by Marie Westby, B.Sc., P.T.
Now that you have a new knee or hip and can move around with considerably less pain, you may ask yourself, What’s next? Should you park this high-tech joint replacement in the garage and bring it out only for leisurely Sunday drives? Or should you take it out for a test drive and see how well it performs? How many miles can you put on your new joint? What kinds of activities can you engage in without damaging it — can you go walking, for example, or play tennis, or ride your bicycle? Read further to learn the answers to questions like these, commonly asked by people who have had total joint replacement surgery.
More than half a million Americans undergo total hip replacement (THR) or total knee replacement (TKR) surgery each year. This number is growing as the population ages. Also, as surgical techniques and materials improve, younger individuals are beginning to seek out these procedures. This has led to a steady increase in the number of surgeries performed on people under the age of 55. (To learn more about knee and hip replacements, see our November-December 2004 and July-August 2005 issues.)
Osteoarthritis (OA) is the primary cause of knee and hip joint damage that leads to joint replacement surgery. Other factors include injuries, congenital problems, and rheumatoid arthritis (RA). Whatever the cause, joint damage brings pain and stiffness that leads people to cut back on their everyday activities, including sports and recreation. But cutting back on physical activity is a catch-22. Although it means that you place less stress on the damaged joint, it also means that you begin to lose muscle strength and bulk, increase the rate of bone loss, reduce proprioception (that is, your ability to sense the position and movement of your joints and limbs), and alter reflex responses in the muscles around the joint. These changes may lead to increased joint stress and pain, accelerated joint damage, and a greater risk of falls. Both research findings and common sense suggest that remaining active and maintaining good muscle strength and flexibility before surgery may mean a speedier recovery, less postoperative pain, and greater overall satisfaction with the surgery.
There is less agreement regarding how active to be after surgery. And many, if not most, individuals want to resume the recreational and sporting activities that they had to give up before surgery. A 2003 Australian survey of 216 people, carried out between one and two years after a hip replacement, found that the percentage of people participating in sports after surgery actually increased to 91% from a presurgery level of 87%. The activities weren’t necessarily the same, however. The most common activities after surgery were walking and water exercises; many people gave up golfing, tennis, and jogging.
In a study published in The Journal of Rheumatology in July 2004, researchers asked people to recall how active they had been since knee replacement surgery. The study, led by Dina Jones, Ph.D., found that people were able to engage in low-impact activities after knee replacement surgery without harming the new joint. The most commonly reported leisure activities were gardening and yard work (65%), walking for exercise (62%), and swimming (46%). What is really needed is a long-term study that does not rely on people’s memories but instead follows them for several years after their hip or knee replacement and monitors how being physically active affects a joint replacement. This has not yet been done. Orthopedic surgeons and researchers agree that regular exercise is important for all age groups. Exercise has numerous health benefits, such as reducing the risks of obesity, high blood pressure, heart disease, Type 2 diabetes, and osteoporosis. Resuming an active lifestyle after hip and knee surgery is also linked to improvements in cardiovascular fitness. The American Academy of Orthopaedic Surgeons suggests that exercise is important both in the recovery process and in the years after surgery. What we’re not yet sure of is just how active you should be and which specific exercises you should be doing.
We do know that there is a limit to how much load and stress you can put on a new joint. Joint loads are the forces to which joints are subjected. One example is compressive force (weight pressing down on the joint). Another is shear force (sliding movement of the joint from side to side). Greater loads will increase the wear and tear on parts of your new joint — most notably on any parts made of polyethylene. Polyethylene is a very durable and rigid plastic, but polyethylene particles can break away from the implant and cause a body tissue response that leads to bone destruction. Newer implant materials such as metal-on-metal and ceramic-on-ceramic surfaces may result in less particle debris. However, this is still being studied. (Studies released in 2012 found that many metal-on-metal hip implants have a higher than acceptable failure rate and an FDA panel has since discouraged their use.) Whichever type of material is used in your replacement joint, the total amount of particles produced by wear and tear depends on at least two factors: (1) the number of steps you take (your activity level), and (2) the amount of load you put on the new joint. Number of steps and load affect wear differently. Double the number of steps, and you double the amount of wear. Just a small increase in load, however, can cause a large increase in wear. Factors like this explain why in a hip replacement with a plastic cup component, the cup wears anywhere from less than 0.1 millimeters (around 3/1000 of an inch) a year to 0.3 millimeters (around 1/100 of an inch) a year.
Last Reviewed on August 22, 2012
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