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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- PJI is a biofilm infection; common pathogens are coagulase-negative staphylococci and S aureus
- Sinus tract communicating with prosthesis is diagnostic of PJI
- Evaluate with ESR/CRP, joint aspiration for synovial WBC/differential and culture; avoid superficial swabs
- Early postoperative or acute hematogenous PJI may be treated with debridement, antibiotics, and implant retention if implant stable
- Chronic PJI usually needs one-stage or two-stage exchange arthroplasty plus prolonged antibiotics
- Rifampin is important for susceptible staphylococcal PJI with retained hardware, but never use rifampin monotherapy
Overview
Prosthetic joint infection is infection involving a joint arthroplasty and adjacent tissue. Organisms adhere to hardware and form biofilm, making eradication difficult without surgery. Presentation may be acute with fever, erythema, drainage, and severe pain, or chronic with indolent pain and loosening. The diagnostic and management approach differs from native septic arthritis because hardware stability, symptom duration, organism, and surgical options determine therapy.
Epidemiology
PJI complicates a minority of hip and knee arthroplasties but causes substantial morbidity. Risk factors include prior joint surgery, early wound complications, diabetes, obesity, rheumatoid arthritis, immunosuppression, S aureus colonization, bacteremia, and revision arthroplasty. Early infections often involve S aureus, gram-negative rods, or polymicrobial flora; delayed indolent infections often involve coagulase-negative staphylococci or Cutibacterium acnes in shoulder arthroplasty.
Clinical Features
Symptoms
Persistent joint pain after arthroplasty, often the most common symptom
Early infection: fever, erythema, warmth, swelling, wound drainage, severe pain
Chronic infection: loosening, reduced function, subtle swelling, little or no fever
Acute hematogenous infection: sudden painful prosthetic joint after bacteremia or distant infection
Sinus tract or persistent drainage over prosthesis
Systemic toxicity or sepsis in virulent acute infection
Signs
Pain with range of motion and reduced function
Warmth, effusion, erythema, wound dehiscence, or purulent drainage
Sinus tract communicating with prosthesis is diagnostic
Instability or signs of mechanical loosening
Fever and hypotension are uncommon in chronic PJI but ominous when present
Investigations
First-line
ESR and CRPUseful screening tests; normal values reduce probability but do not fully exclude low-grade infection
Plain radiographsEvaluate loosening, osteolysis, fracture, hardware position; may be normal early
Joint aspirationSynovial WBC count, neutrophil percentage, Gram stain, aerobic/anaerobic cultures; key diagnostic test
Second-line
Multiple intraoperative tissue culturesObtain during revision/debridement; more reliable than superficial swabs
Alpha-defensin or leukocyte esteraseAdjunct synovial tests when diagnosis unclear
Blood culturesIf fever, acute hematogenous presentation, or S aureus suspected
Specialist
Advanced imagingNuclear medicine or MRI with metal artifact reduction may help when aspiration is nondiagnostic, but infection remains a microbiologic diagnosis
Orthopedic and infectious diseases consultationNeeded for all suspected PJI because surgical strategy and antibiotic plan are interdependent
1
Initial approach
- Do not start antibiotics before aspiration/cultures if patient is stable
- If septic or bacteremic, obtain cultures then start empiric therapy promptly
- Empiric therapy often covers MRSA and gram-negative rods until culture data return
- Assess implant stability, symptom duration, soft tissue envelope, organism, and surgical candidacy
2
Surgical strategies
- DAIR: debridement, antibiotics, and implant retention for early postoperative infection or acute hematogenous infection with stable implant and short symptom duration
- One-stage exchange: selected patients with known susceptible organism, good soft tissue, and adequate bone stock
- Two-stage exchange: common approach for chronic PJI in the United States
- Resection arthroplasty, arthrodesis, or amputation for non-reconstructable or refractory cases
3
Antibiotic therapy
- Culture-directed prolonged antibiotics are required after surgical intervention
- Staphylococcal PJI with retained hardware: rifampin-based combination therapy after bacteremia is controlled and wound stable
- Never use rifampin alone because resistance emerges rapidly
- Chronic suppressive oral antibiotics may be used when curative surgery is not possible
4
Prevention
- Optimize diabetes, weight, nutrition, and skin infection before arthroplasty
- Perioperative prophylaxis per institutional protocol; screen/decolonize S aureus in selected programs
Complications
- Implant loosening and failure: Biofilm infection leads to chronic inflammation and bone loss
- Recurrent infection: Especially with retained hardware or resistant organisms
- Bacteremia: Acute hematogenous infection can seed other sites
- Functional loss: Revision surgery, spacer placement, or arthrodesis can impair mobility
- Antibiotic toxicity: Long courses require monitoring for renal, hepatic, hematologic, and drug-interaction effects
USMLE Step 2 CK Exam Tips
- 1Sinus tract communicating with prosthesis = diagnostic of PJI
- 2Do not rely on superficial wound swabs; aspirate the joint for culture
- 3Biofilm explains why chronic PJI usually needs hardware exchange
- 4Early stable implant infection can sometimes be managed with DAIR
- 5Rifampin helps staphylococcal biofilm infection but must be combined with another active drug
- 6Chronic painless loosening after arthroplasty can still be infection
- 7S aureus bacteremia in a patient with prosthetic joint pain = acute hematogenous PJI concern
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