Microbiology Bone and Joint infections Flashcards Preview

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Flashcards in Microbiology Bone and Joint infections Deck (39):
1

Osteomyelitis Description

A progressive infectious process resulting in inflammatory destruction, bone necrosis (sequestrum) and new bone formation (involcrum). Can be acute or chronic

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Osteomyelitis Pathogenesis requires

High innocula
Trauma
Or foreign material

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Osteomyelitis 3 Types

Haematogenous
Contiguous
Diabetic

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Osteomyelitis Haematogenous

Following bacteraemia, especially in children, metaphyseal area of long bones

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Osteomyelitis Contiguous

After trauma o surgery or overlying soft tissue infection.
May be associated with prosthesis/pins/plates

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Osteomyelitis Diabetic osteomyelitis

• A consequence of reduced vascularity, neuropathic skin changes, decreased local immunity and metabolic disturbance
• Often associated with foot ulcer (s)

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Osteomyelitis Diabetic osteomyelitis assume and treatment

Assume osteomyelitis if bone evident at the base of ulcer
Often results in amputation

8

Osteomyelitis Signs and Symptoms

May be acute → pain, swelling, overlying inflammation
Infants may have few localising signs
May be evidence of tauma, surgery
Usually chronic → may be minimal signs, often a sinus, old scars, may be acute inflammation

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Osteomyelitis X-ray findings

Periosteal thickening/elevation on Xray
Lysis and sclerosis

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Osteomyelitis Investigations

Blood cultures, FBC, CRP
Deep tissues from theatre
Sinus swabs NEVER
Wound swabs – may be heavily colonised
Imaging

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Osteomyelitis Treatment

Give antibiotics after organism found

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Osteomyelitis Pathogens

Staphylococcus aureus – most common
→ has receptors ‘adhesins’ – for bone matrix, collagen-binding adhesion (cartilage) fibronectin-binding adhesins – 9foreign material)

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Septic Arthritis → Description

Infection of joint space haematogenous or contiguous

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Septic Arthritis →Most commonly seen in

Hip or Knee
Usually mono-articular

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Septic Arthritis →Predisposition

Rheumatoid Arthritis
Joint Disease

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Septic Arthritis →Pathogenesis

Synovial membrane highly vascular
Local polymorphonuclear response
→ Release of proteolytic enzymes and bacterial toxins
→ Rapid cartilage destruction, joint effusion
→ Decreases blood supply

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Septic Arthritis → Complications

Decreased function of joint, if not treated promptly

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Septic Arthritis → Signs and Symptoms

Painful hot swollen joint +/- malaise, pyrexia
Unable to weight bear, decrease range of movement

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Septic Arthritis → Pathogens

• Staph aureus or strep
• Haemophilius influenza of <3 years – but much less common since HiB vaccine
• Neisserria gonorrhoea in young adults
• Less common → Gram-negative infection e.g. pseudomonas in IVDU
• 10% infections are polymicrobial

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Reactive Arthritis → Description

• May occur following infectious diarrhoea e.g. Salmonella, Campylobacter, Yernisina and Shigella.
• Also following Chlamydia, gonorrhoea (Reiters syndrome), hepatitis B.

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Reactive Arthritis → Investigations

• Bacteria are not cultured from the joint arthritis is an inflammatory reaction
• Serology or recent +ve stool cultures/GU swabs confirm diagnosis

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Prosthetic Joint Infections → Description

Septic arthritis in a prosthetic joint. May follow joint replacement within <3 months of replacement surgery (early infection)

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Prosthetic Joint Infections → % of joint replacement that have infections

0.5-2% of all joint replacements

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Prosthetic Joint Infections → Cause

Direct inoculation hence skin-type flora
Late – haematogenous
Biofilm produced on foreign material
Often multiple organism

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Prosthetic Joint Infections → Biofilm formation

• Many/most infection now believed to involve biofilms
• Complex communities of surface-associated cells in an extracellular matrix
• Physical protection from antibiotics
• Biofilm cells change their phenotype (may be less susceptible)

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Prosthetic Joint Infections → Diagnosis

• History, examination, ESR, CRP, X-rays, isotope, scanes, MC &S of joint aspirate
• Stain of sample

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Prosthetic Joint Infections → Treatment

1. Conservative – washout, debride, retain joint + systemic antibiotics
2. Radiacl i.e. remove prosthesis
3. Lifelong suppressive therapy if unfit for surgery 30-60% patients retain useful joint function.
4. Do nothing – if elderly comorbidities and current symptoms do not impact on quality of life

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Prosthetic Joint Infections → Treatment without removal

• Surgical drainage + 6 weeks antibiotics

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Prosthetic Joint Infections → 1 stage replacement

• Removal and replacement at the same operation (+ antibiotic loaded cement)
• 70-80% success
• May be suitable for patients unfit for 2 operations

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Prosthetic Joint Infections → Stage 2

• Removal followed by 6 weeks antibiotics (+/- cement spacer impregnated) then re-implantation
• 90-95% success rate
• May require plastic surgery, skin and muscle flaps

31

Diagnosis of Bone and Joint infection → Diagnosis method


• Blood cultures, FBC , CRP
• Pus/joint fluid/bone specimens (Before treatment)
• Multiple specimens for PJI or osteomyelitis
• Imaging – Xrays, Ultra-sound, MRI, bone scans
• (Serology if reactive arthritis, antistaphylococcal titres may be useful)
• Review previous bacteriology if recurrent problem

32

Diagnosis of Bone and Joint infection → Treatment pharma

• Combination therapy PJI
• 2-3 weeks for septic arthritis
• 4 weeks for paediatric osteomyelitis
• 6-8 + weeks for adult osteomyelitis and PJI

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Diagnosis of Bone and Joint infection → Treatment other

• Drainage of effusions/pus is essential – also provides specimen for diagnosis
• Debridement of all infected bone essential to Rx osteomyelitis (ex paediatrics)
• Removal of prosthetics joint is usually required to effectively clear infection
• NB. It is rarely necessary to start antibiotics immediately in a patients with PJI or chronic osteomyelitis – get appropriate samples for culture first

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Diagnosis of Bone and Joint infection → organisms to think of

• S aureus
• MRSA
• Streptococci
• Coliforms
• Pseudomonas –

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S aureus antibiotics

flucloxacillin _ rifampicin, fusidic acid or gentamicin

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MRSA antibiotics

vancomycin + rifampicin or fusidic acid

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Streptococci antibiotics

benzyl penicillin or cefuroxime

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Coliforms antibiotics

consider ciprofloxacin

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Pseudomonas – antibiotics

ciprofloxacin/ceftazidine + gentamicin initially – NB check sensitivities

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