Bone and Joint Infections

Question 1

Osteomyelitis - Pathogenesis

Answer 1

• A progressive infectious process resulting in inflammatory destruction, bone necrosis and new bone formation
• Pathogenesis requires high innocula, trauma or foreign material
• 3 types:
  
  • Haematogenous
  • Contiguous
  • Diabetic
• May be acute or chronic (relapsing)

Question 2

Osteomyelitis - Haematogenous

Answer 2

• Following bacteraemia
• Escpecially in children
• Affects metaphyseal area of long bones

Question 3

Osteomyelitis - Contiguous

Answer 3

• After trauma/surgery or overlying soft-tissue infection
• Due to direct spread on infection
• Affects any ages
• Affects any bones
• May be associated with foreign bodies:
  
  • Prostheses
  • Pins
  • Plates

Question 4

Osteomyelitis - Diabetic

Answer 4

• A consequence of:
  
  • Reduced vascularity
  • Neuropathic skin changes
  • Decreased local immunity
  • Metabolic disturbance
• Often associated with foot ulcers
  
  • Assume osteomyelitis if bone is evident at the base of an ulcer
• Very hard to treat
• Progressive spread mans often results in amputation

Question 5

Osteomyelitis - Signs and Symptoms

Answer 5

• Possible acute symptoms
  
  • Pain
  • Swelling
  • Overlying inflammation
• Infants may have few localising signs
• May be evidence of surgery or trauma
• Possible chronic signs
  
  • May be minimal
  • Often a sinus (communiation with skin)
  • Old scars
  • May be acutely inflammed
• On X-ray
  
  • Periosteal thickening/elevation
  • Lysis and sclerosis

Question 6

Osteomyelitis - Investigations

Answer 6

• Investigate
  
  • Blood cultures
  • FBC
  • CRP
  • Deep tissue swabs from theatres
  • Wound swabs? - may be heavily colonised with skin flora
  • Sinus swabs - NO due to contamination with skin flora
  • Imaging
• Don’t initate antibiotics until necessary samples are taken

Question 7

Osteomyelitis - Pathogens

Answer 7

• Most common is Staphlococcus aureus
  
  • **Adhesin **receptors bind
    
    • Bone matrix
    • Cartilage - collagen-binding
    • Foreign material - fibronectin-binding
• Infants
  
  • Group B Streptococci
  • Staphlococcus aureus
  • E. Coli
• ​Children 1-6 years
  
  • Staphlococcus aureus
  • Streptococcus pyogenes
  • H.influenzae
• ​Adults
  
  • Staphlococcus aureus
  • Staphlococcus epidermis
  • Pseudomonas aeruginosa
  • Gram negatives e.g. E.coli

Question 8

Septic Arthritis

Answer 8

• Infection of joint space
  
  • Haematogenous
  • Contiguous
• Most commonly hip or knee
• Usually monoarticular
• Predisposed to if existing:
  
  • Rhematoid arthritis
  • Joint disease

Question 9

Septic Arthritis - Pathogenesis

Answer 9

• Synovial membrane is highly vascular
• Local polymorphonuclear response –>
  
  • Release of proteolytic enzymes and bacterial toxins
  • Rapid cartilage destruction + joint effusion
  • Drecreased blood supply due to compression of vasculature

Question 10

Septic Arthritis - Signs and Symptoms

Question 11

Septic Arthritis - Pathogens

Answer 11

• Most commonly *Staphylococcus aureus *or Streptococcus species
• *Haemophilus influenzae *if much less common since HiB vaccine
• *Neisseria gonorrhoea *in young adults - !
• Less commonly Gram-negative infection e.g. Pseudomonas in IVDU
• 10% of infections are polymicrobial

Question 12

Reactive Arthritis

Answer 12

• May occur following infectious diarrhoea:
  
  • Salmonella
  • Campylobacter
  • Yersinia
  • Shigella
• ​Following STIs = ‘Reiter’s syndrome’ (+ conjunctivitis, arthritis +/- rash)
  
  • Chlamydia
  • Gonorrhoea
• ​Also may be due to Hepatitis B
• Bacteria will not be cultured from the joint as arthritis is an inflammatory reaction to infection elsewhere
• Investigate to confirm diagnosis with:
  
  • Serology
  • Stool cultures
  • GU swabs

Question 13

Prosthetic Joint Infection

Answer 13

• Septic arthritis in a prosthetic joint
• May follow joint replacement
  
  • • Months-years after surgery = late infection
• Follows 0.5-2% of all joint replacements
• Symptoms may be mild - joint pain/discomfort

Question 14

Prosthetic Joint Infection - Pathogenesis

Answer 14

• Early infection usually due to direct inoculation - skin type flora
• Late infection usually haematogenous
• Often multiple organisms
• Leads to a biofilm on the foreign material
  
  • Thought to be involved in most infections now
  • Compled communities of surface-associated cells in an extracellular matrix
  • Provided physical protection against antibiotics
  • Cells may change phenotype making them less susceptible to treatment
  • Sometimes bacteria stop dividing and become dormant - resistant to abx targeting division

Question 15

Prosthetic Joint Infection - Diagnosis

Answer 15

• Often difficult
• Hx & examination
  
  • Chronic infection fewer signs than acute
• ESR
• CRP
• Isotope scans
• MC&S of joint aspirate
  
  • Bacteriological diagnosis important
  • Gram stain of joint fluid has poor sensitivity - culture better

Question 16

Prosthetic Joint Infection - Conservative Treatment

Answer 16

• Conservative
  
  • Joint retained
  • Drainage, washout and debridement of joint
  • 6 weeks of antibiotics
  • Risk of missing adherent bacteria to cement/prosthesis if only rely on aspiration for diagnosis
  • Success rate approximately 20% - better in:
    
    • Early post-op cases when treatment is intiated promptly
      
      • >80% failure rate if debrided >2 days after symptoms present
    • Avirulent organisms i.e. not Staphylococcus aureus
• Lifelong suppresive therapy if unfit for surgery
  
  • 30-60% of patients retain useful joint function
• Do nothing if elderly or comorbidites and symptoms do not impact on quality of life

Question 17

Prosthetic Joint Infection - Radical Treatment

Answer 17

• Involves removal of prosthesis
  
  • 1 stage replacement
    
    • Removal and replacement in same operation
      
      • Uses antibiotic loaded cement
    • 70-80% success
    • May be suitable for patients unfit for 2 operations
  • 2 stage replacement
    
    • Removal followed by 6 weeks abx (+/- cement spacer impregnated with abx)
      
      • Then re-implantation
    • 90-95% success rate
    • May require plastic sugery and skin/muscle flaps

Question 18

Treatment - Bone/Joint Infections

Answer 18

• Seek advice dependent on culture results
• Combination theapy recommended for PJI and often osteomyelitis
• Abx course:
  
  • 2-3 weeks for septic arthritis
  • 4 weeks for paediatric osteomyelitis
  • 6-8+ weeks for adult osteomyelitis and PJI - may need to continue for:
    
    • Months if prosthesis remains in place
    • Years if infection is persistant and can’t be cured
• Drainage of effusion/pus is essential
  
  • Also povides specimen for diagnosis
• Debridedment of all infected bone material essential in osteomyelitis (except paediatric)
• Removal of prosthetic joint usually required to clear infection
• NB - rarely necessary to start antibiotics immediately in patients with PJI or chronic osteomyelitis - get appropriate samples for cultures first

Question 19

Treatment - Bone/Joint Infections: Antibiotics

Answer 19

• Sensitivities:
  
  • *Staphlococcus aureus - **flucloxacillin + rifampicin *or fusidic acid or gentamycin
  • MRSA - vancomycin + rifampicin or fusidic acid
  • Streptococci - benzypenicillin **or **cefuroxime
  • *Coliforms - *consider ciprofloxacin
  • *Pseudomonas - ciprofloxacin/ceftazidime + gentamycin *initially -** ! **check sensitivities
• IV vs oral
  
  • Possible to use oral antibiotics for switch therapy
  • Some e.g. clindamycin or ciprofloxacin can be used as part of combination therapy for long-term treatment
  • **! **- advice important
    
    • Some oral abx are poorly absorbed from gut e.g. penicillin
    • Some penetrate bone poorly e.g. some cephalosporins

Question 20

Reducing Contamination of Operative Site

Answer 20

• Main sources of contamination
  
  • Patient skin flora
  • Hands of surgical team
  • Pre-existing infection
  • Airborne from:
    
    • Skin
    • Mucous membranes
    • Clothing of patient/surgical team