Osteomyelitis Flashcards
(46 cards)
why has the incidence of chronic osteomyelitis increased?
increased prevalence of predisposing conditions eg DM and peripheral vascular disease
What is the age distribution of osteomyelitis?
bimodal - children and adolescents and then the elderly from DM/PVD/arthroplasties
Give examples of where direct inoculation of the bone can occur
trauma
surgery
What is direct inoculation?
Where the body part is open and the bacteria enter the bone from the environment or the skin
What is contiguous spread of infection to bone?
spread of infection from adjacent soft tissues and joints
What are the risk factors for contiguous spread?
DM
chronic ulcers
vascular disease
arthroplasty
What is haematogenous seeding?
transient bacteraemia
In children which bones are most affected by haematogenous seeding and why?
the long bones as the metaphysis has a good blood supply in childhood
In adults which bones are most affected by haematogenous spread?
vertebrae and clavicle
Is haematogenous spread polymicrobial or monomicrobial
monomicrobial
What are the host factors that affect osteomyelitis formation?
behavioural factors
vascular supply
pre-existing bone/joint problem
immune deficiency
give examples of host vascular supply factors that affect development of osteomyelitis
arterial disease
DM
sickle cell disease
Which bones are affected by osteomyelitis in IVDUs?
clavicle and pelvis
Give examples of people with risk factors for bacteraemia
central lines dialysis sickle cell disease urethral catheterisation UTI
What factors in the metaphysis lead to more likely infections in the bone?
- blood flow is slower
- endothelial basement membranes are absent
- The capillaries lack or have inactive phagocytic lining cells
- High blood flow in developing bones in Children
Why are the vertebra more likely to be infected in elderly people?
With age the vertebrae become more vascular, making bacterial seeding of the vertebral endplate more likely
How do infections spread from the urethra and bladder and prostate to the vertebrae?
lumbar vertebral veins communicate with those of the pelvis by valveless anastamoses - retrograde flow through these vessels can spread the infection from the pelvis to the vertebrae
How does coagulase make a bacterium more virulent?
Coagulaseis aproteinenzyme produced by severalmicroorganisms that enables the conversion offibrinogen intofibrin.
The fibrin clot may protect the bacterium from phagocytosis and isolate it from other defenses of the host.
what factor of pathogens make them more likely to cause infection in the bone?
surface components for adhesion to matrix molecules
Which bacteria cause osteomyelitis?
S. aureus CNS G- bacilli streptococci, enterococci, anaerobes, fungi, mycobacteria eg TB
Which bacterium causes osteomyelitis in sickle cell disease?
Salmonella
What are the chronic histological changes seen with osteomyleitis?
necrotic bone seen as an island = sequestra
new bone formation = involucrum
multinucleated giant cells
neutrophils and exudates from neutrophils
lymphocytes
histiocytes
How do the sequestra and the involucrum form?
- inflammatory exudate in the marrow leads to increased intramedullary pressure
- exudate extends into the bone cortex
- rupture through the periosteum
- interruption of periosteal blood supply causes necrosis
- there are separated pieces of dead bone called sequestra
- new bone forms in these areas called involucrum
What are the symptoms of osteomylelitis?
onset over several days
dull pain at the site of OM
pain may be aggravated my movement
