What are the appropriate management steps for an adult patient who underwent total knee replacement and now presents with dry skin and an open sore on the posterior leg with clear drainage, but no fever?

Management of Post-Total Knee Replacement Wound with Drainage

This patient requires urgent surgical consultation and joint aspiration to rule out prosthetic joint infection (PJI), as an open sore with drainage following total knee replacement is a potential surgical site infection that demands immediate evaluation regardless of the absence of fever. 1

Immediate Diagnostic Steps

Clinical Assessment Priority

• Pain characteristics are critical: Night pain or pain at rest strongly suggests infection, while pain only with weight-bearing suggests mechanical loosening 1, 2
• Absence of fever does not exclude infection: Chronic prosthetic joint infections frequently present with pain and wound drainage alone, without systemic signs like fever, erythema, or warmth 1, 2
• The "super dry skin" and "tight skin" described may indicate compromised wound healing or underlying infection 1

Laboratory Workup

• Obtain ESR and CRP immediately: These should be used together, achieving 93% sensitivity and 100% specificity when at least 2 of 3 tests are abnormal 2
• CRP has 73-91% sensitivity and 81-86% specificity for prosthetic knee infection using a cutoff of 13.5 mg/L 2
• Peripheral WBC count is not useful: Normal WBC does not exclude infection in prosthetic joint infections 1, 2

Imaging and Aspiration

• Obtain weight-bearing radiographs first: Look for signs of loosening, osteolysis, or component migration that may accompany infection 1, 2
• Proceed immediately with joint aspiration for synovial fluid analysis, culture, cell count, and differential 1, 2
• Withhold antibiotics for at least 2 weeks prior to aspiration if clinically feasible to avoid false-negative cultures 1, 2
• Synovial fluid leukocyte count >1700 cells/μL or >65% neutrophils suggests infection 1

Surgical Management Algorithm

If Superficial Surgical Site Infection (SSI) Confirmed

• Open the wound, evacuate infected material, and perform dressing changes until healing by secondary intention 1
• Antibiotics are unnecessary if: erythema <5 cm, temperature <38.5°C, WBC <12,000 cells/µL, and pulse <100 beats/minute 1
• Short course antibiotics (24-48 hours) indicated if: temperature >38.5°C, heart rate >110 beats/minute, or erythema extending >5 cm beyond wound margins 1

If Deep Prosthetic Joint Infection Suspected

• Debridement with retention strategy is appropriate only if: within 30 days of implantation OR <3 weeks of symptom onset, well-fixed prosthesis, no sinus tract, and antibiotic-sensitive organisms 1
• Two-stage exchange is the gold standard for established infections not meeting debridement criteria, with 82% success rate 1, 3
• At least 3-5 intraoperative tissue samples should be obtained for aerobic and anaerobic culture 1

Antibiotic Selection

For Clean Procedures (TKA)

• Staphylococcus aureus and coagulase-negative Staphylococcus (including S. epidermidis) are the most common organisms 1, 4, 3
• Empiric coverage should target Gram-positive organisms 1
• Consider MRSA coverage if patient has: long-stay care facility residence, hospitalization within 30 days, Charlson score >5, age ≥75 years, or prior antibiotic exposure 1

For Superficial SSI with Systemic Signs

• Initiate empiric broad-spectrum antibiotics if any systemic inflammatory response criteria present, signs of organ failure, or immunocompromised status 1

Critical Timing Considerations

Wound Healing Assessment

• Normal wound closure requires approximately 14 days after knee surgery 5, 6
• Before considering the wound healed, verify: no significant swelling, no erythema, no drainage, and clear evidence of healing 5, 6
• Patients with diabetes or on immunosuppressive medications may require longer healing times 6

Common Pitfalls to Avoid

• Do not delay aspiration: Clear drainage from an open sore post-TKA warrants immediate investigation, not observation 1, 2
• Do not rely on absence of fever: Chronic PJI commonly presents without systemic signs 1, 2
• Do not start empiric antibiotics before obtaining cultures unless the patient is septic or has systemic signs of infection 1
• Do not assume superficial infection: An open sore communicating with the joint space may represent deep infection requiring aggressive surgical management 1