Osteomyelitis is the inflammation of bone secondary to infection.
It can be classified by duration (acute, subacute, or chronic), route of infection (haemtogenous or exogenous), or byt the host response (pyogenic or granulomatous)
Route of infection
Haematogenous
This is when a bacteraemia ends up in the bone and established itself. It is most common in children due to the vascular stasis at the growth plates ( question ) and also makes up 20% of adult cases. This is usually monomicrobial
Exogenous
This can occur from direct infection from trauma (open or compound fracture), or surgery (both of which are more common in adolescents and younger people), or Contiguous spread from a local infection (more common in older adults)
Infective species (aetiology)
The common causative for each route of infection are as listed.
Haematogenous
Remember this is often monomicrobial
| Age | Pathogen |
|---|---|
| Neonates (premature) | S. aureus, S. agalactiae, E. coli |
| Children/adolescents | S. aureus, S. pyogenes, S. pneumoniae, E.coli |
| Adults | S. aureus, streps/enterococci, Gram-negatives |
Exogenous
Often polymicrobial
- S. aureus
- Streps/enterococci
- Gram negatives
- Obligate anaerobes
Staphylococcus aureus
This organism is responsible for 90% of child infections and 30-50% of infections in adults.
Risk factors
The Risk factors for this disease are the common ones: immunosuppression, age, peripheral vascular disease, injecting drug user, and some others like chronic joint disease and recent bone surgery.
Clinical things to know
In children
Osteomyelitis often affects the metaphysis of long bones, with severe pain, oedema, and erythema being observed. Pseudoparalysis, fever malaise nausea and vomiting can also occur. In infants the symptoms are less dramatic.
Adults
haematogenous spread has loss acute onset, with spine and pelvis being common past 45 yrs and can just present as complaints of backache. A common presentation for is diabetics with foot ulcers and osteomyelitis resulting from that.
Complications of disease
There are severe complications to this disease with some being
- Septic arthritis
- Sepsis
- metastatic infection
- progression to chronic or recurrent osteomyelitis
- Altered bone growth (esp in children, could leave with lifelong disability)
- And lead to pathological fractures
Pathogenesis
I wont explain this stepwise like i would normally but list some of the stuff all happening at once.
The inflammation from the infection leads to swelling but if it occur in the bone this will lead to increased pressure, not allowing blood intot he bond (vascualr congestion). This in turn leads to ischaemia and necrosis, and osteolysis. This necrosis leaves dead bone, which can serve as a nexus of further infection. This is called the sequestrum (like sequester away) In healing the seqestrum is covered by new bone (kinda like how vines can grow over an old dead tree (look up norther rata)), This is called the involucrum. This can encapsule the sequetrum leaving a poitn of further infection (recurrent and chronic osteomyelitis). Also suppuration can occur witht he pus produced evenutally being drained with a sinus formation over the chronic infection.
Diagnosis
Aspirate pus form the bone before antimicrobials. Gram stain it and base empiric therapy of findings. also culture the pus but 25% of cases are negative. You can also blood cultures to check for haematogenous osteomyelitis. Obviously in more progresses cases Xrays will show significant bone changes. This requries >50% of bone to be lost though. A CT scan can show more difficult to bones and an MRI is useful for early diagnosises You could do a PET scan check for early infections.
Treatment
Pharmacological
Use IV empiric broad spectrum drugs or combinations of drugs. For S. aureus, streptococci, Pseudomonas, or E. coli use:
- Flucloxacillin, vancomysin (S. aureus/MRSA/S. epidermidis)
- Penicillin (Streps)
- Cephalosporins/fluoroquinolones (E. coli)
- ß-lactams + ß lactamase inhibitor/ fluoroquineolone/carbapenem (Pseudomonas) When your cultures and stains get back use narrow spectrum drugs. Additionionally the antimicrobial therapy will need to be prolonged 4-6 wks IV and 2-4 wks Oral
Surgical
Some surgical options that may be required are: Debridement (surgical cleaning) to clear dead bone and pus and Amputation for diabetics sadly.
There is more content on subacute and chronic osteomyelitis but i ceebs rn finishthis