Arthrocentesis Video
http://www.100md.com
《新英格兰医药杂志》
To the Editor: In the video of arthrocentesis of the knee by Thomsen et al. (May 11 issue),1 a folded towel is placed under the patient's knee to keep it semiflexed during the procedure. This intervention is likely to decrease the aspiration success rate in the case of small effusions.
Patients with large knee effusions feel more comfortable in semiflexion because it increases the volume capacity of the joint, therefore decreasing the intraarticular filling pressure.2 Full passive extension of the knee has the opposite effect. In large effusions, placing the knee in semiflexion, as shown in the video, will increase the patient's comfort without greatly affecting the procedure. But in small effusions, such as common noninflammatory cases of osteoarthritis, placing the knee in semiflexion will decrease the intraarticular filling pressure2 and could make the difference between a difficult and an easy knee arthrocentesis.3
Eddys Disla, M.D.
Cabrini Medical Center
New York, NY 10003
edisla@cabrininy.org
References
Thomsen TW, Shen S, Shaffer RW, Setnik GS. Arthrocentesis of the knee. N Engl J Med 2006;354:e19 (Web only). (Available at http://content.nejm.org/cgi/content/video_preview/354/19/e19.)
Alexander C, Caughey D, Withy S, Van Puymbroeck E, Munoz D. Relation between flexion angle and intraarticular pressure during active and passive movement of the normal knee. J Rheumatol 1996;23:889-895.
Wise C. Arthrocentesis and injection of joints and soft tissues. In: Harris ED Jr, ed. Kelley's textbook of rheumatology. 7th ed. Vol. 1. Philadelphia: Elsevier Saunders, 2005:704-5.
The authors reply: We agree with Disla that positioning the knee in full extension may be beneficial in certain patients. The patient in our video had a rather large effusion, and the procedure was performed without difficulty with the knee held in slight flexion.
We might add that although the medial approach to the knee joint was depicted in the video, entry from the lateral side may be chosen as well. The lateral approach may result in a successful aspiration if an attempt from the medial side is hindered by the presence of a medial plica or thick medial fat pad.1
Certainly, experienced clinicians will have their own preferences about how to perform any given medical procedure. Nonetheless, knowledge of alternative techniques (and the principles and anatomical underpinnings on which they are based) will often lead to successful results if initial difficulties in carrying out the procedure are encountered.
Todd W. Thomsen, M.D.
Gary S. Setnik, M.D.
Mount Auburn Hospital
Cambridge, MA 02238
tthomsen@mah.harvard.edu
References
Roberts WN, Hayes CW, Breitbach SA, Owen DS Jr. Dry taps and what to do about them: a pictorial essay on failed arthrocentesis of the knee. Am J Med 1996;100:461-464.
Patients with large knee effusions feel more comfortable in semiflexion because it increases the volume capacity of the joint, therefore decreasing the intraarticular filling pressure.2 Full passive extension of the knee has the opposite effect. In large effusions, placing the knee in semiflexion, as shown in the video, will increase the patient's comfort without greatly affecting the procedure. But in small effusions, such as common noninflammatory cases of osteoarthritis, placing the knee in semiflexion will decrease the intraarticular filling pressure2 and could make the difference between a difficult and an easy knee arthrocentesis.3
Eddys Disla, M.D.
Cabrini Medical Center
New York, NY 10003
edisla@cabrininy.org
References
Thomsen TW, Shen S, Shaffer RW, Setnik GS. Arthrocentesis of the knee. N Engl J Med 2006;354:e19 (Web only). (Available at http://content.nejm.org/cgi/content/video_preview/354/19/e19.)
Alexander C, Caughey D, Withy S, Van Puymbroeck E, Munoz D. Relation between flexion angle and intraarticular pressure during active and passive movement of the normal knee. J Rheumatol 1996;23:889-895.
Wise C. Arthrocentesis and injection of joints and soft tissues. In: Harris ED Jr, ed. Kelley's textbook of rheumatology. 7th ed. Vol. 1. Philadelphia: Elsevier Saunders, 2005:704-5.
The authors reply: We agree with Disla that positioning the knee in full extension may be beneficial in certain patients. The patient in our video had a rather large effusion, and the procedure was performed without difficulty with the knee held in slight flexion.
We might add that although the medial approach to the knee joint was depicted in the video, entry from the lateral side may be chosen as well. The lateral approach may result in a successful aspiration if an attempt from the medial side is hindered by the presence of a medial plica or thick medial fat pad.1
Certainly, experienced clinicians will have their own preferences about how to perform any given medical procedure. Nonetheless, knowledge of alternative techniques (and the principles and anatomical underpinnings on which they are based) will often lead to successful results if initial difficulties in carrying out the procedure are encountered.
Todd W. Thomsen, M.D.
Gary S. Setnik, M.D.
Mount Auburn Hospital
Cambridge, MA 02238
tthomsen@mah.harvard.edu
References
Roberts WN, Hayes CW, Breitbach SA, Owen DS Jr. Dry taps and what to do about them: a pictorial essay on failed arthrocentesis of the knee. Am J Med 1996;100:461-464.