Bone and Joint Infection

Question 1

What is osteomyelitis

Answer 1

Osteomyelitis = infection of bones

Question 2

What is septic arthritis?

Answer 2

infection of joints

Question 3

What is osteomyelitis

Answer 3

Osteomyelitis = infection of bones 25% of open fractures lead to osteomyelitis and

Question 4

What is prosthetic joint infection?

Answer 4

infection of an artificial joint replacement 1% of joint replacements lead to prosthetic joint infections

Question 5

Name some Microbes which cause bone and joint infections?

Answer 5

Staphylococcus aureus (including MRSA) Streptococci (β-haemolytic Streptococci species & Strep. pneumoniae) Enteric bacteria (eg. E. coli & Salmonella species) Coagulase-negative Staphylococci (eg. Staph. epidermidis) Mycobacterium tuberculosis (& other Mycobacteria too) Others (Lyme borreliosis, gonorrhoea, brucellosis, fungi, parasites)

Question 6

Name some risk factors for bone and joint disease

Answer 6

Direct inoculation eg. trauma, medical procedures, skin ulcers Contiguous spread eg. nearby skin or soft tissue infection (SSTI) Haematogenous dissemination eg. IV devices, IV drug abuse Immunosuppression eg. diabetes mellitus, renal failure, sickle cell disease

Question 7

What microbial factors affect how a bacteria causes infection?

Answer 7

Access : can they reach a suitable site for adherence & invasion ? Adherence : can they stick or bind to a suitable site for invasion ? Invasion : can they penetrate the barriers to infection ? Multiplication : can they replicate to cause infection ? Evasion : can they evade the host immune system ? Resistance : can they resist anti-microbial treatments ? Damage : do they damage host cells (directly or indirectly) ? Transmission : can they be released to infect other hosts ?

Question 8

MICROBIAL FACTORS SLIDE 13

Question 9

HOST RESPONSE SLIDE 14

Question 10

HOST RESPONSE SLIDE 15

Question 11

If acute infection progresses to become chronic infected bone can become necrotic, what changes in the bone would be seen?

Answer 11

A sequestrum is a piece of dead bone that has become separated during the process of necrosis from normal or sound bone. It is a complication (sequela) of osteomyelitis.

Question 12

In chronic infection, bacteria in an organic matrix can collect on an inert surface, this is called?

Answer 12

Biofilm

Question 13

In chronic infection when new bone forms outside sequestrum this is called…

Answer 13

Involucrum

Question 14

In chronic infection when pus from sequestrum escapes through involucrum via holes this is called..

Answer 14

Cloacae

Question 15

In chronic infection, infection & pus from cloacae causes skin necrosis, this is called…

Answer 15

discharging sinuses

Question 16

Explain what would be seen in bone with an acute infection that has progressed to become a chronic infection

Answer 16

Infected bone becomes necrotic = sequestrum

Bacteria in an organic matrix on an inert surface = biofilm

New bone formation outside sequestrum = involucrum

Pus from sequestrum escapes through involucrum via holes = cloacae

Infection & pus from cloacae causes skin necrosis = discharging sinuses

(Biofilms also form on prosthetic joints & assist infection)

Question 17

HOST RESPONSE CHRONIC OSTEOMYELITIS SLIDE 17

Question 18

BIOFILMS SLIDE 18

Question 19

What are the clinical features of inflammation caused by infection?

Answer 19

pain,

swelling,

redness,

warmth,

loss of function

Question 20

What are the clinical features of osteomyelitis?

Answer 20

• Pain
• swelling
• redness
• warmth
• loss of function
• fever
• pathological fractures
• discharging sinuses

Question 21

Wha are the clinical features of septic arthritis?

Answer 21

• Pain
• swelling
• redness
• warmth
• loss of function
• fever
• damage to articular surfaces

Question 22

What investigations would you request if you were suspecting a bone or joint infection?

Answer 22

Full blood count (FBC) & inflammatory markers (eg. CRP)

Other blood tests to look for evidence of severe sepsis

Blood cultures (x2) & skin/ulcer swabs (inc. MRSA)

Question 23

What imaging studies would you request if you were suspecting bone or joint infection?

Answer 23

Plain radiographs : show late changes well, but not early changes (periosteal reaction is earliest sign visible)

CT scans : show bone changes well, but not as good for soft tissues changes

MR scans : show soft tissue changes well, but not as good for bone changes

Question 24

Outline treatment steps for bone and joint infection

Answer 24

Manage sepsis

Obtain samples (if possible) before starting antibiotics

Empirical antibiotics = IV flucloxacillin & IV benzylpenicillin

Targeted antibiotics = dependent on culture & sensitivities

Duration of antibiotics = 2-6 weeks IV then 4-6 weeks PO

Septic arthritis requires a joint “washout” (in theatre)

Osteomyelitis requires surgery if chronic changes have developed

Prosthetic joint infections require removal & then replacement

(with antibiotics continued in between operations)

Question 25

How can we best prevent bone and joint infections in clinical practice?

Answer 25

Prompt diagnosis & treatment of predisposing conditions

Strictest possible aseptic conditions for joint replacements

Antibiotics embedded into cement used for prosthetic joints