Bone and joint infections Flashcards
Describe the classification of osteomyeltitis?
Haematogenous: could have come from anywhere in body and entered blood > bone
Non haematogenous - direct inoculation: bacteria from outside world get direct entry (trauma, surgery)
Non haematogenous - local invasion: e.g. pressure ulcer
From where in the blood do bacteria usually enter the bone?
Looped capillaries and venous sinusoids
Slow flow through here > lodge
Describe the pathogenesis of osteomyelitis?
1) Slow flow through looped capillaries and venous sinusoids
2) Bacteria seed metaphyseal-epiphyseal junction
3) Abscess forms > protected from immune response
4) pressure from pus further limits blood supply
5) Infection spreads to subperiosteal space > lifts periosteum, invades shaft
How can infection invade the epiphysis and joint in children?
Vessels that cross growth plate are still present in children, not in adults
Describe the situations in which septic arthritis may develop?
Direct contamination (surgery, trauma)
Haematogenous contamination
Contiguous contamination (bone > joint) in children
How are the pathogenic agents of osteomyelitis categorised?
Gram positive
Gram negative
Other (TB, fungi, parasites)
What are the most common Gram positive agents of osteomyelitis?
Staph aureus
Strep pyogenes/Group A strep
(Strep pneumoniae, Group B strep, coagulase negative staph)
What are the most common Gram negative agents of osteomyelitis?
Kingella kingae
Salmonella
(Haemophilus influenzae type B)
What is the single most common agent of bone and joint infection?
Why?
Staph aureus
Possesses virulence factors
Colonises our skin commonly
What are the most common agents of bone and joint infection after surgery?
Gram negative staph
What are the most common agents of bone and joint infection in newborns/infants?
Group B strep
Hib
Other Gram negative organisms (Enterobacter, Pseudomonas, E.coli)
What are the most common agents of bone and joint infection in people with chicken pox?
Strep pyogenes/Group A strep
What are the most common agents of bone and joint infection in sneaker penetration injuries?
Pseudomonas
What are the most common agents of bone and joint infection in developing countries?
Hib
TB
Which populations are most at risk of developing osteomyelitis?
Under 5 yo (50% of infections)
Boys (2:1)
Aboriginal and Maori children
Sickle cell disease
Immunocompromised
Neonates
Describe the clinical features of bone and joint infection?
Pain
Pseudoparalysis
Fever
Malaise
Tenderness
Swelling
Heat
In which bones does osteomyelitis most commonly occur?
Long bones
Femur > tibia > humerus
What are the important differential diagnoses for osteomyelitis?
Septic arthritis (often coexistent in children)
Malignancy
Cellulitis
Describe the diagnosis of osteomyelitis?
Clinical signs
X-ray, bone scan or MRI evidence
Positive blood or bone culture
Pus aspirated from bone
Describe the CRP and ESR levels in osteomyelitis?
Elevated >90%
CRP rises very quickly in first 24 hours
ESR rises and falls more slowly
Describe the use of imaging to diagnose osteomyelitis?
PLAIN FILM
Not very good early on
Helpful for excluding fractures and malignancy
After 3 days, may see some swelling
After 2 weeks, will see periosteal lift
BONE SCAN
More sensitive and accurate early on
MRI
Very accurate, very high sensitivity
Describe the treatment of osteomyelitis?
Flucloxacillin: for all Gram positive causes except coagulase negative staph
If neonatal (Gram negatives) or unimmunised (Hib): flucloxacillin and cefotaxime
Difficult cases: rifampicin
3-5 days IV treatment, followed by 3 weeks oral treatment for uncomplicated patient
In which situtation does osteomyelitis develop?
Suboptimal treatment of initial osteomyelitis
