PERIPROSTHETIC JOINT INFECTION (PJI) AFTER THA
MSIS/ICM Criteria | DAIR vs Two-Stage | Organism-Specific Treatment
TIMEFRAME CLASSIFICATION
Critical Must-Knows
- MSIS/ICM 2018 criteria - major and minor criteria for PJI diagnosis
- Two-stage revision is gold standard for chronic PJI (90% success)
- DAIR indications: acute (under 3 weeks), stable implant, sensitive organism
- Never use cement spacer as permanent implant - toxicity risk
- Organism identification critical - culture before antibiotics when possible
Examiner's Pearls
- "MSIS 2018: 1 major criterion OR 4 minor criteria = definite PJI
- "Synovial alpha-defensin has best diagnostic accuracy (sens 97%, spec 97%)
- "DAIR success under 50% - use strict criteria
- "Biofilm formation makes eradication without removal very difficult
- "S. aureus and resistant organisms require more aggressive treatment
Critical PJI Exam Points
Know MSIS Criteria
Major criteria (1 equals PJI): two positive cultures of same organism OR sinus tract communicating with joint. Minor criteria (4 equals PJI): elevated serum markers, elevated synovial markers, positive histology, single positive culture. This is exam gold.
DAIR Is Not Magic
DAIR success is under 50% overall. Only use in acute infections (under 3 weeks), stable implants, and sensitive organisms. Most chronic PJI requires implant removal. Choosing wrong treatment leads to failure and patient harm.
Two-Stage Gold Standard
Two-stage revision remains the gold standard for chronic PJI with success rates over 90% for sensitive organisms. Stage 1: resection, spacer, antibiotics. Stage 2: reimplantation after infection clearance (typically 6-12 weeks).
Culture Before Antibiotics
Always attempt to identify the organism before starting antibiotics. Hold antibiotics for 2 weeks before aspiration if possible. Culture-negative PJI has worse outcomes - harder to target treatment.
Quick Decision Guide - PJI Treatment Algorithm
| Timing | Clinical Features | Implant Status | First-Line Treatment |
|---|---|---|---|
| Acute postop (under 3 weeks) | Acute symptoms, single organism | Well-fixed components | DAIR (debridement, antibiotics, implant retention) |
| Subacute/chronic (over 3 weeks) | Indolent symptoms or late presentation | Any implant fixation | Two-stage revision (resection, spacer, reimplantation) |
| Acute hematogenous (over 2 years) | Acute symptoms, identifiable source | Well-fixed, no prior infection | DAIR possible if under 3 weeks from symptom onset |
| Any timing | Resistant organism (MRSA, fungi) | Any implant status | Two-stage or resection arthroplasty (salvage) |
| Any timing | Sinus tract present | Any implant status | Implant removal mandatory (two-stage or resection) |
MSIS 2018 - Major Criteria
Memory Hook:SINUS - one major criterion is sufficient for definite PJI diagnosis
MSIS 2018 - Minor Criteria (Need 4 for Definite PJI)
Memory Hook:MINOR - need 4 minor criteria to diagnose PJI without major criteria
DAIR - Strict Criteria for Success
Memory Hook:DAIR has strict indications - if not met, use two-stage revision
TWO-STAGE - Gold Standard for Chronic PJI
Memory Hook:TWO-STAGE is comprehensive and time-intensive but has best success rates
Overview and Epidemiology
Periprosthetic joint infection (PJI) is one of the most devastating complications following total hip arthroplasty. Despite advances in prevention, PJI remains a leading cause of early revision and has profound impact on patient outcomes.
Epidemiology:
- Primary THA: 1-2% infection rate
- Revision THA: 3-5% infection rate (higher risk)
- Increasing incidence despite improved prevention strategies (likely due to higher-risk patients)
- Costs: PJI treatment costs 3-4 times more than primary arthroplasty
Risk factors:
Modifiable:
- Obesity (BMI over 35)
- Diabetes (HbA1c over 7%)
- Smoking
- Malnutrition (albumin under 3.5 g/dL)
- Immunosuppression (steroids, biologics)
- Active infection elsewhere
Non-modifiable:
- Rheumatoid arthritis
- Prior surgery at same site
- Male gender
- Advanced age
These patient factors should trigger optimization protocols preoperatively.
The Biofilm Problem
Biofilm formation is the key pathophysiology of PJI. Bacteria adhere to implant surface and produce extracellular matrix (biofilm). This protects bacteria from antibiotics (1000x higher MIC) and immune system. This is why implant removal is usually necessary for chronic PJI - antibiotics cannot penetrate established biofilm.
Pathophysiology and Microbiology
Routes of infection:
-
Direct inoculation (most common for early PJI)
- Intraoperative contamination
- Postoperative wound complications
- Accounts for majority of early infections
-
Hematogenous spread (late PJI)
- Dental procedures
- Urinary tract infections
- Skin/soft tissue infections
- GI sources (endoscopy, diverticulitis)
-
Contiguous spread (rare)
- Adjacent osteomyelitis
- Septic hip (pre-existing)
Biofilm development stages:
- Bacteria adhere to implant surface
- Mediated by surface proteins and conditioning layer
- Critical window for prevention
- Bacterial multiplication
- Microcolony formation
- Begin extracellular matrix production
- Mature biofilm with complex architecture
- Protective extracellular matrix
- Drastically reduced antibiotic penetration
- Bacteria shed from biofilm
- Can seed new locations
- Chronic inflammation and bone resorption
Biofilm Timeframe
Biofilm maturation takes 3-4 weeks. This is why DAIR (implant retention) only works in acute infections (under 3 weeks). After biofilm matures, antibiotics cannot effectively penetrate, and implant removal becomes necessary.
Organism-specific considerations:
Organism Characteristics and Treatment Implications
| Organism | Virulence | Biofilm | Treatment Challenge |
|---|---|---|---|
| S. aureus (MSSA) | High | Strong | Aggressive, often needs implant removal |
| MRSA | High | Very strong | Two-stage mandatory, prolonged antibiotics |
| CoNS (S. epidermidis) | Low | Very strong | Indolent presentation, strong biofilm producer |
| Streptococcus | Moderate | Weak | Better success with DAIR if caught early |
| Enterococcus | Low-Moderate | Moderate | Often resistant, difficult to treat |
| Gram-negatives | Variable | Variable | Often resistant, polymicrobial common |
| Fungi (Candida) | Low | Moderate | Requires antifungals, often two-stage or resection |
Classification Systems
Temporal classification (Tsukayama/Fitzgerald & Steinberg):
| Type | Timing | Presentation | Typical Organisms |
|---|---|---|---|
| I. Early postoperative | Under 3 months | Acute wound inflammation | S. aureus, Gram-negatives |
| II. Delayed/chronic | 3-24 months | Indolent, pain, loosening | CoNS, P. acnes |
| III. Late hematogenous | Over 24 months | Acute symptoms, well-fixed implant | S. aureus, Streptococcus |
| IV. Positive intraoperative | During revision | Unexpected positive cultures | Variable |
Classification Guides Treatment
The temporal classification directly guides treatment choice. Early (Type I) and acute hematogenous (Type III, if under 3 weeks symptoms) may be suitable for DAIR. Delayed/chronic (Type II) almost always requires two-stage revision.
McPherson staging (host and extremity factors):
A (Good host):
- Healthy, no comorbidities
- Good nutrition, no immunosuppression
- Best prognosis
B (Compromised host):
- Diabetes, obesity, smoking
- Local wound issues
- Intermediate prognosis
C (Severe compromise):
- Significant immunosuppression
- Active malignancy, ESRD
- Multiple failed surgeries
- Poor prognosis, consider salvage
Host grade affects antibiotic duration and treatment aggressiveness.
Clinical Presentation and Assessment
Clinical presentation varies by timing:
Clinical Presentations
| Timing | Symptoms | Key Features |
|---|---|---|
| Acute (under 3 months) | Fever, wound drainage, erythema | Clear signs of infection, systemic symptoms |
| Subacute (3-24 months) | Pain, stiffness, mechanical symptoms | May mimic aseptic loosening, subtle presentation |
| Chronic (over 24 months, hematogenous) | Acute pain in previously well-functioning THA | Identifiable infection source elsewhere |
History taking:
- Timing of symptoms relative to surgery
- Previous function of the THA (was it ever pain-free?)
- Wound complications postoperatively
- Recent infections or procedures (dental, UTI)
- Risk factors: diabetes, immunosuppression, prior surgery
- Prior antibiotic use (affects culture yield)
Physical examination:
Sinus Tract = Infection
A sinus tract communicating with the prosthesis is pathognomonic for infection (MSIS major criterion). Even without other signs, this mandates treatment for PJI.
Examination findings:
- Wound erythema, warmth, swelling
- Sinus tract or wound drainage
- Pain with ROM (even passive)
- Reduced ROM (contracture from chronic inflammation)
- Previous surgical scars
- Systemic signs (fever, sepsis in severe cases)
Subtle Chronic PJI
Chronic PJI can mimic aseptic loosening. Any patient with painful THA (especially if never pain-free postop or pain after pain-free interval) should be worked up for infection. Don't assume aseptic loosening without ruling out PJI.
Diagnostic Investigations
MSIS/ICM 2018 Criteria for PJI:
Major criteria (ONE required for definite PJI):
- Two positive cultures of the same organism from separate samples
- Sinus tract communicating with the prosthesis
Minor criteria (FOUR required for definite PJI if no major criteria):
| Minor Criterion | Threshold | Points if met |
|---|---|---|
| Elevated serum CRP | Over 10 mg/L | 1 |
| Elevated serum ESR | Over 30 mm/hr | 1 |
| Elevated synovial WBC | Over 3000 cells/µL | 2 |
| Elevated synovial PMN% | Over 70% | 1 |
| Positive alpha-defensin | Qualitative positive | 3 |
| Positive leukocyte esterase | ++ or +++ | 3 |
| Elevated synovial CRP | Over 6.9 mg/L | 1 |
| Single positive culture | One organism | 2 |
| Positive histology | Over 10 PMN/HPF (5 HPF) | 3 |
Scoring System
The 2018 MSIS criteria use a scoring system: score of 6 or more = definite PJI. Alpha-defensin, LE (at ++ or +++), and histology are worth 3 points each. Synovial WBC over 3000 is worth 2 points. This is exam-critical knowledge.
Diagnostic workup algorithm:
First-line blood tests:
- ESR (over 30 mm/hr suggestive)
- CRP (over 10 mg/L suggestive)
- CBC with differential (leukocytosis less sensitive)
- D-dimer (research, not yet standard)
Limitations:
- ESR/CRP can be elevated in aseptic inflammation
- Sensitivity 80-90%, specificity 70-80%
- More useful for monitoring treatment response
Utility:
- Elevated markers prompt further workup
- Normal markers don't rule out PJI (especially low-virulence)
- Trending markers guides treatment response
Serum markers are screening tests but not diagnostic alone.
Diagnostic algorithm summary:
- Clinical suspicion → Serum ESR/CRP
- If elevated or high suspicion → Hip aspiration (off antibiotics if possible)
- Aspiration: cell count, culture, alpha-defensin
- Apply MSIS criteria for diagnosis
- If diagnosis confirmed → Plan treatment based on timing and organism
- Intraoperative cultures confirm and guide antibiotic therapy
Management Algorithm
PJI treatment options:
-
Debridement, Antibiotics, Implant Retention (DAIR)
- Acute infection (under 3 weeks)
- Stable implant
- Sensitive organism
-
One-stage revision
- Single surgery: remove components, debride, reimplant
- Selective use (Europe more than US)
- Known sensitive organism
-
Two-stage revision (GOLD STANDARD)
- Stage 1: resection, debridement, spacer
- Antibiotics 6-12 weeks
- Stage 2: reimplantation
- Highest success rate for chronic PJI
-
Resection arthroplasty (salvage)
- Permanent spacer or Girdlestone
- Multiple failed revisions
- Non-reconstructable bone loss
- Severe medical comorbidities
-
Suppressive antibiotics only
- Medically unfit for surgery
- Patient refuses surgery
- Palliative intent
Treatment choice depends on timing, organism, implant fixation, and host factors.
Surgical Technique
Debridement, Antibiotics, Implant Retention (DAIR)
Surgical steps:
- Approach: Use previous surgical incision
- Exposure: Full capsulotomy, inspect entire joint
- Debridement:
- Complete synovectomy (remove ALL synovium)
- Debride any necrotic tissue
- Inspect component-bone interfaces
- Remove loose debris
- Component assessment:
- Test stability (push-pull test)
- Inspect for loosening, wear
- If loose - convert to two-stage
- Modular exchange (critical):
- Remove femoral head
- Remove acetabular liner
- New head and liner (do NOT reuse)
- Check neck-liner impingement
- Irrigation:
- Copious irrigation (minimum 6 liters)
- Normal saline (no additives)
- Pulsatile lavage for deeper areas
- Cultures: Minimum 5 tissue samples from different locations
- Closure: Layered closure over drain
Modular Exchange Essential
Always exchange ALL modular components during DAIR (head and liner). Biofilm forms on these surfaces. Reusing modular components dramatically increases DAIR failure rate.
Antibiotic Therapy
Organism-specific antibiotic selection:
First-Line Antibiotic Choices by Organism
| Organism | First-Line IV | Oral Suppression | Duration |
|---|---|---|---|
| MSSA | Flucloxacillin or cefazolin | Cefalexin + rifampicin | IV 4-6 weeks, oral 3-6 months |
| MRSA | Vancomycin | Linezolid, cotrimoxazole, or doxycycline | IV 6 weeks minimum, oral 6-12 months |
| CoNS | Vancomycin (often resistant to beta-lactams) | Cefalexin (if sensitive) + rifampicin | IV 4-6 weeks, oral 3-6 months |
| Streptococcus | Penicillin or ceftriaxone | Amoxicillin | IV 2-4 weeks, oral 3 months |
| Enterococcus | Ampicillin + gentamicin (synergy) | Amoxicillin | IV 4-6 weeks, oral 3-6 months |
| Gram-negative rods | Fluoroquinolone (ciprofloxacin) | Ciprofloxacin + rifampicin | IV 4 weeks, oral 6 months minimum |
| Polymicrobial | Broad-spectrum (vancomycin + pip-tazo) | Based on sensitivities | Extended duration, tailored to organisms |
Key antibiotic principles:
Rifampicin Rules
Rifampicin enhances biofilm penetration and should be used for Staph infections (MSSA, MRSA, CoNS) when implant is retained (DAIR) or after reimplantation. Never use rifampicin monotherapy - resistance develops rapidly. Always combine with another active agent.
General antibiotic protocol:
-
Stage 1 (resection) to Stage 2 (reimplantation):
- IV antibiotics: 4-6 weeks post-stage 1
- Oral antibiotics: Continue until stage 2 (or stop 2-6 weeks before for antibiotic holiday)
- Choice based on culture and sensitivities
-
After Stage 2 (reimplantation):
- IV antibiotics: 2-4 weeks
- Oral suppression: 3-6 months minimum
- Some advocate 12 months for S. aureus/MRSA
- Infectious disease consultation recommended
Australian context (PBS):
- Vancomycin covered for severe infections
- Linezolid requires authority for PJI
- Daptomycin available for MRSA/VRE (authority)
- Consult local antimicrobial stewardship
Culture-Negative PJI
Culture-negative PJI (7-10% of cases) has worse outcomes. Causes: prior antibiotics, fastidious organisms, biofilm. Treat empirically with broad-spectrum (vancomycin + pip-tazo or meropenem) and consider extended culture incubation, molecular diagnostics, or fungal cultures.
Complications
Complications of PJI and Treatment
| Complication | Incidence | Prevention/Management |
|---|---|---|
| Recurrent infection | 10-20% (two-stage), 20-40% (DAIR) | Adequate debridement, appropriate antibiotics, good host optimization |
| Bone loss | Common in chronic PJI | Staged reconstruction, impaction grafting, revision components |
| Spacer complications | 10-15% (fracture, dislocation) | Articulating spacer preferred, patient education on weight-bearing |
| Antibiotic toxicity | 5-15% (renal, hepatic, GI) | Drug level monitoring, renal function checks, ID consultation |
| Persistent pain | 20-30% even after successful treatment | Set realistic expectations, consider salvage if infection cleared |
| Death | 1-2% (higher in elderly, comorbid) | Early recognition, aggressive treatment, optimize comorbidities |
Recurrent infection:
- Most devastating complication
- Risk factors: resistant organisms, immunocompromised host, inadequate debridement
- Management: repeat two-stage, consider salvage (resection arthroplasty)
Antibiotic-related complications:
- Vancomycin: nephrotoxicity (monitor trough levels, creatinine)
- Aminoglycosides: oto- and nephrotoxicity (avoid in renal impairment)
- Rifampicin: hepatotoxicity, drug interactions (LFTs monitoring)
- Fluoroquinolones: tendon rupture, avoid in elderly if possible
Postoperative Care and Rehabilitation
After DAIR:
- Standard THA precautions
- Early mobilization (POD 1-2)
- IV antibiotics
- Monitor wound closely
- Continue IV antibiotics (home IV via PICC if stable)
- Transition to oral antibiotics at 4-6 weeks
- Progressive weight-bearing
- Outpatient physiotherapy
- Oral suppressive antibiotics
- Continue mobilization and strengthening
- Monitor inflammatory markers monthly
- Continue oral antibiotics (per ID)
- Monitor for recurrence
- Gradual return to activities
After Two-Stage Revision:
Stage 1 (resection/spacer):
- Weight-bearing: protected (PWB with walker/crutches)
- Articulating spacer allows mobilization
- IV antibiotics in hospital then home PICC
- Manage expectations - significant disability during this phase
- Spacer is temporary - not a permanent solution
Interval between stages:
- Continue antibiotics per protocol
- Monitor inflammatory markers
- Aspirate hip off antibiotics before stage 2
- Optimize medical comorbidities
- Nutritional optimization (albumin, vitamin D)
Stage 2 (reimplantation):
- Standard THA precautions
- Early mobilization (POD 1-2)
- WBAT if stable fixation
- IV antibiotics 2-4 weeks
- Transition to oral suppression 3-6 months
Long-term surveillance:
- Monitor inflammatory markers at 3, 6, 12 months
- Annual clinical and radiographic review
- Any new pain/symptoms → rule out recurrence
- Patient education on dental prophylaxis
Outcomes and Prognosis
Treatment-specific outcomes:
| Treatment | Success Rate | Functional Outcome | Complications |
|---|---|---|---|
| DAIR | 30-60% | Good if successful | High reinfection |
| One-stage | 80-85% | Good | Moderate reinfection |
| Two-stage | 90-95% (sensitive) | Good to fair | Lowest reinfection |
| Resection | 95% infection control | Poor function | Pain, instability |
Prognostic factors for success:
Favorable:
- Sensitive organisms (Streptococcus best)
- Healthy host (no immunosuppression)
- Early diagnosis and treatment
- Good soft tissue envelope
- Adequate bone stock
Unfavorable:
- MRSA, resistant Gram-negatives, fungi
- Immunosuppressed host (steroids, biologics)
- Multiple prior surgeries
- Extensive bone loss
- Polymicrobial infection
- Culture-negative PJI
Function After Two-Stage
Even with successful infection eradication, functional outcomes after two-stage revision are inferior to primary THA. Patients have longer recovery, more pain, worse ROM, and lower satisfaction scores. Setting realistic expectations is critical.
Long-term considerations:
- PJI survivors have increased mortality compared to matched controls
- Quality of life significantly impacted
- Economic burden substantial (lost work, caregiver needs)
- Psychological impact (depression, anxiety common)
Prevention Strategies
Preoperative optimization:
Target thresholds:
- HbA1c under 7% (diabetics)
- BMI under 35 (consider weight loss if over 40)
- Albumin over 3.5 g/dL (nutritional status)
- Smoking cessation 4+ weeks preop
- Optimize RA/inflammatory disease (minimize steroids)
Screening and treatment:
- Screen and treat MRSA colonization (nasal mupirocin)
- Clear remote infections (dental, skin, UTI)
- Optimize immunosuppression (hold biologics perioperatively per protocol)
Medical optimization reduces infection risk by 50% or more in high-risk patients.
Australian context - prevention:
- ACSQHC National Safety and Quality Health Service Standards
- Surgical site infection surveillance programs
- Perioperative antibiotic guidelines (Therapeutic Guidelines: Antibiotic)
- Preoperative optimization pathways in major centers
Evidence Base
- Updated diagnostic criteria with scoring system. Major criteria (sinus tract or 2 positive cultures) OR score of 6+ from minor criteria equals definite PJI. Alpha-defensin worth 3 points (highest). Provides standardized, evidence-based definition used worldwide.
- Systematic review comparing one-stage and two-stage revision. Two-stage success: 87.7% (range 73-100%). One-stage success: 82.6% (range 70-100%). No significant difference in meta-analysis but two-stage used for more severe infections.
- Demonstrated that biofilm formation on implants protects bacteria from antibiotics and immune system. Sonication of removed implants increased culture sensitivity from 60% to 75%. Biofilm is key reason implant removal is necessary for chronic PJI.
- Comprehensive treatment guidelines from Infectious Diseases Society of America. Recommend 4-6 weeks IV antibiotics for most PJI. Rifampicin should be added for Staph infections with retained implants. Recommend ID consultation for all PJI cases.
- Large cohort study of DAIR outcomes. Success rates: Streptococcus 74%, Staph 50%, MRSA 41%, Gram-negatives 58%. Predictors of failure: symptoms over 3 weeks, S. aureus, prior surgery. DAIR should be used selectively with strict criteria.
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Early Postoperative PJI
"A 68-year-old man is 10 days post-primary THA. He develops increasing hip pain, fevers to 38.5°C, and the wound has serous drainage. ESR 65, CRP 120. What is your assessment and management?"
Scenario 2: Chronic PJI - Two-Stage Candidate
"A 72-year-old woman had a primary THA 18 months ago. She has had persistent pain since surgery, never pain-free. X-rays show subtle periosteal reaction and focal osteolysis. ESR 45, CRP 35. Hip aspiration grows coagulase-negative Staphylococcus (CoNS) from 2 of 3 samples. How do you manage this?"
Scenario 3: Late Hematogenous PJI
"A 65-year-old man had a well-functioning THA 5 years ago (pain-free until now). He presents with 1 week of acute severe hip pain and fever following a dental extraction 2 weeks ago. ESR 75, CRP 95. X-rays show well-fixed components with no loosening. Hip aspiration grows Streptococcus viridans. What is your management?"
Timing Critical
MCQ Practice Points
MSIS 2018 Major Criteria
Q: What are the two major criteria for PJI diagnosis in MSIS 2018? A: (1) Sinus tract communicating with the prosthesis, OR (2) Two positive cultures of the same organism from separate samples. Either ONE major criterion is sufficient for definite PJI diagnosis.
MSIS Minor Criteria Scoring
Q: Which minor criteria are worth 3 points each in the MSIS 2018 scoring system? A: (1) Alpha-defensin (qualitative positive), (2) Leukocyte esterase (++ or +++), (3) Histology (over 10 PMN/HPF in 5 high-power fields). Score of 6 or more equals definite PJI.
DAIR Indications
Q: What are the strict criteria that must ALL be met for DAIR to be appropriate? A: (1) Acute infection (under 3 weeks symptoms OR under 3 months from surgery), (2) Stable/well-fixed implant, (3) Known organism with sensitivities, (4) No sinus tract, (5) Reasonable host (not severely immunocompromised).
Two-Stage Success Rates
Q: What are the success rates for two-stage revision based on organism? A: Sensitive organisms (Strep, MSSA): 90-95%. S. aureus: 85-90%. Resistant organisms (MRSA, resistant GNR): 70-80%. Fungi: under 70%. Two-stage has highest success of all treatments.
Biofilm Timing
Q: Why does DAIR only work in acute infections (under 3 weeks)? A: Biofilm maturation takes 3-4 weeks. Mature biofilm protects bacteria from antibiotics (increases MIC by 1000-fold) and immune system. Before biofilm matures, antibiotics can penetrate. After maturation, implant removal is required for eradication.
Rifampicin Use
Q: When should rifampicin be used in PJI treatment? A: For Staphylococcus species (S. aureus, MRSA, CoNS) when implant is retained (DAIR or after reimplantation). Rifampicin enhances biofilm penetration. Never use as monotherapy - always combine with another active agent to prevent resistance.
Culture-Negative PJI
Q: What are the main causes of culture-negative PJI and how is it managed? A: Causes: (1) Prior antibiotics (most common), (2) Fastidious organisms (slow-growing), (3) Biofilm (organisms in biofilm less culturable). Manage with: extended culture incubation (14 days), molecular diagnostics, sonication of removed implants, empiric broad-spectrum antibiotics (vancomycin + broad Gram-negative coverage).
Australian Context
Epidemiology:
- AOANJRR tracks PJI as revision indication
- Primary THA revision for infection: 1.1% at 10 years
- Revision THA re-revision for infection: 4.2% at 10 years
- Infection is 3rd most common cause of revision (after loosening and dislocation)
Management pathways:
- Tertiary referral centers have PJI multidisciplinary teams
- Orthopaedics, Infectious Diseases, Microbiology collaboration
- Specialized units: RPA Sydney, Austin Melbourne, PA Brisbane
Antibiotic considerations (Australian PBS):
- Vancomycin: covered for severe infections
- Linezolid: authority required for PJI (MRSA/VRE)
- Daptomycin: authority required, alternative for MRSA
- Ceftriaxone: covered, good Strep coverage
- Ciprofloxacin: PBS listed, use for Gram-negatives with rifampicin
Therapeutic Guidelines (eTG):
- Follow eTG Antibiotic guidelines for PJI
- Recommend ID consultation for all PJI cases
- Emphasize antibiotic stewardship (avoid prolonged broad-spectrum)
Prevention initiatives:
- National Safety and Quality Health Service Standards (NSQHS)
- Surgical site infection surveillance
- Antibiotic prophylaxis protocols
- Preoperative optimization pathways
Exam Context
Be prepared to discuss MSIS 2018 diagnostic criteria (major and minor with scoring). Know treatment algorithm: DAIR for acute with strict criteria, two-stage for chronic (gold standard). Understand organism-specific management (especially S. aureus vs Strep). Know antibiotic principles including rifampicin use for Staph with retained implants.
PERIPROSTHETIC JOINT INFECTION (PJI) AFTER THA
High-Yield Exam Summary
MSIS 2018 MAJOR CRITERIA (ONE = DEFINITE PJI)
- •1. Sinus tract communicating with prosthesis
- •2. Two positive cultures of same organism (separate samples)
- •Either ONE major criterion alone = definite PJI diagnosis
- •No further workup required if major criterion present
MSIS 2018 MINOR CRITERIA (SCORE 6+ = DEFINITE PJI)
- •Elevated serum CRP (over 10 mg/L) = 1 point
- •Elevated serum ESR (over 30 mm/hr) = 1 point
- •Elevated synovial WBC (over 3000) = 2 points
- •Elevated synovial PMN% (over 70%) = 1 point
- •Positive alpha-defensin = 3 points (HIGHEST)
- •Positive LE (++ or +++) = 3 points
- •Elevated synovial CRP (over 6.9 mg/L) = 1 point
- •Single positive culture = 2 points
- •Positive histology (over 10 PMN/HPF, 5 fields) = 3 points
DAIR STRICT CRITERIA (ALL MUST BE MET)
- •Acute: under 3 weeks symptoms OR under 3 months from surgery
- •Stable/well-fixed implant (no loosening)
- •Known organism with sensitivities
- •No sinus tract present
- •Healthy host (not severely immunocompromised)
TWO-STAGE REVISION (GOLD STANDARD)
- •Stage 1: Complete removal, debridement, antibiotic spacer
- •IV antibiotics 4-6 weeks, oral until stage 2
- •Antibiotic holiday 2-6 weeks before stage 2
- •Aspirate off antibiotics before stage 2
- •Stage 2: Reimplant when infection cleared (normal markers, negative aspirate)
- •Success: 90-95% sensitive organisms, 85% MSSA, 70-75% resistant
ORGANISM-SPECIFIC TREATMENT
- •MSSA: Flucloxacillin IV → cefalexin + rifampicin PO
- •MRSA: Vancomycin IV → linezolid/cotrimoxazole PO (longer duration)
- •Streptococcus: Penicillin/ceftriaxone (best DAIR success 70-80%)
- •Enterococcus: Ampicillin + gentamicin (synergy)
- •Gram-negatives: Ciprofloxacin + rifampicin
- •Culture-negative: Vancomycin + pip-tazo (broad empiric)
KEY PEARLS AND TRAPS
- •Biofilm matures in 3-4 weeks → why DAIR only works early
- •Rifampicin for Staph with retained implants (never monotherapy)
- •DAIR success 30-60% overall (organism-dependent)
- •Culture before antibiotics (2 weeks off if possible)
- •Never use spacer as permanent implant (cement toxicity)
- •Alpha-defensin best single test (sens 97%, spec 97%)
- •Chronic PJI can mimic aseptic loosening - always rule out infection