Pathophysiology & Risk Factors
Biofilm formation protects bacteria from antibiotics and immune response.
Common organisms: Staphylococcus aureus, S. epidermidis, and Gram-negatives.
Risk factors: prior surgery, obesity, diabetes, immunosuppression, long operative time, wound complications.
Host factors often outweigh surgical technique in determining infection risk.
Diagnosis
1.Clinical
Persistent pain, drainage, erythema, or early implant loosening.
Chronic PJI may lack systemic signs (fever often absent).
2. Laboratory
ESR >30 mm/h, CRP >10 mg/L → highly suggestive.
Normal ESR + CRP → infection unlikely.
3. Synovial Fluid
Aspiration before antibiotics.
Evaluate WBC count, %PMN, culture, and novel biomarkers (α-defensin, leukocyte esterase, synovial CRP).
≥2 positive cultures → diagnostic.
4. Imaging
X-ray: loosening or osteolysis (nonspecific).
MRI (metal-artifact reduction) → soft-tissue assessment.
PET-CT / Indium-labeled WBC scan for uncertain cases.
5. Intra-operative
≥5 tissue samples; >5 PMNs/HPF = infection.
Ultrasonication of explanted implants enhances microbial yield.
Treatment Strategies
1. Antibiotic Suppression
Reserved for unfit patients or non-surgical candidates.
Combination therapy (e.g., rifampicin + fluoroquinolone) may control low-grade infection.
2. DAIR (Debridement, Antibiotics, and Implant Retention)
Indication: acute infection (<3 weeks), stable implant, sensitive organism.
Success: 30–70%.
Early (<48 h) intervention improves eradication.
3. Resection Arthroplasty
Salvage in non-ambulatory or medically fragile patients.
High infection-control rate but poor function.
4. Single-Stage Exchange
Removal and reimplantation in one operation.
Indicated for known organism, healthy host, good bone stock.
Control rate: 80–90%.
5. Two-Stage Exchange (Gold Standard)
Step 1: remove all components, debridement, antibiotic spacer + 6 weeks IV therapy.
Step 2: reimplant after infection markers normalize.
Success: >90–95%.
Most reliable approach for chronic PJI.
Antibiotic-Loaded Cement & Spacers
Deliver high local antibiotic concentration.
Articulating spacers (e.g., PROSTALAC) maintain limb length and mobility while treating infection.
Recurrent or Resistant Infections
Options: repeat two-stage revision, chronic suppressive therapy, or salvage resection.
MRSA/VRE infections → rifampicin-based protocols remain effective.
Outcomes & Prognosis
Infection eradication: >90% achievable with early multidisciplinary care.
Function depends on timing, host status, and bone/soft-tissue preservation.
Key Pearls
Always rule out infection before any revision.
Combine serologic + synovial + intra-operative data for accurate diagnosis.
Early, coordinated management (orthopaedics + ID + microbiology) is vital.
Prevention: meticulous wound care, peri-op glucose control, skin optimization.
References
Parvizi J, et al. Clin Orthop Relat Res. 2021; 479: 985-99.
Tande AJ, Patel R. N Engl J Med. 2014; 370: 2451-62.
Zimmerli W, et al. Lancet. 2004; 364: 1539-54.
Osmon DR, et al. Infect Dis Clin North Am. 2020; 34: 57-75.