Bone & Joint Infection

Question 1

Define: osteomyelitis, septic arthritis, prosthetic joint infection

Answer 1

Osteomyelitis = infection of bones
Septic arthritis = infection of a joint
Prosthetic joint infection = infection of an artificial joint replacement

Question 2

What are risk factors for bone and joint infections?

Answer 2

Direct inoculation (trauma, medical procedures, skin ulcers)
Contiguous spread from nearby SSTI infections
Haematogenous dissemination (IV devices, IV drug abuse)
Immunosuppression (DM, renal failure, sickle cell disease)

Question 3

What common microbes can cause bone and joint infections?

Answer 3

Staphylococcus Aureus (penetrates skin well)
Streptococcus Pneumoniae
B-haemolytic Streptococcus
Enteric bacteria (E.coli / salmonella)
Mycobacterium Tuberculosis (osteomyelitis in IV discs)
Staphylococcus Epidermidis when reach prosthetic joint

Question 4

What are the bone changes seen between healthy bone and chronic osteomyelitis?

Answer 4

New brittle bone
Decreased medullary cavity
Pus within cavity
Dying bone marrow

Question 5

Outline how acute osteomyelitis -> chronic osteomyelitis

Answer 5

Initial infection (small abscess) localised in cortical bone region
Abscess enlarges and infection spreads into subperiosteal space, lifting off the periosteum
Infected bone becomes necrotic from cut-off blood supply = diffuse infection with sequestrum and sinus tract

Question 6

Define the terms:
Sequestrum
Biofilm
Involucrum
Cloacae
Discharging sinuses

Answer 6

Sequestrum = infected bone becomes necrotic

Biofilm = bacteria in organic matrix on an inert surface

Involucrum = new bone formation outside sequestrum

Cloacae = pus from sequestrum escapes through involucrum through holes

Discharging sinuses = infection and pus from cloacae causes skin necrosis

Question 7

What are the key clinical features of bone/joint infection?

Answer 7

Inflammation = pain, red, swelling, warm, loss of function

Question 8

What are the clinical features of osteomyelitis and septic arthritis?

Answer 8

Osteomyelitis: fever, discharging sinuses, pathological fractures

Septic arthritis: fever, damage to articular surfaces

+ typical inflammatory signs

Question 9

How can you investigate bone or joint infections?

Answer 9

Joint aspiration: use LA to take some fluid for microscopy, culture, PCR (should be clear and colourless)
Bone biopsy in theatre under GA

Blood and skin samples
Plain X-ray show late changes (periosteal reaction 1st)
CT good for bone changes
MRI good for soft tissue changes

Question 10

What’s the management of bone and joint infections?

Answer 10

Manage sepsis
Obtain samples if possible before antibiotics
Empirical antibiotics: IV Flucloxacillin / IV Benzylpenicillin
Septic arthritis requires joint washout
Osteomyelitis requires surgery if chronic changes
Prosthetic joints require removal, joint washout, replacement