Joint aspiration: The dry tap
- W Neal Roberts, Jr, MD
W Neal Roberts, Jr, MD
- Chief of Rheumatology
- University of Lousiville
- Curtis W Hayes, MD
Curtis W Hayes, MD
- Professor of Radiology
- Virginia Commonwealth University
- Section Editor
- Daniel E Furst, MD
Daniel E Furst, MD
- Section Editor — Treatment Issues in Rheumatology
- Clinical professor, University of Washington, Seattle
- Clinical professor, University of Florence, Florence, Italy
- Professor of Rheumatology, University of California in Los Angeles (Emeritus)
- Director of Research, Pacific Arthritis Associates
In occasional patients, a joint that has obvious fluid on physical examination yields a “dry tap” during diagnostic arthrocentesis, even after the needle has been redirected and is clearly in the joint space. This problem comes up with surprising frequency with respect to the knee and also occurs with joints that are more difficult to tap, such as ankle and shoulder. The proper approach to a dry tap in an individual patient has to take into account, above all, the degree of suspicion of a septic joint. When joint fluid is necessary for diagnosis, consideration should be given both to the differential diagnosis of the causes of a dry tap and to a change in technique which this differential implies.
CAUSES OF A DRY TAP
There are three major explanations for a dry tap after extraarticular placement of the needle tip is excluded (table 1):
●Mistaken physical diagnosis
●Blockage of the bevel of the needle by plica, fat, or debris
●Very high viscosity fluid or true lipoma arborescens
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