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Prosthetic Joint Infection (PJI) — Comprehensive Review

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1. Epidemiology & Overview

• Hip arthroplasty: 0.3–1.7%
• Knee arthroplasty: 0.8–1.9%
• Ankle and elbow replacement: 4–10% (highest risk)
• Risk in rheumatoid arthritis patients is 2–3× higher than the general arthroplasty population

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2. Pathogenesis & Microbiology

Biofilm: The Core Mechanism

• Dramatically increases resistance to antibiotics
• Resists phagocytosis by host immune cells
• Explains why cultures from infected joints are often difficult to grow
• Makes eradication nearly impossible without surgical debridement

Implanted foreign material creates a zone of local immunodeficiency around the device — the surrounding tissue cannot mount an effective immune response.

Routes of Infection

Microbiology

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3. Classification

Traditional Time-Based Classification (Goldman-Cecil / Harrison)

Therapeutic Classification (Harrison's — more clinically useful)

1. Acute hematogenous PJI: symptoms present for < 3 weeks; prosthesis well-fixed; may be candidate for DAIR
2. Early postinterventional PJI: manifests within 1 month after surgery; equivalent to acute
3. Chronic PJI: symptom duration > 3 weeks; biofilm established; implant exchange typically required

ICM-2018 Criteria (Miller's Review of Orthopaedics)

1. Presence of a draining sinus that communicates with the joint (absolute diagnosis)
2. Two positive cultures growing the same organism via standard culture methods

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4. Risk Factors

Patient-Level Factors

• Rheumatoid arthritis / SLE / psoriatic arthritis (autoimmune disease)
• Obesity (BMI ≥ 35)
• Diabetes mellitus (HbA1c > 7.0)
• Malnutrition (albumin < 3.5 g/dL)
• Advanced age (> 70 years)
• Smoking (cessation ≥ 30 days pre-op reduces risk)
• Immunosuppressive drugs — DMARDs, monoclonal antibody inhibitors, antirejection drugs
• Cancer

Surgical / Procedural Factors

• Prior superficial surgical site infection
• Prior infection of the same joint
• Previous surgery on the joint
• Prolonged operative time
• Simultaneous bilateral arthroplasty
• Requirement for blood transfusion / allogeneic blood transfusion
• Active infection elsewhere in the body (hematogenous seeding risk)

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5. Signs & Symptoms

Acute PJI (Early / Hematogenous)

• Joint pain — most universal symptom
• Erythema, warmth, and swelling over the joint
• Fever
• Poor wound healing / wound drainage
• Joint effusion
• Local inflammatory signs (more prominent at knee than hip)

Chronic / Delayed PJI

• Joint pain (often the only symptom — insidious onset)
• Implant loosening (mechanical feel)
• Joint effusion
• Occasional sinus tract draining through skin
• Absence of fever (low-virulence organisms like CoNS, C. acnes cause subclinical infection)
• Non-specific symptoms mimicking aseptic loosening

Key insight: Chronic PJI caused by low-virulence organisms presents with nothing more than chronic pain — requiring a high index of suspicion.

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6. Diagnostic Imaging & Tests

Laboratory (Serum)

Synovial Fluid Analysis (Joint Aspiration)

Imaging

Intraoperative

• At least 3, optimally 6 tissue samples for culture and histopathology
• Sonication of removed implant material followed by culture or molecular methods — detects organisms in biofilms that evade standard culture

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7. Imaging Gallery

Multi-modal imaging: PJI of the left hip

(a) AP X-ray: THA in situ with no obvious loosening on plain film. (b) Coronal T1 MRI: subfascial fluid collections around the prosthetic neck. (c) Coronal 18F-FDG-PET/MRI: markedly elevated metabolic activity around prosthesis neck and shaft. (d) Axial PET/MRI: intense FDG uptake in periprosthetic bone marrow (arrow) — intramedullary inflammation not visible on X-ray alone. This case illustrates how PJI can appear radiographically silent yet be metabolically active.

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Chronic PJI: osteolysis, loosening, and revision surgery

(A) Severe periprosthetic osteolysis with superior migration and tilting of the acetabular cup, cortical thinning at the proximal femur — infection-induced bone destruction. (B) Post-revision: long-stem revision prosthesis, antibiotic-impregnated calcium granules (beads) for local infection control, cerclage wires for femoral stabilization.

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Sinus tract, DAIR procedure, and biofilm visualization

(A) Large constrained cemented knee prosthesis. (B) Cutaneous sinus tract anterior to the knee — pathognomonic for PJI. (C) Intraoperative DAIR procedure setup. (D) Arthroscopic view showing organic biofilm adherent to the metallic prosthetic surface — direct visualization of the microbial pathology that makes PJI so difficult to eradicate.

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8. Effects & Systemic Impact

• Functional loss of the joint — pain, reduced mobility
• Implant loosening — may be indistinguishable from aseptic loosening clinically
• Bone destruction / osteolysis — especially in chronic infection
• Sinus tract formation — chronic draining wound
• Septicemia and sepsis — especially from virulent organisms (S. aureus)
• Mortality: 1-year mortality of 40–50% in PJI following hemiarthroplasty for hip fracture
• Repeated surgeries — significant psychological and financial burden
• Amputation — in severe, uncontrollable cases

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9. Treatment

Principles

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Surgical Options (4 curative approaches)

Option 1: DAIR — Debridement, Antibiotics & Implant Retention

Option 2: One-Stage Exchange

• Remove infected prosthesis + thorough debridement → immediate reimplantation in same operation
• Requires: identifiable pathogen with known antibiotic susceptibility, good soft tissue coverage, no sinus tract
• Most common in Europe for selected cases

Option 3: Two-Stage Exchange (Gold Standard in the USA)

• Stage 1: Remove all hardware + thorough debridement → place antibiotic-loaded cement spacer (PMMA) — articulated spacer preferred when soft tissues allow
• Interval: 6–12 weeks of targeted IV antibiotics
• Stage 2: Reimplantation once infection markers normalize and tissue cultures are negative
• For knee: medial gastrocnemius rotational flap is the main workhorse for soft tissue deficiencies (blood supply: medial sural artery; covers medial and anterior knee defects)

Option 4: Implant Removal Without Replacement (Resection Arthroplasty)

• Last resort for patients unfit for reimplantation
• Provides infection control at the cost of joint function
• Amputation reserved for life-threatening uncontrolled infection

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Antibiotic Therapy

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10. DAIR — Debridement, Antibiotics & Implant Retention: Complete Explanation

What is DAIR?

1. Surgical debridement — aggressive removal of all infected/necrotic tissue, synovium, and fibrinous material
2. Exchange of modular components — polyethylene liner, femoral head, and any other removable parts are replaced (reduces biofilm burden on modifiable surfaces)
3. Retention of well-fixed implants — the stem and cup/tray remain if stable
4. Wound irrigation — copious pulsed lavage
5. Targeted antibiotic therapy — prolonged oral/IV antibiotics including biofilm-active agents (rifampin for staphylococci, fluoroquinolones for gram-negatives)

Arthroscopic lavage alone is NOT acceptable as DAIR — open arthrotomy with full access is required.

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Conditions Required for DAIR Success (>80% cure rate)

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Why Timing Matters (Biofilm Maturation)

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DAIR in Acute Hematogenous PJI (ICM-2018 & Harrison's)

• DAIR is preferred if symptoms < 3 weeks
• S. aureus is the most common organism
• Exchange of modular parts is mandatory
• Follow with rifampin-combination oral therapy for 3–6 months

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SEM Evidence of DAIR Efficacy

Scanning electron microscopy at 1500× showing implant surfaces at 28 days: (left) uninfected — smooth surface; (middle) infected without treatment — dense biofilm covering 90% of surface; (right) DAIR-treated — biofilm significantly reduced to 61% with visible metal surface beneath. Statistical analysis (p=0.0011) confirms DAIR reduces biofilm burden, though it cannot completely eliminate it — explaining why antibiotic continuation is essential.

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DAIR vs. Two-Stage Exchange: Decision Algorithm

PJI confirmed
    │
    ├── Acute (symptoms < 3 weeks) + stable implant + susceptible organism?
    │       ↓ YES → DAIR
    │
    ├── Chronic (symptoms > 3 weeks) OR loose implant?
    │       ↓ → Two-stage exchange
    │
    ├── Poor surgical candidate / severe comorbidity?
    │       ↓ → Lifelong suppressive antibiotics
    │
    └── Uncontrollable / life-threatening?
            ↓ → Resection arthroplasty / amputation

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11. Prevention

Perioperative Measures

Patient Optimization (Pre-op)

Secondary Prevention (Dental / Procedural)

• Patients with total joint replacements undergoing invasive dental or urological procedures — previously routine prophylaxis is now not universally recommended (AAOS/ADA 2012 guidelines cautious; individualized decision-making for high-risk patients)
• Prompt treatment of remote infections (skin, urinary tract, dental) to prevent hematogenous seeding
• Educate patients to report new-onset joint pain promptly during bacteremic illnesses

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12. Recent Consensus — ICM 2018 (International Consensus Meeting)

Key ICM-2018 Contributions:

• Sinus tract communicating with the joint
• Two positive cultures, same organism

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Summary Table

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• Harrison's Principles of Internal Medicine 22E (2025) — Chapter 136
• Goldman-Cecil Medicine International Edition — Chapter 255
• Miller's Review of Orthopaedics, 9th Edition
• ICM-2018 Consensus Guidelines; EBJIS 2021 Definition (McNally et al., Bone Joint J)

Timeline of PJI Consensus Guidelines

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What the 2025 Consensus Updates

• Molecular diagnostics (next-generation sequencing, 16S rRNA PCR) formalized for culture-negative PJI
• D-dimer and fibrinogen as additional serum biomarkers gaining stronger evidence
• Alpha-defensin lateral flow assay (point-of-care) validated more broadly
• DAIR protocol refinements — stronger emphasis on organism identity before committing to retention (specifically, DAIR is discouraged for resistant organisms like MRSA in some frameworks)
• One-stage exchange gaining more traction globally as equivalent to two-stage in select patients
• Fungal and mycobacterial PJI given dedicated pathways
• Antibiotic-coated implants and local delivery systems (calcium sulfate beads, DAIR-adjunct irrigation) gaining evidence

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What Hasn't Changed

• Biofilm is the core problem
• Acute vs. chronic distinction drives surgical decision-making
• Rifampin combinations remain the backbone for staphylococcal PJI
• Two-stage exchange remains the benchmark for chronic infection in North America

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DAA (Direct Anterior Approach) for Total Hip Replacement (THR)

10-Mark Exam Answer

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1. Introduction & Historical Background

• Originally described by Carl Hueter (1881) and later refined by Smith-Petersen (1917)
• Reintroduced for THA in the 1990s–2000s (Judet brothers, then Matta in the USA)
• Today one of the three major approaches for THR alongside posterolateral and direct lateral (Hardinge)

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2. Patient Positioning

• Both legs fully extended, neutral rotation
• Traction table allows limb manipulation (extension, external rotation, adduction) to deliver the femur into the wound without flipping the patient
• Fluoroscopy/image intensifier used intraoperatively to confirm cup/stem positioning
• No lateral positioning required — this is a major advantage for bilateral cases

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3. Skin Incision & Surface Landmarks

Key Landmarks:

• ASIS (Anterior Superior Iliac Spine) — primary landmark
• Greater Trochanter (GT) tip
• Tensor Fasciae Latae (TFL) muscle belly

Incision:

• Begins 2–3 cm lateral and distal to the ASIS
• Directed toward the fibular head (distally)
• Length: 7–10 cm in standard minimally invasive DAA
• Runs along the anterior border of the TFL

Exam point: The incision starts 2–3 cm distal and lateral to the ASIS and angles toward the fibular head.

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4. The Surgical Interval — Hueter Interval

Superficial Interval:

The fascial incision is made over the TFL muscle belly, more laterally placed — this protects the LFCN which runs medially.

Deep Interval:

True internervous plane: femoral nerve (medially) vs. superior gluteal nerve (laterally) — no muscle is cut.

Diagram to Draw in Exam:

        ASIS
         |
    _____|_____
   |           |
SARTORIUS    TFL ← fascial incision here
(med, fem.n) (lat, sup.glut.n)
         |
    HUETER INTERVAL
         |
  RECTUS FEMORIS  |  GLUTEUS MEDIUS
  (med, fem.n)    |  (lat, sup.glut.n)
         |
    HIP CAPSULE
         |
  FEMORAL HEAD & NECK

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5. Steps of the Operation

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6. Neurovascular Structures at Risk

1. Lateral Femoral Cutaneous Nerve (LFCN) — Most Common Injury

• Exits pelvis 1–2 cm medial to ASIS under the lateral inguinal ligament
• Supplies anterolateral thigh sensation (greater trochanter to knee)
• Injury → Meralgia paresthetica (burning, numbness, dysesthesia anterolateral thigh)
• Prevention: fascial incision made more laterally over TFL belly, not the TFL-sartorius border
• Incidence: up to 15–40% transient; ~2–5% permanent

2. Ascending Branch of Lateral Circumflex Femoral Artery (LCFA)

• Crosses the deep surgical field
• Must be identified and ligated early to prevent significant haemorrhage

3. Femoral Nerve

• Lies medial to the field between iliacus and psoas
• At risk from aggressive medial retractor placement
• Deep retractors placed incorrectly along acetabulum can also injure the external iliac artery

4. Femoral Artery & Vein

• Lie medially in the femoral triangle
• Protected by avoiding excessive medial retraction

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7. Advantages of DAA

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8. Disadvantages & Limitations

Exam key: The most frequent complication specific to DAA is LFCN injury/meralgia paresthetica. The most serious technical error is femoral fracture during broaching.

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9. Comparison with Other Approaches — Table to Draw

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10. Specific Complications of DAA

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11. Diagram to Draw in Exam

ANTERIOR VIEW — DAA HUETER INTERVAL

            ASIS ●
             |
             |  ← Incision starts 2–3 cm
             |     distal & lateral to ASIS
    _________|_________
   |                   |
SARTORIUS          TFL (fascia incised
(retract MEDIALLY)   laterally over belly)
Femoral n.          Sup.gluteal n.
   |                   |
   |   HUETER          |
   |   INTERVAL        |
   |                   |
RECTUS FEMORIS    GLUTEUS MEDIUS
(retract MEDIALLY)  (retract LATERALLY)
Femoral n.          Sup.gluteal n.
   |                   |
   |___________________|
            |
     ANTERIOR HIP CAPSULE
     (T-shaped capsulotomy)
            |
     FEMORAL HEAD & NECK
     (neck osteotomy here)

LCFA ascending branch: ligate in deep field
LFCN: protect medially within sartorius fascia

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Summary — One-Line Points for 10 Marks

1. DAA = true internervous, intermuscular approach — no muscle detached
2. Hueter interval: superficially TFL (lateral) vs. sartorius (medial); deeply TFL/gluteus medius vs. rectus femoris
3. Nerve planes: superior gluteal nerve laterally, femoral nerve medially
4. Patient positioned supine; traction table recommended
5. Incision: 2–3 cm distal and lateral to ASIS, angled toward fibular head
6. LCFA ascending branch must be ligated early in deep dissection
7. Most common complication: LFCN injury → meralgia paresthetica
8. Biggest technical risk: femoral fracture during broaching (tight proximal femur access)
9. Advantages: no hip precautions, lowest dislocation rate, immediate weight-bearing, better component positioning under fluoroscopy
10. Disadvantages: steep learning curve, poor femoral access, not suitable for revision, difficulty in obese patients

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• Rockwood & Green's Fractures in Adults, 10th Edition 2025 — Chapter 52
• Miller's Review of Orthopaedics, 9th Edition
• Imaging Anatomy: Bones, Joints, Vessels and Nerves