- A protocol-specified pain score for the target knee in response to Question 1 of the WOMAC pain index ("how much pain have you had [in the target knee, over the past 48 hours] when walking on a flat surface?") after washout of at least 5 half-lives of analgesic medication(s): acetaminophen, topical or oral NSAIDS, coxibs, opioids, and/or tramadol