Ten thousand steps a day. That’s how far you must walk to meet government guidelines for physical activity to improve health. But if, like millions of people, you find walking painful or you fear your joints might buckle beneath you, each step might as well be a mile.

Your knees and hips are your largest joints. They support your body’s weight and they must work in close coordination to provide the mobility most people take for granted until injury, arthritis, or other problems interfere.

Joint replacement may be the answer

Depending on the cause of your pain, the solution might be a set of exercises designed to strengthen and stretch the muscles that support the joint, taking some of the stress off the joint itself. Minor surgery may also help. For many people, knee and hip problems become so intractable that the best solution is to replace a worn-out knee or hip with a mechanical joint. In the United States in 2003, there were 451,000 knee replacement and 364,000 hip replacement procedures performed. The average age at which a person has such surgery is 65 to 70.

Physically, your knees and hips are closely interdependent, located as they are at either end of the thighbone. This proximity means the angle of your hip affects the pressure on your knee. A hip disorder may cause knee pain, and knee disorders can aggravate hip problems.

People live longer than they used to, so joints need to stay strong and healthy through those additional years. But both knees and hips are subject to repetitive trauma — wear and tear — as you age, and you can traumatize them further if you increase your physical activity suddenly.

Advanced techniques make surgery easier

Medical care has changed in recent years. Doctors used to follow surgery by immobilizing the joint with a plaster cast. Weeks of immobility caused the muscles to weaken and shorten, resulting in long-lasting stiffness and poor function. Today, you can wake up from surgery with your knee already being gently bent and straightened by a machine. In addition, knee and hip replacements have freed thousands of patients from life in a wheelchair or on crutches.

Surgical techniques have also advanced. More surgery is performed through tiny incisions using an arthroscope, often on an outpatient basis. Pain relief has moved away from mind-clouding narcotics toward pain relievers that tackle the twin problems of pain and inflammation.

And finally, prevention has moved to center stage, alongside surgical repair and rehabilitation. More strength training added to your daily exercise routine helps support the joints and protect them from injury.