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Joint aspiration: The dry tap

Authors
W Neal Roberts, Jr, MD
Curtis W Hayes, MD
Section Editor
Daniel E Furst, MD
Deputy Editor
Monica Ramirez Curtis, MD, MPH

INTRODUCTION

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 to the potential causes of a dry tap as well as to the need for advanced imaging.

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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Literature review current through: Nov 2017. | This topic last updated: Sep 13, 2017.
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