If you have arthritis and are facing hip or knee replacement surgery, you may be wondering how long the implant will last and if you'll need to replace the joint again some day. In this Health Alert, Johns Hopkins specialists answer this important question.

About 90-95% of hip implants last at least 10 years, and approximately 80-85% of knees last at least 20 years. Lab testing suggests that new implants could now last 20 to 25 years or longer. That's because older joint replacements made of plastic and polyethylene have now been replaced with those made of longer-lasting materials such as cross-linked polyethylene, a durable plastic; ceramic surfaces; or metal-to-metal ones that resemble ball bearings.

In the real world, how long a hip or knee implant lasts depends on how much use it gets. Although implants allow a return to active sports such as golf, biking, and swimming, they're not designed for impact sports like jogging or tennis. The trade-off may be that the hip or knee wears out sooner.

If you do need a second hip or knee implant, you will have what's called revision surgery. Sometimes people need a new hip or knee implant if the original plastic liner on the implant wears out, if the replacement loosens or breaks, or if they develop an infection.

Not all revisions require a replacement of every implant part. A simple revision is the replacement of a worn liner with a new one. A complex revision might involve grafting more bone onto the joint or dealing with an infection. In the case of infection, the replacement joint would have to be removed, and you would need intravenous antibiotics for six to eight weeks before the replacement could be reinserted.

Why do so many middle-aged women develop osteoarthritis? Scientists believe that declining estrogen levels may play a role.

Osteoarthritis is often called a wear-and-tear disease because it develops in joints after many years of use. Aging increases the risk of developing osteoarthritis, but it's not the sole cause. Scientists aren't sure exactly what causes the condition, but several factors play a role in its development. These include genetic predisposition, obesity, prior joint injuries, wear and tear on the joints due to repeated overuse or sports-related activities, muscle weakness, and nerve injury.

Now a study reported in the journal Arthritis and Rheumatism (Volume 54, page 2481) suggests that low estrogen levels are linked to osteoarthritis of the knee in middle-aged women.

Following up on findings from animal studies, researchers from the University of Michigan measured the estrogen levels of more than 800 premenopausal and perimenopausal women. Based on these results, they ranked the study participants into three groups according to their estrogen levels. The women had yearly x-rays of both knees and answered questions about knee pain, their general health, and various lifestyle factors.

After taking into account osteoarthritis risk factors such as body mass index, the researchers found that women with the lowest estrogen levels were nearly twice as likely to develop osteoarthritis over the next three years as were those with higher levels.

These findings may help explain why signs of osteoarthritis tend to appear when women are in their 40s, a time of fluctuating or declining estrogen levels. The relationship between estrogen and osteoarthritis isn’t clear. However, the hormone is believed to interfere with arachidonic acid, a substance in the body that is associated with pain and inflammation. The researchers suggest that a better understanding of estrogen’s apparent protective effect on the knee may lead to new approaches to osteoarthritis management.

Johns Hopkins Health Alerts | Arthritis | Osteoarthritis and Weight Loss

If you’re overweight and have osteoarthritis, you may wonder: How much weight do I have to lose before I see any benefits? Here’s the answer and it’s encouraging.

At Johns Hopkins we recently completed a five-year study that demonstrates that even small amounts of weight loss can result in significant improvements in osteoarthritis symptoms and functioning. We placed about 40 overweight and obese adults (average age 58) with knee osteoarthritis on a four-month program of lifestyle change. At the beginning of the study, participants with osteoarthritis experienced pain in one or both knees more than 50 percent of the time, causing difficulty in daily activities such as driving, climbing stairs, and getting in and out of bed.

The lifestyle changes we recommended for these osteoarthritis patients included moderate adjustments in both diet and daily exercise. The dietary changes emphasized principles of healthy eating (plenty of whole grains, fruits and vegetables) while limiting amounts of high calorie or nutritionally empty foods. The women were asked to eat between 1,400 to 1,600 calories a day; men were asked to stay within a range of 1,600 to 1,800 calories.

We also asked the study participants with osteoarthritis to gradually increase the number of steps they walked each day. They started at around 3,500 steps a day and gradually built up over the course of four months to around 10,000 steps a day, which was accumulated over the course of the day (10,000 steps is the equivalent of four to five miles, depending on stride length).

We were looking for a modest amount of weight loss. The average person with osteoarthritis in the program lost only about 15 pounds. However, with this modest weight loss, we saw significant improvements, both in the amount of osteoarthritis pain our subjects experienced and in their ability to function. Their reductions in pain averaged 41%; their improvements in functioning averaged over 50%. Again, that was from a weight loss of only 15 pounds. That degree of improvement exceeds the benefit we typically see in people who use even the strongest prescription anti-inflammatory medications.

We consider that degree of benefit from a relatively minor weight loss to be very encouraging news. Some of these people with osteoarthritis may still be heavy enough to be defined as obese, and yet they experienced impressive benefits. The anecdotal evidence from the trial was also very impressive. A number of osteoarthritis patients in the study were people who love to garden, but they’d essentially stopped gardening because it was just too painful and too difficult. After the weight loss, these osteoarthritis patients resumed gardening and they were thrilled. Did that mean they never had pain? No, it didn’t. After a day of gardening, they did experience some pain. However, their baseline level of pain was much lower, and they seemed much more able to tolerate the pain that they had in the past. I think, in part, this is because they felt so much better. They were recovering some of their zest for life.

Johns Hopkins Health Alerts | Arthritis | Osteoarthritis and Weight Loss

When it comes to the pain caused by knee osteoarthritis, there is a great need for an effective drug that doesn't cause dependency, because many patients either cannot tolerate, or don't obtain sufficient pain relief from traditional nonsteroidal anti-inflammatory medication. Finally, there may be a solution: Tanezumab.

According to Nancy E. Lane, M.D., Professor of Medicine and Rheumatology at the University of California at Davis Medical Center, and Director of their Center for Healthy Aging, a Phase II clinical trial of tanezumab has shown that treatment once every eight weeks significantly reduces pain in patients with moderate to severe knee osteoarthritis

Dr. Lane and her colleagues followed 444 men and women aged 40-78 who were unable to control their pain with non-steroid anti-inflammatory medication, such as ibuprofen or naproxen, or who were candidates for more invasive treatments such as total joint replacement.

The patients enrolled in this 16-week study were treated with either tanezumab or a placebo. Tanezumab is a humanized monoclonal antibody against nerve growth factor, or NGF. NGF stimulates the growth of sensory nerve cells and increases the body's response to pain. Tanezumab appears to block the pain signals.

Tanezumab was intravenously administered at 10, 25, 50, 100, or 200 µg/kg on days 1 and 56 of the study. The researchers measured effectiveness by evaluating knee pain with walking and patient assessment of response to the treatment as well as other outcome measures, including stiffness and physical function.

The results: Tanezumab significantly improved knee pain and the patients' overall assessments of their condition by 46% to 62% compared with 22% for those patients given placebo. At weeks 12 and 16, researchers noted a significant improvement in the secondary outcome measures, including pain, physical function, and stiffness. Within three days of the first dose of tanezumab, many patients in Dr. Lane's study experienced a greater-than-50% improvement in walking knee pain. At higher doses, there was a 70 to 80% drop in knee pain that continued over the next two months.

Based on these interesting study findings from Dr. Lane, it is clear that inhibition of NGF may provide a novel type of therapy to reduce the pain of osteoarthritis and possibly other pain conditions, including fibromyalgia, metastatic cancer pain, and degenerative disease pain.

Considering hip or knee replacement surgery? Because hip or knee replacement surgery is rarely an emergency, you have plenty of time to set your house in order before you go to the hospital. Here’s no-nonsense advice from Johns Hopkins doctors.

Hip or knee replacement surgery: Check Your Medical Coverage
The weeks before hip or knee replacement surgery are a good time to check your health insurance coverage to avoid any unpleasant surprises later on. This includes inquiring about or verifying coverage issues such as:

• Need for a second opinion on your hip or knee replacement surgery
• Hospital and health care providers' status as "in-network" or "preferred"
• Deductibles for hospital services
• Limits on length of stay
• Coverage for hospital rehabilitation services
• After-care services for your hip or knee replacement surgery, such as physical or occupational therapy (Ask whether the therapists must be from an approved list and how many visits or sessions are covered.)
• Equipment such as wheelchairs, walkers, and crutches, and whether they must be obtained from approved vendors
• Home health care coverage, what type, and for how long
• Coverage of follow-up visits with your physician

Hip or knee replacement surgery: Review the Procedure With Your Doctor
Ask your doctor to explain the hip or knee replacement procedure, the type of device being implanted, and what you should expect in terms of rehabilitation. You should discuss pain management, time on crutches or a walker, length of physical therapy, type of home assistance required, time off from work, restricted activities, and time until you can resume full activities.

Hip or knee replacement surgery: Prepare Your Home
Take a look at the rooms in your house to identify potential problem areas. To increase safety and convenience:

• Remove throw rugs and small items from the floor. Tape down electrical cords. Rearrange furniture to create wide pathways to accommodate a walker or crutches.
• Set up a bedroom downstairs.
• Place kitchenware and other frequently used items within arm’s reach. Buy a long-handled grabbing device.
• Consider installing handrails and grab bars in the bathroom and shower. A shower bench and elevated toilet seat are also helpful.
• Place a sturdy high-backed chair with arms in the room where you will spend most of your time.
• Set up a recovery center. Place a table and wastebasket near your chair. Include a phone, T.V. remote control, tissues, medications, water pitcher and glass, and reading material. Use a carpenter’s apron or shoulder bag to carry items around the house.
• Make or buy frozen casseroles, soups, and other easy-to-prepare foods.

Above all, don’t hesitate to ask friends and neighbors for help with groceries, transportation, or other tasks. With your new hip or knee, you’ll be able to return the favor down the road.