Do I need to undergo knee aspiration?

Knee Aspiration: Indications and Recommendations

Knee aspiration is indicated only when there is suspicion of infection, crystal arthropathy, or a painful effusion that limits function, not as a routine procedure for chronic knee pain. 1

Indications for Knee Aspiration

Knee aspiration should be performed in the following specific scenarios:

1. Suspected infection:

   • When there are clinical signs of infection (fever, night pain, rest pain) 2
   • When inflammatory markers (ESR, CRP) are elevated 1
   • For patients with prosthetic knee joints when infection is suspected 1

2. Diagnostic purposes:

   • Unexplained joint effusion 3
   • Suspected crystal arthropathy (gout, pseudogout) 3
   • To distinguish between mechanical loosening and infection in prosthetic knees 1, 4

3. Therapeutic purposes:

   • Relief of a large, painful effusion limiting function 3
   • Prior to corticosteroid injection for inflammatory conditions 5

When Aspiration is NOT Indicated

• Routine evaluation of osteoarthritis without significant effusion 1
• Evaluation of osteochondritis dissecans, loose bodies, or history of cartilage repair 1
• Chronic knee pain without effusion 1
• When overlying soft tissue infection is present (contraindication) 3

Special Considerations for Prosthetic Knees

For patients with total knee arthroplasty:

• Aspiration has excellent diagnostic value with sensitivity, specificity, and accuracy of 100% for detecting infection in prosthetic knees 4
• If infection is suspected, aspiration should be performed after being off antibiotics for at least 2 weeks 1
• Multiple samples may be needed - in 16% of cases, more than three aspirations were necessary to obtain a positive culture 1
• Synovial fluid should be evaluated with:
  • Gram stain (limited sensitivity but high specificity)
  • Cell count and differential (>1700 cells/μL or >65% neutrophils suggests infection)
  • Aerobic and anaerobic cultures 1, 2

Clinical Effectiveness

• Aspiration provides only temporary improvement in symptoms for traumatic and non-traumatic knee effusions, with benefits lasting approximately one week 6
• Early re-accumulation of fluid often occurs 6
• However, aspiration can provide immediate clinical relief and is valuable for establishing diagnosis in effusions of unknown origin 6

Technique

• Aspiration should be performed using sterile technique 2
• Fluoroscopic or ultrasound guidance may improve accuracy, especially for prosthetic knees 1
• Common approach: insertion of needle 1 cm above and 1 cm lateral to the superior lateral aspect of the patella at a 45-degree angle 3

Conclusion

Knee aspiration is a valuable diagnostic and therapeutic tool but should be used selectively based on specific clinical indications rather than as a routine procedure for all knee pain. The decision to aspirate should be guided by the presence of effusion, suspicion of infection or crystal disease, or need for symptomatic relief of a large, painful effusion.