What is the best treatment approach for an adult patient with no significant medical history who presents with a knee abscess and a buccal cheek abscess?

Treatment of Knee and Buccal Cheek Abscesses

Both abscesses require immediate incision and drainage as the definitive treatment, with antibiotics added only if systemic signs of infection are present. 1

Primary Treatment: Incision and Drainage

Drainage is non-negotiable and must be performed for both sites. 1, 2 The key principles include:

• Thoroughly evacuate all pus and probe the cavity to break up loculations at both the knee and buccal sites 1
• For larger abscesses (>5 cm), use multiple counter-incisions rather than one long incision to prevent step-off deformity and delayed healing 1, 2
• Cover with a dry sterile dressing after drainage; packing may cause unnecessary pain without improving outcomes 1, 2
• Never attempt needle aspiration, as it has only a 25% success rate overall and <10% with MRSA 1, 2

Imaging Guidance

• Ultrasound is highly accurate for confirming abscesses before drainage, with 96.7% sensitivity and 85.7% specificity 3
• US can also guide aspiration if needed and evaluate for loculations, foreign bodies, or vascular injury 3

Decision Algorithm for Antibiotics

Antibiotics are NOT routinely needed after adequate drainage if the patient lacks systemic signs of infection. 1, 2

When to AVOID Antibiotics (Simple Abscesses)

Skip antibiotics if ALL of the following are present: 1, 2

• Temperature <38.5°C
• Heart rate <100 beats/minute
• White blood cell count <12,000 cells/µL
• Minimal surrounding erythema (<5 cm from the abscess)

When to ADD Antibiotics (Complex Abscesses)

Add antibiotics if ANY of the following SIRS criteria are present: 1, 2

• Temperature >38°C or <36°C
• Tachycardia >90 beats/minute
• Tachypnea >24 breaths/minute
• WBC >12,000 or <4,000 cells/µL
• Immunocompromised status
• Incomplete source control after drainage

Antibiotic Selection by Location

For the Knee Abscess

Empiric coverage should target S. aureus (including MRSA) and streptococci: 1, 2

• First-line: Clindamycin 300-450 mg PO every 6-8 hours (or 600-900 mg IV every 8 hours if severe) 1
• Alternative: Vancomycin, daptomycin, or linezolid if SIRS is present or MRSA is suspected 2

For the Buccal Cheek Abscess

Broader coverage is needed due to mixed oral flora: 1, 4, 5

• Preferred: Clindamycin 600-900 mg IV every 6-8 hours (or 300-450 mg PO four times daily) 4
• Alternative combination: Cephalexin 500 mg every 6 hours PLUS metronidazole 500 mg every 8 hours 1
• Never use metronidazole alone, as it lacks activity against S. aureus and streptococci 1

The buccal location requires coverage for oral anaerobes in addition to staphylococci and streptococci. 4, 6, 5

Duration of Antibiotic Therapy

When antibiotics are indicated: 1, 2

• Standard duration: 5-7 days based on clinical response
• Immunocompromised patients: May require up to 7 days
• Re-evaluate at 7 days: Persistent infection beyond this timeframe warrants diagnostic re-evaluation with repeat imaging

Culture and Laboratory Testing

• Obtain Gram stain and culture of drained pus from both sites to guide antibiotic therapy 1, 2
• Consider blood cultures if bacteremia or sepsis is suspected 1
• Check CBC and CRP to assess infection severity; CRP >100 mg/L indicates more severe infection requiring increased surveillance 1
• Do not delay drainage while waiting for laboratory results 1

Critical Pitfalls to Avoid

• Never treat abscesses with antibiotics alone without drainage - studies show no benefit when drainage is incomplete 1, 2
• Do not underestimate buccal abscesses, as they can spread to deeper fascial planes and even descend to thoracic and abdominal compartments in severe cases 6, 7
• Avoid serratiopeptidase or similar proteolytic enzymes in the presence of abscess, as they can promote spread of infection 7
• For the buccal abscess, consider dental consultation to address any underlying odontogenic source 8, 6

Follow-Up and Monitoring

• Re-evaluate both sites at 48-72 hours to ensure clinical improvement 2, 4
• Persistent fever, bacteremia, or failure to improve indicates inadequate source control requiring repeat imaging and potential reoperation 1, 2
• Patients with ongoing signs of infection beyond 7 days warrant complete diagnostic re-evaluation 1, 2