What is the initial management and workup for a prepatellar abscess?

Management of Prepatellar Abscess: Workup and Treatment

The primary management of a prepatellar abscess is surgical incision and drainage, with timing based on the presence and severity of sepsis, followed by appropriate antibiotic therapy. 1

Initial Workup

Clinical Assessment

• Evaluate for:
  • Fever, tachycardia, tachypnea, or abnormal white blood cell count (SIRS criteria) 2
  • Local signs: erythema, warmth, fluctuance, tenderness over the prepatellar area
  • Predisposing factors: recent trauma, occupational hazards (kneeling), skin lesions, immunosuppression, steroid use, alcoholism 3

Diagnostic Studies

• Aspiration of fluid for:
  • Gram stain and culture (obtain before starting antibiotics) 2
  • Cell count and differential
• Blood cultures if systemic symptoms present (more common with prepatellar than olecranon abscesses) 3
• Imaging:
  • Ultrasound: first-line to confirm diagnosis, assess size and depth 1
  • CT or MRI: consider if deeper extension or complex presentation suspected

Treatment Algorithm

1. Surgical Management

• Incision and drainage is the cornerstone of treatment 1, 4
• Timing:
  • Emergent drainage for patients with sepsis, immunosuppression, diabetes, or extensive cellulitis 1
  • Within 24 hours for patients without these factors 1
• Technique:
  • Incision should be kept as close as possible to the abscess while providing adequate drainage 1
  • Complete drainage is essential to reduce recurrence risk (recurrence rates up to 44% with inadequate drainage) 1

2. Antibiotic Therapy

• Empiric coverage should target Staphylococcus aureus (accounts for 87.5% of cases) 3
• Initial regimen options:
  • Amoxicillin-clavulanic acid 875/125 mg PO every 12 hours 2
  • For MRSA coverage or penicillin allergy:
    • Trimethoprim-sulfamethoxazole 160-320/800-1600 mg PO q12h 2
    • Clindamycin 300-450 mg PO four times daily 2
    • Doxycycline 100 mg PO q12h (not for children <8 years or pregnant women) 2
• Duration: 7-10 days typically sufficient 2
• Adjust based on culture results

3. Post-Drainage Management

• Consider packing for wounds larger than 5 cm to prevent premature closure and reduce recurrence 4
• For severe infections, consider:
  • Percutaneous tube placement for suction-drainage and local antibiotic irrigation 5
  • Intravenous antibiotics until clinical improvement, then transition to oral therapy 2

4. Disposition

• Outpatient management appropriate for:
  • Small abscesses
  • Immunocompetent patients
  • No systemic signs of sepsis 1
• Inpatient management for:
  • Systemic illness/sepsis
  • Extensive cellulitis
  • Immunocompromised patients
  • Failed outpatient management

Follow-up

• Re-evaluation within 48-72 hours to assess healing progress 2
• Monitor for complications:
  • Spread of infection to adjacent structures
  • Systemic infection
  • Recurrence (particularly high with prepatellar abscesses)
  • Fistula formation 2

Special Considerations

• Prepatellar abscesses are associated with more aggressive clinical presentation, higher rates of fever (71%), leukocytosis (76%), cellulitis (59%), and positive blood cultures (25%) compared to olecranon abscesses 3
• Consider unusual pathogens in specific populations (e.g., Corynebacterium ulcerans in rural farmers) 6
• Routine imaging after resolution is not required unless there is recurrence or non-healing 1