Knee Aspiration Landmarks
The recommended landmark for knee aspiration is the superolateral approach: insert the needle 1 cm above and 1 cm lateral to the superior lateral aspect of the patella at a 45-degree angle, advancing 1 to 1.5 inches into the joint space. 1
Technical Approach
Superolateral Portal (Most Common)
- Position the needle 1 cm superior and 1 cm lateral to the superolateral corner of the patella 1
- Insert at a 45-degree angle directed toward the intercondylar notch 1
- Advance the needle 1 to 1.5 inches until entering the joint space 1
- Apply local compression during aspiration to maximize fluid yield 1
Alternative Approaches
While the superolateral approach is most commonly described, no single approach portal has been proven superior in terms of accuracy or clinical outcomes 2. In experienced hands, the choice of portal (superolateral, superomedial, or lateral mid-patellar) is generally of no clinical consequence 2.
Image Guidance Considerations
When to Use Ultrasound Guidance
- Ultrasound guidance should be used when anatomic landmarks are difficult to palpate, particularly in obese patients where body habitus obscures the patella borders 3
- US guidance is appropriate to confirm suspected effusion and facilitate aspiration 4
- If initial blind aspiration yields a "dry tap," ultrasound-guided repeat aspiration should be performed, as a dry tap does not exclude the presence of joint fluid or infection 5
When to Use Fluoroscopy
- Fluoroscopy can facilitate aspiration for crystals or atypical/low-grade chronic infection 4
Pre-Procedure Requirements
Imaging Before Aspiration
- Plain radiographs of the knee should be obtained prior to joint aspiration to assess for underlying structural abnormalities 6
- Review radiographs before performing the aspiration 6
Antibiotic Timing
- Withhold antibiotics for at least 2 weeks before aspiration when infection is suspected to increase the likelihood of recovering an organism 5, 6
- Preaspiration antibiotic treatment can lead to false-negative aspirations 6
Common Pitfalls to Avoid
- A negative aspiration does not exclude infection—in 16% of patients, more than three aspirations were necessary to obtain positive culture 5
- Do not rely solely on the first attempt—large effusions can recur and may require repeat aspiration 1
- Avoid aspiration in patients currently on antibiotics for suspected infection 5
- Continuously refine and practice your preferred technique, as no approach portal is 100% accurate 2
- In patients where landmarks cannot be palpated, do not proceed blindly—use ultrasound guidance instead 3
Accuracy Enhancement
The accuracy of knee joint injection may be enhanced by using ultrasound guidance, particularly when anatomic landmarks are obscured or when initial attempts are unsuccessful 2. The knee joint is the most common and easiest joint to aspirate, but technical success depends on proper technique and appropriate use of imaging guidance when indicated 1, 7.