Bone and Joint Infections Flashcards by Srishti D

How can an asymptomatic bacteraemia happen?

Pull out tooth
Pass stool
Usually happens when you do nothing - immune system clears it

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What is the most common source of bone and joint infection in children?

Haematogenous

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What can cause bone and joint infections through direct inoculation?

Trauma
- Fractures
- Puncture wounds
Surgery
- Pins

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What can cause bone and joint infects through local invasion?

Pressure ulcer
Periodontal disease
Sinus disease

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How does haematogenous osteomyelitis occur?

In metaphysis have looped capillaries and venous sinusoids
Blood goes very slowly through these
Bacteria seed metaphyseal-epiphyseal junction
Protected from immune response
Bacteria can establish and infect bone
Pressure from pus further limits blood supply
Established infection enlarges
Limited by growth plate
Infection therefore spreads into periosteum and supperiosteal space

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Why is bacteria seeded in the metaphyseal-epiphyseal junction protected from the immune response?

Poorly developed reticular endothelium system
Poor penetration of WBCs
Diminished immune mediators

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What happens once infection spreads into the periosteum and subperiosteal space?

Lifts periosteum

Invades shaft

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What is the most likely source of osteomyelitis in adults?

Direct inoculation

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What is the definition of an infant?

Less than 1 year old

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Why are infants’ joints particularly at risk of infection?

Growth plate not as good a barrier between bone and joint
Vessels cross growth plate
Infection can easily spread from bone to joint

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How can septic arthritis occur?

Haematogenous contamination: blood > joint space
Direct contamination
- Trauma
- Surgery
Contiguous contamination from bone

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What is the most common cause of bone and joint infections?

Staphylococcus aureus

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What is the second most common cause of bone and joint infections?

Streptococcus pyogenes

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To which bacteria are you more susceptible to after a chicken pox infection, in terms of bone and joint infections?

Streptococcus pyogenes

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Which bacteria are newborns and infants susceptible to from the birth canal, which can cause bone and joint infections?

Group B Streptococcus
Haemophilus influenzae type b
Other Gram negative bacteria
- Enterobacter
- Pseudomonas
- E coli

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Which bacteria are people after surgery susceptible to, that can cause bone and joint infections?

Coagulase negative staphylococci

Often from skin
Eg: Staphylococcus epidermidis

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Which bacteria are people susceptible to if they’re in developing countries, in terms of bone and joint infections?

Haemophilus influenzae type b

Mycobacterium tuberculosis

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Which Gram negative bacteria are slightly more common causes of bone and joint infections in children?

Kingella kingae

Salmonella

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Which bacteria can cause bone and joint infections via a sneaker penetration injury?

Pseudomonas

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What host factors make you more susceptible to a bone and joint infection?

Genetic
Young age
Recent respiratory infection
Neuroanatomical defects
Immunodeficiency

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What proportion of people carry S aureus as part of their normal skin flora?

30%

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What S aureus strain is most likely to cause bacteraemia?

Those colonised in their nasopharynx

What proportion of bone and joint infections occur in those under the age of 5?

50%

What is the ratio of bone and joint infections in boys:girls?

2:1

What increases your risk of contracting a bone and joint infection?

Aboriginal and Maori Sickle cell disease Immunocompromise Neonates

What are the clinical features of bone and joint infections?

``` Fever Pain and localised tenderness Joint/bone may feel warm Erythema Oedema History of preceding trauma in 1/3 of cases ```

What can cause delayed presentation of bone and joint infections?

``` Subperiosteal collection Signs include - Local erythema - Tenderness - Swelling ```

What are the most common bones in which infections occur?

Long bones - Humerus - Femur - Tibia

Why are infections more common in tubular rather than flat bones?

Grow faster

What are the most common bones in which infections occur in babies?

Humerus Femur Tibia Hands and feet

How can vertebral osteomyelitis present?

Delayed presentation Occurs in older children Dull, constant back pain for long time

How does a delayed diagnosis of pelvic osteomyelitis present?

Vague pain in buttocks and groin

Why are infections difficult to diagnose in neonates?

Hard to work out where they are

What are the differential diagnoses for osteomyelitis?

Septic arthritis - Often co-existent Malignancy Cellulitis

What can indicate a malignancy rather than osteomyelitis?

FBE X-ray Absence of fever and inflammatory markers Delayed response to drugs

What do blood tests show in osteomyelitis?

White cell count can be normal > FBE and film essential | CRP/ESR increased >90%

What is the CRP and ESR profile in osteomyelitis?

CRP rises rapidly over 1st 24 hours If infection treated, decreases over 1-2 weeks ESR goes up much slower over 48 hours Comes down over prolonged period of weeks

How are x-rays used in the diagnosis of bone and joint infections?

Only useful in osteomyelitis Often normal May see swelling in 1st few days Sometimes done in children to exclude non-accidental injury

How are bone scans used in the diagnosis of bone and joint infections?

Increased uptake of isotope in area of infection | Highly sensitive and specific

What cultures are done in bone and joint infections?

Blood - Often bacteraemia cleared but bone and joint infection established Bone Pus aspirated from bone

When is a biopsy done in bone and joint infections?

``` Delayed presentation Predisposing condition Unusual radiographic findings High likelihood of MRSA Suspected complication; eg: abscess Suspected alternative diagnosis; eg: malignancy Delayed response to antibiotics ```

When is flucloxacillin used to treat bone and joint infections?

Majority of S aureus susceptible to it | Kills all Gram positive causes

How is flucloxacillin administered?

High doses | IV

Which antibiotic is more commonly used in adults instead of flucloxacillin, and why?

Dicloxacillin, because less likely to cause liver toxicity

What are the treatment options if MRSA is present?

Vancomycin | Combination of rifampicin and fusidic acid

What is the treatment if - Neonatal? - Gram negative bacteria - Unimmunised for H influenzae?

Flucloxacillin and cefotaxime

What antibiotic is added to create synergy for difficult cases of bone and joint infections?

Fusidic acid | Rifampicin

What antibiotics are used to treat Pseudomonas bone and joint infections?

Timentin and gentamicin

For how long are bone and joint infections treated for?

3-5 days IV | Complete 3 week course with oral high dose antibiotics

What route of administration is used in neonatal cases of bone and joint infections?

IV for full duration

When might longer treatment for bone and joint infections be needed?

Unusual sites

What is chronic osteomyelitis often associated with?

Suboptimal initial treatment

What are the treatment options for chronic osteomyelitis?

Surgical debridement and long-term antibiotics - IV 2 weeks - Oral 3-6 months or more