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CNSLF Micro - Bone & Joint Infections (iv) Septic Arthritis (joint…
CNSLF Micro - Bone & Joint Infections (iv) Septic Arthritis (joint infections)
Intro
invasion of synovial membrane by microorganisms, usually with extension into the joint space
any infectious agents may cause arthritis - bacteria the most rapidly destructive
up to 25% have irreversible loss of joint function after infection - chronic effect
Risk factors
pre-existing joint disease
RA - decreased polymorph function (reduced chemotaxis)
osteoarthritis
prosthetic joints
IVDU
DM
ulcerated skin
repeated intra-articular joint injections
Pathogenesis
haematogenous seeding during transient or persistent BSI (bacteraemia) from infection elsewhere
direct introduction
joint surgery
trauma e.g. puncture wound, bites, stepping on nails
adjacent OM
rarely joint aspiration or local corticosteroid injection
arthroscopy: scope into joint (foreign body through protective layers) - risk= 1 in 1000
few organisms required to initiate infection (low inoculation dose required as site is sterile + sequestered
bacteria trigger acute inflamm synovitis
influx of acute + chronic inflamm cells
release of CKs + proteases leads to cart degradation
irreversible subchondral bone loss can be seen within a few days
Causative organisms
S aureus
40-60% of cases
don't just give flucloxacillin - need more cover
Strep
pyogenes
pneumo
B
C
G
N gonorrhoea
STI
young adults
septic arthritis = uncommon presentation
rapid joint destruction
mono or oligo arthritis
may be a/w other features of disseminated gonococcal infection
migratory polyarthritis
tenosynovitis (synovial inflamm) - wrists, ankles, small joints
skin lesions - multiple painless macules/papules on arms, legs, trunk
fever
S epidermidis
if prosthesis
low grade
indolent
biofilm
GNB
E Coli
Pseudomonas esp IVDU
Hib in children, uncommon since vaccine
anaerobes if penetrating trauma
by age...
neonates
E coli
GBS
BSIs
children under 6
S aureus
S pneumoniae
S pyogenes (GAS)
Hib
YAs
N gon
S aureus
elderly
S aureus
S pneumo
S pyogenes
GNB
Clinical features
sudden onset of pain
hot swollen joint
knee>hip>shoulder<ankle/wrist - but hip most common in children
10-20% polyarticular - 2/3 joints more likely in patients with connective tissue disease
fever
source of infection elsewhere in 50% - e.g. skin, lungs, bladder
Microbiological dx
joint aspiration to obtain synovial fluid (pre-antibiotics)
microscopy: WCC (high, predominantly neutrophils)
gram stain (ZN stain) up to 50% of microscopy +ve (25% in N gon)
culture up to 90% +ve (50% in N non)
PCR: specific for gonococcal, pneumococcal, molecular (16S rRNA)
microscopy for crystals to rule out gout, etc
blood culture, almost 50% +ve
urethral/cervial swabs if query N gon
serology if indicated
ASOT
brucella, syphilis, leptospira, borrelia burgdorferi (Lyme disease)
Non-microbiological dx
bloods
non-specific
WCC
ESR + CRP
U+E
LFTs
imaging
plain x ray not diagnostic but baseline for assessing future joint damage - may see an effusion
MRI can't distinguish infection vs inflamm early on
may require US to get fluid specimen
Tx
IV antibiotics for 2+ wks, then oral for further 2-4wks (sometimes 6) - optimum duration unknown
e.g. flucloxacillin empirically for native joint pending C+S
N gon - ceftriaxone
monitor inflamm markers
surgical drainage to remove pus - aspiration, arthroscopic washout, suction drain