Patients and physicians may be reluctant to abandon widely used treatments that have been found to be ineffective. In 2002 and 2008 the New England Journal of Medicine published the results of clinical trials showing that arthroscopic debridement and lavage-surgical treatments to remove damaged tissue and debris-do not benefit patients with osteoarthritis of the knee. To determine whether the trials publication was associated with changes in practice patterns, we examined ambulatory surgery data from Florida and found that the number of debridement and lavage procedures per 100,000 adults declined 47 percent between 2001 and 2010. The reduction translates into national savings of $82-$138 million annually. These reductions may be offset by increases in the use of other procedures. The results indicate that clinical trials of widely used therapies can lead to cost-saving changes in practice patterns.