The decision to have a joint replacement takes into consideration many factors. First, your age and general health are important. Previous treatment for arthritis is reviewed. There may be some conservative (nonoperative) care you haven't tried that can help before thinking about surgery.
X-rays are taken to view the condition of the joint. The surgeon looks at the joint space and bone density when advising you. During the physical exam, joint range of motion and strength are measured. Function, activities of daily living (ADLs), and quality of life are also part of the decision-making process.
If you've tried all the recommended steps in conservative care without success, then you may be a good candidate for surgery. Even without pain, function and quality of life may be improved enough by a joint replacement to make it worth doing.
Your orthopedic surgeon is the best one to advise you on all the treatment options and timing.