Maybe be due to underlying osteo arthritis...First of all Exercise is the cornerstone of treatment. The more you will mobilize the joint the better it will work. So try to have good tolerable exercise regularly. Next big step in treatment is Weight reduction. Don't burden the joint with your fat. The lesser the weigh the better the joint. So try to have healthy balanced diet with good exercise to reduce the suffering of joint. Rest and joint care is also very necessary as too much working will all to your problem. For the pain try warm bandages and local painkiller creams and sprays. If the pain is severe then medical therapy is recommended which includes drugs like Acetaminophen and NSAIDs these are the agents which actually reduce the pain and the swelling around the joint thus relieving symptoms. Along with medicines Physical therapies and Occupational therapies are very important...Consult nearest orthopedic surgeon they will do the needful.