Knee Effusion After a Fall: Diagnosis, Drainage (Arthrocentesis) & Aftercare

A swollen knee after trauma often indicates hemarthrosis (blood in joint) or inflammatory effusion. Prompt evaluation determines if drainage is needed.

When to See a Doctor

• Rapid swelling (within hours) → likely hemarthrosis (ACL tear, fracture, vascular injury)
• Inability to bear weight
• Deformity, severe pain, locking
• Signs of infection: fever, redness, heat

Arthrocentesis (Joint Aspiration)

• Procedure: Sterile needle insertion (typically lateral mid-patellar or suprapatellar) under local anesthetic; fluid withdrawn with syringe.
• Duration: 5–15 minutes in office/clinic.
• Fluid Analysis: Gross appearance (bloody, serosanguineous, purulent) → send for cell count, crystals, Gram stain, culture.
• Therapeutic Benefit: Relieves pressure/pain; diagnostic value.

Post-Procedure Care

• Compressive dressing / knee sleeve for 24–48 hrs.
• Ice, elevation, relative rest 24 hrs.
• Weight-bearing as tolerated (crutches if painful).
• Monitor for recurrence (re-accumulation), infection signs.
• Follow-up for fluid analysis results & imaging (X-ray, MRI) as indicated.

Underlying Causes Requiring Specific Treatment

• ACL/PCL/meniscus tear → may need surgery
• Fracture (tibial plateau, femoral condyle, patella) → immobilization or ORIF
• Septic arthritis → urgent irrigation & IV antibiotics
• Gout/pseudogout → crystal-specific meds
• Osteoarthritis flare → conservative management

Do not ignore a traumatic knee effusion. Accurate diagnosis guides definitive treatment.