Can Diagnostic and Therapeutic Arthrocentesis Be Successfully Performed in the Flexed Knee?

Sabeen Yaqub, MD; Wilmer L. Sibbitt, Jr, MD; Philip A. Band, PhD; James F. Bennett, MD; N. Suzanne Emil, MD; Monthida Fangtham, MD; Roderick A. Fields, MD; William A. Hayward, PhD; Scarlett K. Kettwich, MS; Luis P. Roldan, BS; Arthur D. Bankhurst, MD


J Clin Rheumatol. 2018;24(6):295-301. 

In This Article

Abstract and Introduction


Background/Objective: The objective of this study was to determine whether the extended or flexed knee positioning was superior for arthrocentesis and whether the flexed knee positioning could be improved by mechanical compression.

Methods: Fifty-five clinically effusive knees underwent arthrocentesis in a quality improvement intervention: 20 consecutive knees in the extended knee position using the superolateral approach, followed by 35 consecutive knees in the flexed knee position with and without an external compression brace placed on the suprapatellar bursa. Arthrocentesis success and fluid yield in milliliters were measured.

Results: Fluid yield for the extended knee was greater (191% greater) than the flexed knee (extended knee, 16.9 ± 15.7 mL; flexed knee, 5.8 ± 6.3 mL; P < 0.007). Successful diagnostic arthrocentesis (≥2 mL) was 95% (19/20) in the extended knee and 77% (27/35) in the flexed knee (P = 0.08). After mechanical compression was applied to the suprapatellar bursa and patellofemoral joint of the flexed knee, fluid yields were essentially identical (extended knee, 16.9 ± 15.7 mL; flexed knee, 16.7 ± 11.3 mL; P = 0.73), as were successful diagnostic arthrocentesis (≥2 mL) (extended knee 95% vs. flexed knee 100%, P = 0.12).

Conclusions: The extended knee superolateral approach is superior to the flexed knee for conventional arthrocentesis; however, the extended knee positioning and flexed knee positioning have identical arthrocentesis success when mechanical compression is applied to the superior knee. This new flexed knee technique for arthrocentesis is a useful alternative for patients who are in wheelchairs, have flexion contractures, cannot be supine, or cannot otherwise extend their knee.


A number of anatomic landmark palpation-guided approaches are used to aspirate and inject the knee including the extended knee lateral or medial midpatellar and parapatellar approaches and the flexed knee lateral and medial anterior approaches.[1–22] However, for arthrocentesis, the extended knee superolateral approach where the needle is introduced into the lateral recess of the suprapatellar bursa and/or into the patellofemoral joint has been shown to be most successful and productive for arthrocentesis due to natural pooling of synovial fluid into the lateral suprapatellar bursa and patellofemoral joint.[8–25] Although the extended leg superolateral approach is highly accurate and most successful for arthrocentesis, a modified arthrocentesis technique that permits the patient to remain in the sitting position with a flexed knee yet provides similar arthrocentesis success and synovial fluid return as the extended knee would be of clinical utility in patients who have flexion contractures of the knee, are in wheelchairs, cannot recline, or cannot extend their knee for any reason.[3,8–25]

Recently, Bhavsar et al.[26] have demonstrated that mechanical compression of the knee reduces the chance of needlestick by removing the operator's hands from the puncture site and improves arthrocentesis success by shifting fluid anatomically to a portal where it can be accessed. We hypothesized that mechanical compression of suprapatellar bursa and patellofemoral joint of the flexed knee would remove the hands from potential needlestick and would also shift pooled synovial fluid from the superior knee (suprapatellar bursa and patellofemoral joint) to the inferior knee (synovial reflections of the cruciate ligaments and femoral condyles) where the fluid could be accessed by a needle.[26,27] Thus, the patient could remain seated with a flexed knee, and arthrocentesis could then be effectively performed using the same standard flexed knee anterolateral portal often used for injection.