Sometimes it's impossible to tell the serious from the not-so-serious medical conditions. With aging come age-related changes in the body. With the knee, joint cartilage such as the meniscus starts to wear out. Early signs of arthritis start to set in.
But most experts agree that early intervention can make a big difference in many kinds of problems. Don't wait to see your doctor. An X-ray may be all that's needed. In some cases an MRI is best. If conservative care doesn't improve your symptoms, then a second MRI may be needed.
Recently several studies have documented cases of spontaneous osteonecrosis in adults over age 60 who had some meniscus degeneration. Osteonecrosis is the death of bone. Spontaneous means it came on suddenly with no warning and no known cause. These are the kinds of problems you want to avoid by checking with your doctor sooner than later.