Definitions and Classification

Surgical site infections (SSIs) are classified based on depth and timing:

Superficial Incisional SSI:

• Occurs within 30 days of surgery
• Involves only skin and subcutaneous tissue
• Must have at least one of: purulent drainage, organisms from culture, signs of infection (pain, swelling, redness, heat)
• Deliberately opened by surgeon (unless culture negative)

Deep Incisional SSI:

• Occurs within 30 days (no implant) or 90 days (implant present)
• Involves deep soft tissues (fascia, muscle)
• Purulent drainage from deep space or dehiscence
• Abscess or evidence of infection on imaging or re-exploration
• Most concerning in orthopaedics due to implant involvement

Organ/Space SSI:

• Involves anatomic structures opened or manipulated during surgery
• Examples: septic arthritis, osteomyelitis, epidural abscess
• Specific to orthopaedics: prosthetic joint infection, spinal implant infection
• Highest morbidity and often requires implant removal

The classification is critical for surveillance, benchmarking, and quality improvement initiatives. Deep and organ/space SSIs have significantly higher morbidity and costs.

Surgical site infection (SSI) prevention requires a multimodal bundle approach targeting pre-operative, intra-operative, and post-operative phases. Key interventions include antibiotic prophylaxis timing (within 60 minutes of incision), chlorhexidine-alcohol skin preparation, MRSA screening and decolonization for high-risk procedures, and maintaining normothermia and euglycaemia (glucose under 10 mmol/L). Major modifiable risk factors include diabetes (HbA1c over 8%), smoking (minimum 4 weeks cessation), obesity, and prolonged operative duration. SSIs are classified by depth (superficial, deep, organ/space) with extended 90-day surveillance for implant surgery, where deep and organ/space infections may necessitate implant removal.

Screening and Decolonization

MRSA colonization increases SSI risk 2-9 fold in carriers. Screening and decolonization protocols are evidence-based interventions:

Screening Protocol:

• Universal screening for high-risk procedures (arthroplasty, spinal instrumentation)
• Nasal swab PCR testing (rapid results, 24 hours)
• Additional sites for high-risk patients (throat, perineum, wounds)
• Timing: Minimum 1 week before surgery (allows time for decolonization)

Decolonization Regimen (if positive):

• Mupirocin 2% nasal ointment (both nares, twice daily, 5 days)
• Chlorhexidine 4% body wash (daily, 5 days)
• Clean environment (wash bedding, clothing during treatment)
• Re-swab after completion (confirm clearance)

Australian Context: Not universally funded but increasingly adopted for high-risk arthroplasty patients. Cost-effectiveness demonstrated when SSI rates exceed 1%. Some states have mandatory screening programs.

Alternative Regimens:

• Povidone-iodine nasal antiseptic (alternative to mupirocin)
• Chlorhexidine-alcohol body wipes (inpatient convenience)
• Extended courses for recurrent colonization (10 days)

Evidence supports this intervention particularly for MRSA carriers undergoing implant surgery, where it reduces SSI rates by 40-60%.

Appropriate timing of antibiotic prophylaxis is critical for efficacy:

Optimal Timing:

• 30-60 minutes before skin incision (60 minutes for vancomycin due to slow infusion)
• Ensures therapeutic tissue levels at time of bacterial inoculation
• Too early: Antibiotic levels decline before wound closure
• Too late: Bacteria already established in wound

Australian Guidelines (eTG):

• Single dose 30-60 minutes pre-incision for most procedures
• Cefazolin 2g IV (3g if weight greater than 120 kg) standard for clean orthopaedic
• Flucloxacillin 2g IV alternative (narrower spectrum, less resistance pressure)
• Vancomycin 15-20 mg/kg IV (over 60-90 min) if MRSA risk or beta-lactam allergy
• Plus gentamicin 4-6 mg/kg IV for contaminated wounds

Re-dosing Requirements:

• Cefazolin: Every 2-4 hours if surgery exceeds one half-life (2 hours)
• Vancomycin: No re-dosing needed for most cases (long half-life 6-8 hours)
• Gentamicin: Usually single dose sufficient
• After tourniquet release (give dose before inflation, re-dose if multiple tourniquet applications)

Special Circumstances:

• Tourniquet surgery: Administer before tourniquet inflation (ensure wound bed levels)
• Massive transfusion: Re-dose after significant blood loss (greater than 1500 mL)
• Long procedures: Re-dose at 2x half-life intervals
• Revision surgery: Broader spectrum may be indicated (case-dependent)

Documentation:

• Checklist verification (WHO surgical safety checklist)
• Time of administration recorded
• Re-dosing documented in anesthetic record
• Antibiotic type and dose confirmed

The 30-60 minute window is critical. Studies show SSI rates increase 2-fold if antibiotics given after incision or greater than 2 hours before incision.

Skin Preparation

Operating Room Environment

Operating room air quality directly impacts SSI risk in implant surgery:

Standard Operating Room Ventilation:

• Minimum 15 air changes per hour (Australian Standard AS 1668)
• Positive pressure relative to corridors
• HEPA filtration (high-efficiency particulate air)
• Filtered, temperature-controlled air supply
• Appropriate humidity (30-60%)

Laminar Flow Systems:

• Ultra-clean air (less than 10 colony-forming units per cubic meter)
• Unidirectional airflow over surgical field
• 300-400 air changes per hour in laminar zone
• Reduces airborne bacteria by 90-99% vs conventional
• Recommended for arthroplasty and spinal instrumentation

Evidence for Laminar Flow:

• Controversial - some studies show SSI reduction, others no benefit
• Benefit most clear in total joint arthroplasty (older studies)
• May be overcome by modern prophylaxis bundles
• Swedish data suggests benefit (mandatory for arthroplasty)
• UK data mixed (SPARE trial showed no benefit with modern prophylaxis)

Operating Room Discipline:

• Minimize traffic (each person increases bacterial counts)
• Keep doors closed (maintains pressure gradient and air flow)
• Limit personnel (only essential staff in room)
• Restrict entry/exit during critical periods
• No talking directly over open wounds (droplet spread)

Australian Context: Laminar flow not mandated but common in dedicated arthroplasty theaters. AS/NZS 1668 and AS/NZS ISO 14644 set ventilation standards. Increasing use in public and private joint replacement centers.

The debate continues, but consensus supports laminar flow for high-risk implant surgery (arthroplasty, spinal instrumentation) as part of comprehensive infection prevention despite mixed evidence.

Meticulous surgical technique is fundamental to SSI prevention:

Tissue Handling:

• Minimize trauma (gentle retraction, appropriate instruments)
• Preserve blood supply (avoid excessive periosteal stripping)
• Protect soft tissues (no crush injuries from clamps)
• Limit electrocautery use (devitalizes tissue)
• Irrigate regularly (remove debris and bacteria)

Hemostasis:

• Achieve meticulous hemostasis before closure
• Hematoma increases SSI risk 3-fold
• Use appropriate techniques (cautery, topical agents, tourniquet timing)
• Consider tranexamic acid (reduces bleeding and transfusion)
• Post-operative drains if dead space significant (controversial)

Dead Space Management:

• Eliminate dead space where possible (layered closure)
• Tack soft tissues to bone (prevent fluid accumulation)
• Drains for large potential spaces (controversial, may increase infection)
• If using drains, closed suction preferred
• Remove drains early (24-48 hours to minimize infection risk)

Irrigation:

• Copious irrigation before closure (3-9 liters for arthroplasty)
• Normal saline is standard (equal to antibiotic or antiseptic irrigation)
• Pulse lavage may increase soft tissue damage (low pressure preferred)
• Final irrigation after implant insertion and before closure
• Remove all irrigation fluid before closure

Closure:

• Layered closure (reduces dead space)
• Absorbable sutures for deep layers
• Skin closure: Subcuticular preferred (removes SSI risk from superficial sutures/staples)
• Alternatively, staples or sutures (remove at 10-14 days)
• Adhesive strips or glue for skin edge approximation
• Waterproof dressing (prevents bacterial ingress for 48-72 hours)

These technical factors are surgeon-controlled and represent major opportunities to reduce SSI risk through excellence in operative technique.

Wound Care

Post-operative Glucose Control

Post-operative hyperglycemia increases SSI risk even in non-diabetics:

Target Glucose Levels:

• All patients: Less than 10 mmol/L for first 48 hours
• Diabetic patients: 6-10 mmol/L optimal (avoid hypoglycemia)
• Avoid hypoglycemia (less than 4 mmol/L increases complications)

Monitoring:

• Point-of-care glucose testing (fingerstick)
• Minimum every 6 hours for first 24-48 hours (major surgery)
• More frequent if diabetic or insulin infusion (every 2-4 hours)
• Continue until eating normally and glucose stable

Management:

• Sliding scale insulin (reactive approach, less ideal)
• Variable-rate insulin infusion (proactive, better control for major surgery)
• Resume home medications when tolerating oral intake
• Endocrinology consultation for difficult-to-control cases

Non-Diabetic Hyperglycemia:

• Stress response to surgery (cortisol, catecholamines)
• More common in major surgery, long cases, significant trauma
• Treat even in non-diabetics if glucose greater than 10 mmol/L
• Usually resolves as stress response diminishes (48-72 hours)

Evidence: Post-operative hyperglycemia (greater than 10 mmol/L) doubles SSI risk. Each 1 mmol/L increase above 6 mmol/L increases risk 10-20%. Benefits of control seen in diabetic and non-diabetic patients.

Australian Protocol: Many hospitals have post-operative glucose monitoring protocols for major orthopaedic surgery, regardless of diabetic status. Standardized insulin protocols improve consistency and safety.

Post-operative glucose control is an often-overlooked aspect of SSI prevention but has strong evidence and is easily modifiable with proper protocols.

Patient engagement is crucial for early detection and prevention of SSI:

Pre-operative Education:

• Infection signs and symptoms (redness, swelling, warmth, drainage, fever, pain)
• Wound care instructions (keep clean and dry, dressing changes)
• When to contact surgeon (clear criteria)
• Importance of adherence to restrictions (wound protection, activity)
• Role of patient in prevention (hygiene, medication compliance)

Discharge Instructions:

• Written information in plain language
• Visual aids (pictures of normal vs infected wounds)
• 24-hour contact number for concerns
• Follow-up appointment schedule
• Red flags requiring immediate attention

Monitoring Schedule:

• First post-operative visit: 10-14 days (wound check, suture removal)
• Second visit: 6 weeks (clinical and radiographic assessment)
• Additional visits as indicated by symptoms or risk factors
• Patient-initiated contact for concerns (low threshold to call)

Red Flags for Patients:

• Increasing pain after initial improvement
• Fever (greater than 38°C)
• Increasing redness or swelling around wound
• Purulent drainage or foul odor
• Wound dehiscence or separation
• Systemic symptoms (chills, malaise, confusion in elderly)

Barriers to Compliance:

• Health literacy (education level, language)
• Cognitive impairment (elderly, dementia)
• Social support (lives alone, limited assistance)
• Access to healthcare (remote location, transport)

Strategies to Overcome Barriers:

• Interpreter services for non-English speakers
• Family member involvement in education
• Community nursing support for wound care
• Telehealth follow-up for remote patients
• Simplified written materials with pictures

Australian context: Many patients discharged within 1-3 days for arthroplasty (enhanced recovery protocols). This makes patient education and self-monitoring critical as most SSI present after discharge.

Implant Surgery

Antibiotic Stewardship

Appropriate antibiotic use prevents SSI while minimizing resistance development:

Principles of Stewardship:

• Use narrowest spectrum effective antibiotic
• Single dose for clean surgery (additional doses rarely beneficial)
• No routine post-operative antibiotics (prophylaxis only)
• Stop prophylaxis by 24 hours post-operatively (most cases)
• Document clear indication for extended courses

When to Extend Prophylaxis:

• Controversial and generally not recommended
• Possible exceptions: Retained hematoma, prolonged drains (debatable)
• Discuss with infectious disease if considering extension
• Not indicated for fear/anxiety about infection

Avoiding Overuse:

• Treating colonization (positive cultures without infection symptoms)
• Empiric treatment without infection (abnormal labs, low-grade fever)
• Extended durations without clear endpoint
• Broad spectrum without culture guidance

Australian Guidelines (eTG):

• Single dose cefazolin for clean orthopaedic surgery
• Discontinue within 24 hours post-operatively
• No routine prophylaxis after prosthetic joint for dental procedures (controversial, patient-specific decisions)
• Antibiotic choice guided by local resistance patterns

Resistance Concerns:

• MRSA rates increasing with overuse of vancomycin
• Extended-spectrum beta-lactamase (ESBL) organisms
• Multi-drug resistant Gram negatives
• Clostridium difficile from broad-spectrum use

Monitoring:

• Hospital antibiograms (resistance patterns)
• SSI rates (stratified by antibiotic choice)
• C. difficile infection rates (marker of antibiotic overuse)
• Surgeon-specific data (feedback for improvement)

Stewardship requires institutional commitment with pharmacy, infectious disease, and surgical collaboration. Education about resistance is key to changing prescribing culture.

Evidence-Based Bundles

SSI prevention bundles combine multiple evidence-based interventions for synergistic effect:

Core Bundle Elements:

1. Appropriate antibiotic selection and timing (60 minutes pre-incision)
2. Glucose control (less than 10 mmol/L perioperatively)
3. Normothermia (greater than 36°C intraoperatively)
4. Chlorhexidine-alcohol skin preparation
5. Appropriate hair removal (clippers, not razors)
6. Sterile technique and OR discipline

Enhanced Bundle (Implant Surgery): 7. MRSA screening and decolonization 8. Pre-operative chlorhexidine bathing 9. Laminar flow operating rooms 10. Antibiotic-loaded cement (cemented arthroplasty) 11. Intrawound vancomycin (spinal instrumentation) 12. Negative pressure wound therapy (high-risk wounds)

Implementation:

• Checklist-driven (WHO surgical safety checklist + institution-specific)
• Team education and buy-in (surgeons, anesthesia, nursing)
• Audit and feedback (compliance rates, SSI outcomes)
• Continuous quality improvement (PDSA cycles)
• Multidisciplinary ownership (not just surgical)

Evidence: Bundle approaches reduce SSI by 40-60% compared to individual interventions. Compliance with all elements is key - partial compliance provides partial benefit. Checklist use improves compliance dramatically.

Australian Example: Many hospitals have adopted arthroplasty SSI prevention bundles based on international guidelines (AAOS, NICE, CDC). State-based quality improvement initiatives track compliance and outcomes.

Barriers to Implementation:

• Complexity (multiple elements to coordinate)
• Cost (some interventions expensive - NPWT, laminar flow)
• Cultural resistance (changing established practices)
• Time pressure (pre-operative preparation time)
• Lack of ownership (who is responsible for bundle compliance)

Success requires institutional commitment, leadership support, dedicated resources, and sustained effort. Bundles are most effective when integrated into routine workflow rather than additional tasks.

Global Epidemiology

• SSI is among the most common healthcare-associated infections worldwide and the leading hospital-acquired infection in many low- and middle-income settings, where the pooled cumulative incidence is around 5.6 per 100 surgical procedures, markedly higher than in high-income countries (Allegranzi et al., Lancet 2011).
• Reported orthopaedic SSI rates rise sharply with wound class and implant burden: roughly 1-3% for clean elective arthroplasty/fusion, rising to 15-40% for dirty/infected wounds.
• Meticillin resistance is a global driver of practice variation: in developing-country surveillance, around half of S. aureus isolates were meticillin-resistant, shaping decolonisation and glycopeptide-prophylaxis policy.

Major Guidelines, Side by Side

Core recommendations converge internationally, with the main differences being emphasis (e.g. weight-based vancomycin, glucose targets) rather than direction.

Registry & Surveillance Evidence

National joint registries quantify deep infection as a leading cause of revision and benchmark performance, while national surveillance networks track SSI rates and prophylaxis compliance.

Global Practice Variation

• High- vs limited-resource settings: higher baseline SSI rates in low-resource settings reflect supply, sterilisation and surveillance constraints; WHO guidance is deliberately implementable without high-cost infrastructure (e.g. relies on bundles rather than laminar flow).
• Laminar-flow ventilation: retained in many high-income arthroplasty theatres but not universally mandated; benefit is debated once modern bundles are in place.
• MRSA decolonisation: universal vs targeted screening differs by local MRSA prevalence and funding; not uniformly reimbursed.
• Intrawound vancomycin (spine): widely adopted despite predominantly observational evidence, with regional differences driven by stewardship policy.

Surgical site infection prevention in orthopaedic surgery requires a comprehensive, evidence-based approach spanning the entire perioperative period. Success depends on implementing multiple interventions in a bundled fashion, as no single measure is sufficient.

Pre-operatively, focus on modifiable risk factors: glycemic control (HbA1c less than 7%, perioperative glucose less than 10 mmol/L), smoking cessation (minimum 4 weeks), nutritional optimization, MRSA screening and decolonization, and pre-operative chlorhexidine bathing. These interventions can reduce SSI risk by 40-70% in high-risk patients.

Intra-operatively, meticulous attention to antibiotic timing (30-60 minutes before incision), skin preparation (chlorhexidine-alcohol preferred), appropriate hair removal (clipping not shaving), maintenance of normothermia, operating room discipline, and surgical technique are critical. Each element has Level 1 evidence supporting efficacy.

Post-operatively, appropriate wound care, continued glucose monitoring, early drain removal if used, and comprehensive patient education ensure continued infection prevention and early detection if infection occurs.

Special considerations for implant surgery include enhanced protocols such as laminar flow operating rooms, antibiotic-loaded cement for cemented arthroplasty, and intrawound vancomycin for spinal instrumentation. Open fractures require early antibiotics (within 1 hour), timely debridement, and appropriate soft tissue management.

For exam preparation, focus on evidence levels for interventions, Australian guidelines (eTG), timing of antibiotic prophylaxis, skin preparation agents, and comprehensive bundle approaches. Understanding both the evidence and practical implementation demonstrates clinical competence and commitment to patient safety.