis typically involves the:
- Metaphysis of long bones (eg, the femur)
- Vertebrae.
Diagnosis
Bone culture is the gold standard confirmational test for osteomyelitis but it may be unnecessary if blood cultures are positive.
ESR and CRP are helpful indicators of systemic inflammation but are nonspecific.
General Approach to Treatment
Generally, IV antibiotics are used initially, until the patient is considered stable and the area has undergone debridement. At that point, patients can potentially be transitioned to oral therapy.
The choice of antimicrobial depends on the underlying causative organism, which is post often staph aureus.
As examples:
- For MRSA (or patients with serious beta-lactam allergy) - vancomycin or daptomycin are used.
- For MSSA - cefazolin (2 g IV Q 8hrs), or nafcillin or oxacillin (2 g IV Q 4hrs), ceftriaxone (2 g IV Q 24 hrs) are typically used.