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- Staphylococcus aureus is most common
- Polymicrobial infections are second most common
- Coagulase-negative Staphylococcus (CoNS) is also common
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- I will investigate with biochemical, radiological, and aspiration tests guided by the MSIS criteria
- Bloods (2) - WCC, CRP, ESR
- XR - Look for loosening and lytic lesions
- Aspirate (4) - Alpha defensin, PMN %, cell count
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- Radionuclide studies
- Technetium 99m bone scan combined with WBC scan is the most specific scanning method
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- 2 + (2+4) + 4
- The MSIS (Musculoskeletal Infection Society) criteria for diagnosing periprosthetic joint infection (PJI) involve a combination of major and minor criteria, with major criteria including two positive cultures of the same organism or a sinus tract with evidence of joint communication. A definitive diagnosis of PJI requires meeting the major criteria or a combination of preoperative and intraoperative minor criteria totaling six points or more. Minor criteria include elevated inflammatory markers like ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein), elevated synovial fluid white blood cell (WBC) counts, positive histology, and a single positive culture.
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- Based on the International Consensus Meeting 2013
- Acute: CRP > 100, ESR normal, Synovial count > 10k, PMN > 90%
- Chronic: CRP > 10, ESR > 30, Synovial count > 3k, PMN > 80% [chronic values lower]
- Synovial CRP > 6.9
- D-dimer 860
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- An enzyme produced by neutrophils in response to infection
- 96.9% accurate
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- A complex aggregation of microorganisms in which cells adhere to each other within a Glycocalyx
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- Makes bacteria 1000-1500× more resistant to antibiotics
- Acts as a scavenging system that traps minerals and nutrients
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- Reversible docking (4/52) - via van der Waals forces
- Irreversible docking - cell adhesion via pili
- Maturation - forms columns, mushrooms and streamer shapes
- Dispersion - spreading and colonizing new surfaces
- All orchestrated through "quorum sensing" - a process by which bacteria signal one another to activate and proliferate via signaling molecules
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- Tsukayama Classification by chronicity and mechanism
- Positive intra-operative cultures only
- Early postoperative infection (within 4 weeks of operation)
- Late acute hematogenous infection (after asymptomatic period but with symptoms lasting < 4 weeks)
- Late chronic infection (> 4 weeks, presents with features of chronicity - sinus tract, abscess, local edema)
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- Withhold antibiotics if patient is stable
- Perform aspiration in operating theater under aseptic technique
DEFINITIVE MANAGEMENT SCENARIOS
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- This is an acute infection within 3 weeks
- We can perform the DAIR (debridement, antibiotics and implant retention) procedure if we meet other criteria: stable implant intraoperatively, non-virulent bacteria with available antibiotic treatment, and no sinus tracts
- According to Sendi et al. in 2017 (on infected THR), if the patient meets all 4 criteria, there is a 90% success rate
sendi2017.pdf397.2KB
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- CPG by ID Society of America 2013 - 4 criteria:
- < 3 weeks of symptoms to prevent biofilm formation OR within 30 days of prosthesis implantation
- Stable implant
- Pathogen susceptible to antibiotics
- No sinus tract or abscess
cis803.pdf629.4 KB
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- Complete synovectomy, exchange of liner, and drain insertion
- Send off odd number of cultures
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- KLIC score - Kidney, Liver, Index Surgery, Cemented Prosthesis, C-reactive Protein
- Prognostic factors for failure include: chronic renal failure, liver cirrhosis, high CRP (indicating high infection load), previous revision surgery, or cemented implant
- Maximum score is 9.5
- High risk > 7 points - failure rate of 60%
- Low risk < 2 points - failure rate of 33%
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- Repeat DAIR procedures have lower success rates compared to initial attempts
- Toh Rui Xiang et al. demonstrated that repeat DAIRs, ESR elevation > 107.5, and S. aureus PJI are significant predictors of treatment failure, suggesting that 2-stage revision is more appropriate in these cases
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- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6571822/
- In pooled analyses of observational studies, cemented fixations were associated with an increased overall PJI risk compared to uncemented fixations.
- However, in the first six months, uncemented fixations showed higher PJI risk compared to all cemented fixations.
- Compared to antibiotic-loaded cemented fixations, plain cemented fixations were associated with an increased PJI risk
- Summary: First 6 months - uncemented higher risk. Overall - cemented higher risk. Plain cement higher risk than antibiotic-loaded cement.
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- I will perform a two-stage revision
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- Can use revision acronym EE (exposure, extraction)
- Prepare equipment as in revision THR
- Need to consider SOFT TISSUE - may need flap coverage after excising sinuses and infected skin
- Number of samples? > 3 but less than 6 (Parvizi international consensus 2013)
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- E, RRR
- Examine and address bone loss (AORI)
- Replant with suitable fixation (zonal fixation technique)
- Need to be concerned about stability - infection may affect the collaterals
- May need LCCK or a Hinged Knee!
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- Use of ultrasound to increase culture yield.
- Parvizi international consensus 2013 – Not for routine use. Only for suspected or proven PJI where aspiration yields no culture OR patient was given antibiotics within last 2 weeks
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- Antibiotic choice = Heat stable
- Vancomycin (1-4g per 40g of cement) and gentamicin or Tobramycin (2.4 to 8.4g per 40g cement)
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- 1st phase - first 10 hours, 30% released
- 2nd phase - 2 weeks, 60% released
- 3rd phase - 2-10th week, final 10% released
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- It's acceptable due to the concept of MIC (minimum inhibitory concentration)
- The high local concentration of antibiotic can kill bacteria despite apparent resistance
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- (+) Systematic review by Guild et al. 2014 shows dynamic spacers provide increased ROM, reduced re-infection rate, facilitated reimplantation and less bone loss
- Can potentially be left in-situ longer if patient isn't ready for second stage
- (-) Contraindications for articulating spacer:
- 1. Incompetent collaterals (unstable knee) → may lead to dislocation
- 2. Poor soft tissue requiring flap coverage (needs immobilization)
- 3. Massive bone loss
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- All-cement spacer vs real-component spacers
- Real component spacer also uses cement for fixation, but contains lower total antibiotic amount than all-cement spacers
- Usually metal femur, all-PE tibia component (but can also use tibia metal) - see pictures below
- Advantages of real-component spacers:
- No difference in ROM between the two types
- Real-component has faster operative time and less blood loss
- Potentially easier reimplantation in second stage
- If patient becomes too frail for second stage but copes well with the real-component spacer, they can continue to be mobile
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- Not mixed in vacuum = high porosity = increased antibiotic concentration, higher antibiotic elution but reduced cement strength
- Mixed in vacuum = lower porosity = reduced antibiotic concentration/elution, but can be used as weight-bearing spacer
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- Full weight bearing for both articulating and static spacers.
- Brace for 6 weeks to allow soft tissue to settle and scar down.
- For articulating spacers, allow full range of motion within the brace.
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- Requires collaboration with plastic surgery colleagues
- Procedure sequence: First stage explant → relook until negative cultures → flap coverage → second stage through flap.
- Consider risks to the flap during second stage. Work with plastic surgery colleagues to plan optimal incision.
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- 1 pack of cement equals 40g
- Can add up to 4g of vancomycin powder per pack
- If antibiotic exceeds 10% of cement volume, mechanical properties may be compromised
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- Levofloxacin + Rifampicin is effective for Staphylococcus aureus infections
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- No consensus, varying from 2 weeks to several months
- MDT with ID giving culture-directed antibiotics for 6 weeks with trending of inflammatory markers → 2 weeks antibiotic-free period → Reimplantation
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- Advantages: faster rehabilitation and shorter hospital stay
- Studies show similar re-infection rates, but results come from high-volume centers.
- Systematic review by Thakrar et al. (JBJS 2019) concludes it's a plausible treatment option in the absence of:
- immunocompromise and
- concurrent sepsis
- resistant bacteria
- sinus tract.
- However, in my practice I will proceed with conventional two-staged procedure
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- Single-stage procedure with articulating spacer as definitive treatment plus antibiotic suppression
- Above knee amputation
- Arthrodesis
- Excision arthroplasty
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- If PJI is suspected, I will proceed with debridement and frozen section analysis as per the MSIS 2018 consensus paper, evaluating three key findings:
- Pus presence
- Bacteria under histological examination
- Neutrophil count
- 400/5/5
- The Musculoskeletal Infection Society diagnostic criterion for periprosthetic joint infection is "greater than five neutrophils per high-power field in five high-power fields observed from histologic analysis of periprosthetic tissue at ×400 magnification."
- If multiple intraoperative frozen sections are negative and the implant is stable, I will perform debridement and liner exchange.
- If clinical suspicion remains high (e.g., red, swollen knee), I will proceed with a two-stage revision. For patients with poor comorbidities, liner exchange with antibiotic suppression is an alternative.
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- Resection arthroplasty
- Fusion
PREVENTION
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- Elevated BMI
- Pre-operative anemia
- Diabetes mellitus
- Intra-articular injection within 3 months - Avila et al. 2022 systematic review and meta-analysis
- Multiple injections - 2% infection rate (single injection) vs 6% (multiple injections, Chambers et al.)
- MRSA colonization
- Rheumatoid arthritis - DMARDS
- Smoking
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- Screen for MRSA - decolonize as necessary. How do you Decolonise MRSA in preop patients?
- For RA patients, stop DMARDS before surgery (consensus)
- If UTI present or symptomatic - screen urine. Otherwise, no role for routine urine screening (consensus)
- Control diabetes - target Hba1c < 7% (consensus)
- Consider delaying surgery if BMI > 40 (higher PJI risk)
- Screen for preoperative anemia (higher risk factor)
- Delay surgery if recent intra-articular injections within 3 months (higher risk)
- Counsel patients on smoking cessation
- Before elective arthroplasty, screen patients for active dental infection (consensus statement)
- OT design factors
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- Appropriate skin preparation
- Meticulous soft tissue handling
- Operating theater design considerations: laminar flow, body exhaust systems (controversial)
- Change gloves before incision/handling of implants
- Minimize operative time
- Reference: Lidwell study
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- Appropriate wound care
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- Follow institution's "national dental center guidelines"
- MSIS 2013 consensus
- Lifelong post-replacement prophylaxis for high-risk patients (high risk = inflammatory arthritis, immunosuppression, insulin-dependent DM, major systemic infection, hemophilia)
- 2 year post replacement prophylaxis for other patients
- Choice of antibiotic: Amoxicillin 2g 1 hour before procedure. Single dose only prior to dental procedure
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The fruit of the righteous is a tree of life, and whoever captures souls is wise. Proverbs 11:30