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.
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.
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).
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.
From the *Division of Rheumatology, Department of Internal Medicine, and
†School of Medicine, University of New Mexico Health Sciences Center, Albuquerque, NM;
‡Department of Orthopaedic Surgery, Biochemistry & Molecular Pharmacology, NYU School of Medicine, New York, NY;
§The Department of Exercise and Sport Sciences, New Mexico Highlands University, Las Vegas, NM; and
∥School of Dentistry, Oregon Health & Science University, Portland, OR.
There was no internal or external support for this study.
All human and animal studies have been approved by the appropriate ethics committee and have therefore been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. All persons gave their informed consent prior to any procedures and prior to the inclusion in the study.
The authors declare no conflict of interest.
Correspondence: Wilmer L. Sibbitt, Jr, MD, Division of Rheumatology, Department of Internal Medicine, University of New Mexico Health Sciences Center, MSC 10 5550, 5th FL ACC, Albuquerque, NM 87131. E-mail: WSibbitt@salud.unm.edu.