Pathology II Flashcards
What is osteomyelitis?
Inflammation of bone
- Generally due to infection, mostly by bacteria
- Progressive infection
- Inflammatory destruction of bone, followed by new bone formation
What are risk factors for osteomyelitis?
Not very common in healthy individuals b/c bone is resistant to infection
Risk factors:
Trauma
Diabetes
Decubitus Ulcers
Intravenous Drug Use
Surgery
How does infection get into the bone?
- Spread from a contiguous focus of infection
- Direct innoculation (trauma, surgery)
- Hematogenously
(long bones and vertebral bodies)
(long bones common in children)
How does Hematogenous infection occur?
- Infection enters through nutrient artery and into metaphysis
- Bone destruction and absess formation at metaphysis
- If young child, can progress to epiphysis and then to joint
- In all patients, over time extends through bone, eventually involving compact bone and raises periosteum from cortex, leading to new bone formation
- Inflammatory response results in sequestrum
What is sequestrum?
Inflammatory response to osteomyelitis results in:
- Increasee pressure within bone
- Leading to thrombosis of branches of nutrient artery and compression of capillaries within Haversian canals
- Resulting in necrosed bone within bone (sequestrum)
What is the clinical presentation of osteomyelitis?
Chills, fever, sweats
lethargy, malaise
point tenderness
swelling of tissues over bone
redness of tissues over bone
draining sinus
What are microbiological causes of osteomyelitis?
STAPHYLOCOCCUS!
Coagulase-negative Staphylococci
Cat/Dog bite: Pasteurella
Human bite: Eikenella
** IV Drug use:** Pseudomonas
Why is staphylococcus so prevelant in osteomyelitis?
S. aureus has Collagen Adhesin (biofilm)
- Inhibits clearance by immune system
- Inhibits penetration of antibiotics
How is biofilm produced?
Quorum sensing
- Bacterial presence signal is synthesized
- Signal diffuses through environment
- Signal binds to neighboring bacterial receptor
- Recetpor binds to promotor
- Gene Expression ==> Bacterial attachment, motility, biofilm formation, oxidative stress response, vitamin synthesis
What test are generally used to diagnose osteomyelitis?
Radiological Tests:
X-ray (usually need follow up xrays)
MRI (most sensitive and specific)
Nuclear studies
CT scan (better than x-ray)
Probe to bone:
contact with bone through cubitous ulcer, generally +
Blood culture:
Sometimes…
Most Definitive: Bone biopsy
What are general principles for treating osteomyelitis?
Acute disease = No bone necrosis, no abscess
Abx alone usually sufficient
Vertebral osteo and terminal digits ==> Abx alone
All others ==> surgical debridement + abx
Antibodies are generally IV for 4-6 weeks
Surgery includes debridement and removal of any hardware in affected area, management of dead space, improvement of blood flow if necessary
How do joints get infected?
Primarily by hematogenous seeding
Less common: penetrating trauma (bite, injury) complication of joint injection w/corticosteroids
What are risk factors for synovial joint infection?
- Other joint diseases:
RA
Osteoarthritis
lupus
gout
pseudogout
prior trauma or injection - Prosthetic joint
- IV drug use
- Alcoholism
- Diabetes
- Cutaneous ulcers and other skin conditions
- Immune suppression
What is the clinical presentation of Synovial joint infection?
Chills and fever
Swollen, red, warm, painful joint
decreased joint mobility
What are common microbiological causes of joint infections?
Staphylococcus aureus!
Lyme disease
Gonococcal infection
