LO: Describe the main mechanisms behind haematogenous spread of pathogens and their complications
Pathogens reach bones/joints by direct inoculation (open fracture or deep surgical site infection) or haematogenous spread
Bacteremia
Transient - dental work, gut, skin breaks
Cleared quickly
Infection
Intermittent bacteremia - pneumonia, UTI
Endovascular source - persistent bacteremia, endocarditis, graft, line
Bacteria seeding
Pathogen and host factors combine at the site of seeding
Pathogen
Host
Adhesins - stick to matrix
Slow flow in capillary beds
Evade phagocytosis
Damaged endothelium
Toxins damage tissue
Foreign material - prostheses
Haematogenous spread
Organisms can be transmitted in blood clots (septic thromboembol)
Seeding by adhesion
Bacteria bind the vessel wall where flow is slow
Often one site
Seeding by embolism and impaction
Septic embolus lodges
Wedge infarct
Without a shunt, an embolus lodges in the next capillary bed it meets
flowchart TD
A[Left heart and systemic arteries]
B[Systemic capillary beds]
C[Right heart and systemic veins]
D[Pulmonary capillary beds]
A --> B
B --> |Venous return|C
C --> D
D --> |To left heart|A
Septic emboli
Right heart Lungs
Left heart Whole body
Both sides Lungs + whole body
venn-beta
title Infarcts
set A[Left heart]:10
text A1[Lungs]
set B[Right heart]:10
text A2[Body]
union A,B[Lungs + body]
Staphylococcus aureus tropism - bone and joint, spine and discs
Septic arthritis - bacterial or fungal infection inside the joint, not viral Arth - joint | algia - pain | itis - inflammation | septic - infection
Myalgia - muscle pain
Myositis - muscle inflammation My/o - muscle
Osteomyelitis - bone infection, inflammation of bone and marrow
Discitis - inflammation/infection of invertebral disc Osteo - bone | mye - marrow | disc - invertebral disc
LO: Describe the clinical features investigation and management of osteomyelitis and septic arthritis of a native joint, and why their management often differs
Main cause for both septic arthritis and osteomyelitis
Streptococci
N. gonorrhoeae
M. tuberculosis
B. burgdorferi
K. kingae
Prothesis - consider low-virulence organisms
Clinical features
Pain at the site
Tenderness
Warmth
Swelling
Reduced use/movement
Sometimes fever
Native septic arthritis
Osteomyelitis
Prosthetic joint infection
Tempo - hours to days
Acute - days to weeks
Rapid - days, virulent organism
One joint - knee
Chronic - months to years, relapsing: draining sinus
Slow - low-virulence
Active and passive movement restricted
Any bone
Timing from surgery - early, delayed, late
Children - limp
Adults - vertebrae
Spine - neurological deficit
Both septic arthritis and osteomyelitis need prolonged antibiotics
6 weeks - osteomyelitis/discitis
4 weeks - native septic arthritis
High risk of side effects
Get a relevant sample before starting antibiotics
Joint anatomy
Synovial cavity acts as a potential space
Conducive to collection formation - needs aspiration and washout for source control
Cartilage much less able to heal than bone - higher risk of irreversible damage, greater urgency
Osteomyelitis and not septic - hold off antibiotics, even for days, arrange to get important bone samples
Prosthetic joints - aspirate in theatre to reduce risk of biofilm formation
flowchart LR
A[Hot, swollen joint]
B[Septic arthritis]
C[Crystal arthritis]
D[Reactive or inflammatory]
A --> Aspirate
Aspirate --- E[ ]:::hidden
E --> B
E --> C
E --> D
classDef hidden display: none;
Aspirate - take blood cultures
Septic arthritis - pus, organisms seen on microscopy: washout and antibiotics
Crystal arthritis - gout/pseudogout: NB infection can coexist, treat for both until cultures confirmed negative