What is the recommended treatment for a stitch abscess following total knee replacement in an adult patient with no reported allergies?

Treatment of Stitch Abscess Following Total Knee Replacement

For a stitch abscess after total knee replacement, perform incision and drainage with aggressive debridement, obtain cultures, and initiate empiric IV antibiotics targeting staphylococci (cefazolin 2g IV every 8 hours or vancomycin 15 mg/kg IV every 12 hours if MRSA suspected), then tailor therapy based on culture results for 2-6 weeks. 1

Initial Assessment and Diagnosis

Clinical Evaluation

• Examine for signs of superficial versus deep infection: superficial stitch abscesses present with localized erythema, warmth, and fluctuance at the suture site, while deep prosthetic joint infection (PJI) manifests with persistent pain (especially at rest or night), joint effusion, and systemic symptoms 1
• Obtain inflammatory markers immediately: ESR and CRP are essential—when both are negative, deep infection is unlikely; CRP >13.5 mg/L has 73-91% sensitivity for PJI 1
• Recognize that peripheral white blood cell counts are typically normal even with prosthetic infection, limiting their diagnostic value 1

Imaging and Aspiration

• Order plain radiographs of the knee as the initial imaging study to evaluate for early loosening or osteolysis that would suggest deep infection rather than superficial abscess 1
• Perform joint aspiration if there is any concern for deep infection (pain persisting >6 months, elevated inflammatory markers, or radiographic abnormalities), as this is one of the most useful diagnostic tools alongside CRP 1

Surgical Management

Superficial Stitch Abscess (Isolated to Wound)

• Perform incision and drainage with removal of any involved sutures and debride all necrotic or infected tissue 2
• Send tissue and fluid for aerobic, anaerobic, and fungal cultures before initiating antibiotics whenever possible 1
• Consider this a potential harbinger of deeper infection: stitch abscesses can communicate with the joint space, especially if infection tracks along screw tracts in non-cemented prostheses 3

If Deep Infection Cannot Be Excluded

• Proceed with arthroscopic or open debridement with retention of prosthesis ONLY if: infection duration is <3 weeks, the prosthesis is stable, and there is no sinus tract 1
• Perform aggressive synovectomy and exchange of modular components (polyethylene liner) during debridement 1
• Obtain multiple intraoperative cultures (minimum 3-5 samples) from different sites within the joint 1

Antimicrobial Therapy

Empiric Antibiotic Selection

• Initiate cefazolin 2g IV every 8 hours as first-line empiric therapy for suspected staphylococcal infection in patients without beta-lactam allergy 1
• Use vancomycin 15 mg/kg IV every 12 hours if: patient has beta-lactam allergy, known MRSA colonization, or recent hospitalization in a unit with MRSA ecology 1
• Target organisms are: Staphylococcus aureus and coagulase-negative staphylococci (especially S. epidermidis), which account for the majority of TKA infections 1

Pathogen-Specific Therapy (After Culture Results)

For Oxacillin-Susceptible Staphylococci

• Administer nafcillin 1.5-2g IV every 4-6 hours OR cefazolin 1-2g IV every 8 hours for 2-6 weeks 1
• Add rifampin 300-450 mg orally twice daily if debridement with retention was performed, continuing rifampin with an oral companion drug for 3 months total for hip prostheses or 6 months for knee prostheses 1
• Preferred oral companion drugs with rifampin are: ciprofloxacin or levofloxacin (first choice), or co-trimoxazole, minocycline, or cephalexin as alternatives 1

For Oxacillin-Resistant Staphylococci (MRSA)

• Continue vancomycin 15 mg/kg IV every 12 hours for 2-6 weeks 1
• Alternative agents include: daptomycin 6 mg/kg IV every 24 hours or linezolid 600 mg PO/IV every 12 hours 1
• Add rifampin combination therapy as described above if debridement with retention was performed 1

Duration of Therapy

• Administer IV antibiotics for 2-6 weeks depending on organism virulence, extent of infection, and surgical approach 1
• If debridement with retention was performed, follow IV therapy with rifampin plus oral companion drug for total duration of 3 months (hip) or 6 months (knee) 1
• Monitor clinically and with laboratory tests (weekly CBC, CMP, CRP) for efficacy and toxicity throughout treatment 1

Critical Decision Points

When to Suspect Deep Prosthetic Infection

• Any stitch abscess occurring >3 months postoperatively should raise high suspicion for deep infection 1
• Pain at rest or night pain is characteristic of infection rather than mechanical issues 1
• Superficial surgical site infection is a risk factor for subsequent deep PJI 1

When Simple Drainage Is Insufficient

• If infection persists after initial drainage and antibiotics, or if the prosthesis is loose, proceed to two-stage reimplantation which has 91% success rate for infection eradication at long-term follow-up 4
• Two-stage exchange involves: complete removal of prosthesis and cement, placement of antibiotic-impregnated spacer, 6-8 weeks of IV antibiotics, then reimplantation once infection markers normalize 2, 4

Common Pitfalls to Avoid

• Do not dismiss a stitch abscess as purely superficial without evaluating for deep infection: obtain inflammatory markers and consider joint aspiration if any red flags present 1
• Do not use rifampin monotherapy: it must always be combined with another agent to prevent rapid resistance development 1
• Do not delay surgical intervention: early aggressive debridement within 3 weeks of symptom onset offers the best chance for prosthesis retention 1
• Do not forget to check for atypical organisms: while rare, non-tuberculous mycobacteria like M. abscessus can cause PJI and require prolonged combination therapy with prosthesis removal 5