For a study, researchers wanted to see if extended or flexed knee placement was better for arthrocentesis and if flexed knee positioning could be enhanced using mechanical compression. In a quality improvement intervention, 55 clinically effusive knees underwent arthrocentesis: 20 consecutive knees in the extended knee position using the superolateral approach, then 35 consecutive knees in the flexed knee position with and without an external compression brace placed on the suprapatellar bursa. The success of the arthrocentesis and the fluid production in milliliters were both assessed.
Fluid output was 191% higher in the extended knee than in the flexed knee (extended knee, 16.9 ± 15.7 mLL; flexed knee, 5.8 ± 6.3 mL; P<.007).In the extended knee, 95% (19/20) and 77% (27/35) of diagnostic arthrocentesis (≥22 mL) were successful (P=0.08). Fluid yields were essentially identical after mechanical compression was applied to the suprapatellar bursa and patellofemoral joint of the flexed knee (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).
When mechanical compression was applied to the superior knee, the extended knee superolateral approach was superior to the flexed knee for conventional arthrocentesis; however, when mechanical compression was applied to the superior knee, the extended knee and flexed knee positions had identical arthrocentesis success. This novel arthrocentesis approach with a flexed knee was a good option for patients who were in wheelchairs, have flexion contractures, can’t lie down, or can’t extend their knee in any other way.