This study is a 24 week, placebo-controlled, parallel, double-blind, five-arm trial. The randomized treatment assignment will be stratified by participating study center and baseline pain score (mild, moderate to severe). In order to establish that the study is able to detect significant treatment effects for glucosamine, chondroitin sulfate and the combination of the two, celecoxib, already established to be effective, will also be compared to placebo. Patients will receive a rescue analgesic medication, acetaminophen, which they will be allowed to take for severe pain throughout the trial but not within 24 hours prior to a study visit.