Osteomyelitis Flashcards
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
What are the signs of osteomyelitis?
systemic - fever, rigors, sweats, malaise
local: acute OM: - tenderness - warmth - erythema - swelling
chronic OM:
- tenderness, warmth, erythema, swelling
- draining sinus tract
- deep ulcers that fail to heal despite treatment
- non-healing fractures
What additional signs may be seen with vertebral OM?
epidural and subdural abscesses
meningitis
paravertbral, retropharyngeal, mediastinal, subphrenic, retroperitinoeal and psoas abscesses
Septic arthritis can be a manifestation of OM, T or F?
true
How does OM spread to the joint?
infection breaks through the cortex of the bone and discharges pus into the joint
How is OM diagnosed?
blood tests :
- FBC - acute gives high WCC, but can be normal if chronic
- ESR, CRP, but can be normal
XR
MRI
bone biopsy (ie deep biopsy) and send to microbiology positive blood cultures
what are the XR changes seen with chronic osteomyelitis?
cortical erosion periosteal reaction mixed lucency Sclerosis sequestra soft tissue swelling
VIP question: How long does it take an XR to show changes in OM?
2 weeks
How long does it take to show OM on MRI?
3-5 days
What changes are seen on MRI with OM?
bone marrow oedema
and soft tissue inflammation
clinically, which radiology scan would be first line for OM and why?
XR - as XR is much faster
How many specimens at bone biopsy are needed?
2
what is seen on biopsy in OM?
inflammation
osteonecrosis
List some differential diagnoses of OM
soft tissue infection eg cellulitis and erysipelas Charcot joint avascular necrosis of bone gout aseptic fracture bursitis malignancy
How is OM treated?
debridement
hardware placement or removal
initially empirical and then targeted antibiotics
in pts with sickle cell disease, IVDUs and vascular disease need to give a prolonged duration of antibiotics
What is the most common causative organism of osteomyelitis?
S. aureus
Which antibiotics are commonly used for OM?
Flucloxacillin and fusidic acid
for 4-6 weeks, starting IV
What test is treatment guided by?
ESR and CRP
What should be done if ESR and CRP fail to respond to antibiotics?
re-imaging
What investigation is essential in OM due to TB?
biopsy
What is seen on biopsy in OM caused by TB?
caseating granulomata
What is the name given to spinal TB and how does it present?
Potts disase - presents with chronic low grade back pain
What are the differences between normal OM and TB OM?
TB OM has: slower onset Systemic symptoms Epidemiology different from pyogenic OM Blood Culture less use Biopsy essential longer treatment - 12 months instead of 4-6 weeks XR changes only seen when very advanced ie Potts disease, so MRI may be more useful
