Achy knees bane of baby boomers.

• Position: Joints

Many people are staying active as they age. This is healthy. However, playing team sports, jogging, or performing other high impact activities that repeatedly pound, twist, and turn the knees can stress aging joints. Highly active, middle-aged patients may develop painful knees as a result of osteoarthritis (OA), which occurs when the cartilage lining on the ends of the bones gradually wears away. The American Academy of Orthopaedic Surgeons, Rosemont, Ill., outlines OA this way:

Symptoms. You may experience pain when standing or going up and down stairs. The knee may buckle and give way, lock in place, or become stiff and swollen.

Patients. Most individuals with OA of the knee are over age 55 and/or obese and/or have a family history of the condition. Younger, athletic people also may develop OA if a knee suffered a significant injury.

Diagnosis. See a physician or orthopedic surgeon for diagnosis and treatment. A doctor will consider your comprehensive medical history, perform a physical examination, and possibly order tests and imaging studies before recommending a course of action.

Increasingly, highly active patients in their 40s and 50s feel inspired by advertising and news reports about the success of knee replacement surgeries. First, however, they probably should attempt to change their lifestyles to extend the life of their natural knees. Doctors use a complex medical formula to determine whether total knee replacement is appropriate for a patient--considering age, activity demands, and other factors. Long-term results of joint replacement are less certain in younger patients, often requiring a revision of the original procedure.

For the middle-aged, the earlier a doctor diagnoses OA of the knee, the more likely conservative treatment may help. If OA is in its early stages, your physician may recommend low-impact activities and...