Prosthetic joint infection

Question 1

What are is the epidemiology of TKR and THR joint infections?

Answer 1

• 1-2% following primary TKR
• 6% following revision TKR
• 0.3%-1.3% following primary THR
• 3% following revision THR

Question 2

What are the risk factors for Prosthetic joint infections?

Answer 2

• Immunosupressants drugs
  
  • anti- TNF agents
  • antimetabolites- Methotrexate/leflunomide
  • Corticosteriods
• Immunosuppressant conditions- dysplasia/neoplasia
• Perioperative surgical site infection
• poor wound healing
• RA
• Psorasis
• Diabetes
• Smoking
• Obesity

Question 3

What are the organisms involved in Prosthetic joint infections?

Answer 3

• most common
• Staphylococcus aureus
• Staphylococcus epidemidis
• Coagulase negative staphylococcus ( chronic infection)
• Most common fungal
  
  • Candida species

Question 4

How do you prevent Prosthetic joint infections?

Answer 4

• Antibiotic administration within 30 mins of incision and cotinued for 24 hrs after surgery- most effective
• Vertical laminar flow systems in operating rooms
• antibiotics prior dental work is cost -effcetive for 2 years following major joint replacement

Question 5

What is the classification of Prosthetic joint infections?

Answer 5

• Acute
  
  • infection within 3 weeks of Joint replacement
  • usually confined to joint space
  • Staph aureus/ B haemolytic strep/Gram- neg
• Chronic
  
  • ​infection > 3 weeks
  • Biofilm created by all bacterial forms on implant by 4 weeks
    
    • ​15% cells and 85% polysacchardie layer ( glycocalyx)
    • Glycocalyx allows biofilm to adhere to prothesis and seal off infection and protect from host immune system
    • = bacteria to become 1000 x more resistant
    • infection invaded prosthetic- bone interface
    • coag neg staphylococcus most common
• Haematogenous seeding
  
  • infection in a longstanding infection-free joint secondary to another infection ( dental work/gallbladder)

Question 6

What is the presentation of Prosthetic joint infections?

Answer 6

• Pain on site of arthroplasty assoc with infection >90% pts
• acute onset swelling, erytherma, warmth and tenderness
• chronic- function and pain worsens over time

O/E

• sinus tract joint is a definite infection

Question 7

What is seen on imaging of Prosthetic joint infections?

Answer 7

• Xray
  
  • Periosteal reaction
  • scattered patches of osteolysis
  • generalised bone rebsorption without implant wear
• Bone scan
  
  • Tc99m detects inflammation, In-111 ( indium) detects leucocytes
  • 99% sensitive, 30-40% specific
• PET- positron emission tomography
  
  • identifies areas of high metabolic activity using fluorinated glucose
  • sensitive 98%, specific 98%

Question 8

What lab studies are helpful in Prosthetic joint infections?

Answer 8

• WBC
  
  • >10,700 cells/ul <4 wks from surgery
  • >1760 cells /ul >4 wks from surgery
• ESR/CRP
  
  • CRP takes 21 days to return to normal post surgery
  • ESR takes 90 days to return to normal post surgery
  • If remain elevated or increase- concern
• IL-6
  
  • greatest correlation with Prosthetic joint infections
• Joint aspiration
  
  • Synovial WBC >1,110 cells/ml
  • PMN >64%
• ​Microbiology
  
  • ​definitive dx made if same organism found on 3-5 periprosthetic specimens obtained at surgery

Question 9

What is the tx of Prosthetic joint infections?

Answer 9

• Non operative tx
  
  • Suppressive antibiotic therapy
    
    • pts unfit for surgery/refyse surgery
    • Goal is to prevent systemic infection
    • 10-25% success rate with eradication
    • 8%-21% complx rate
• ​​Operative
  
  1. ​PE exchange, debridement , irrigation with component retention, iv ab for 4-6 wks
     
     • acute infections <4 wks, early haematogenous infection <4 wks
     • 80-90% successful outcome
  2. One stage revision replacement arthroplasty
     
     • ​low virulence organism and know sensitivities
     • no bone graft/healthy pt
     • antibiotic loaded cement
     • adv
       
       • lower cost and convience of single procedure
       • early mobility
     • Dis
       
       • higher risk of continued infection from residual organisms
     • variable success 75-100%​​​​​
  3. ​Two stage replacement
     
     • ​​gold standard for infected joints >4 /52
     • medically fit for multiple operations
     • Requires adequate bone stock
     • prosthesis removal, antibitoic spacer, Iv antibiotics 4-6 wks and delayed reconstruction
     • delayed implanation>6 wks success 70-90% cf 2 weeks 35% success
  4. ​Resection Arthroplasty
     
     • ​​elderly,non ambulatory, recurrent infections, failure of reimplanation
     • total knee success 50-89%
     • Total hip success 60-100%
     • Dis: short limb, poor function, pt dissatisfaction
  5. Arhrodesis
     
     • if remimplantaton not feasible
     • outcomes 71-95% success rate
  6. Amputation
     
     • AKA transfemoral amputation for infected TKR

Question 10

What are the adv and dis of cement spacers?

Answer 10

• Adv
  
  • reduce joint dead space
  • provide stability
  • deliver high dose antibiotics
• Disc
  
  • potential local or systemic allergic reaction
  • increase chance of developing antibiotic resistant organisms
  • only heat stable antibtiotics can be added to cement

Question 11

What type and amount of antibiotic can be added to cement for a spacer?

Answer 11

• each 40g bag of cement should have 3g of vancomycin and 4g of Tobramycin added
• Gentamycin can be subsituted for tobramycin
• elution of antibiotics depends on cement porosity, surface area ( beads increase area) and antibiotic concentration
• must use heat stabilised antibiotics- vanc, gent, tobramycin

Question 12

What antibiotics should be used in Prosthetic joint infections?

Answer 12

• 1st generation cephalosporin
• vancomycin
  
  • if pencillin allergic
  • priod hx exposure to mrsa
  • unidentified organism
• Tailor regimen based on microorganism & susceptibility testing