The synovial membrane is covered with nerve ends, which are very sensitive. Traumas, inflamation, and swelling can stimulate these nerve ends, causing pain and thus sending warnings to the body. This is a protective mechanism.
The above symptoms often occur intermittently, unpredictably, but persistently. They cause sufferers to lose productivity at work and to be unable to do things that they like to do, thus greatly diminishing their quality of life.