DRY TAPS AND WHAT TO DO ABOUT THEM - A PICTORIAL ESSAY ON FAILED ARTHROCENTESIS OF THE KNEE

PURPOSE: To determine and illustrate the causes of unproductive arthro centesis of the knee. PATIENTS AND METHODS: Consecutive patients were studied who had inflammatory (rheumatoid or psoriatic) arthritis affec ting the knees and experienced unproductive arthrocentesis during a ra ndomized, controlled trial. Magnetic resonance imaging (MRI) was used, supplemented first by intravenous gadolinium contrast and subsequentl y by manual mixing of the diffused contrast to outline the furthest po ssible penetration of contrast within the joint cavity. RESULTS: In 4 out of 5 patients studied, failed arthrocentesis was due to combinatio ns of inspirated joint fluid too viscous to be withdrawn or to mix wit h contrast, adipose tissue, and lipoma arborescens (thickened synovium with fat replacement). One MRI exam was normal. More free synovial fl uid was imaged on the lateral side. CONCLUSIONS: Failure to aspirate s ynovial fluid from the knee is explicable in anatomic terms; in partic ular, fluid viscosity and lipoma arborescens play a role in chronic ef fusions. Although surface anatomic landmarks for knee arthrocentesis m ay be more visible medially, the lateral approach is more likely to yi eld fluid for synovial analysis in difficult cases. Internal medicine trainees should be taught the lateral approach.