This year, more than 400,000 knee replacements will be done in the U.S. That’s a lot of bionic parts. “A study in the Journal of Bone & Joint Surgery in 2004 predicted that number to be 3.4 million by 2030,” says Dr. Matthew Collard of Orthopedic Specialists. Among the suspected culprits responsible are the increases in obesity and in sedentary lifestyles. In addition, today’s emphasis on exercise means joints can be overused.
Genetics can also play a role, as can previous knee injuries like cartilage damage that makes osteoarthritis more likely. “A total knee replacement is indicated when non-surgical treatments don’t adequately control pain,” Collard notes. “Medication and less invasive surgical procedures are tried first; a total knee replacement is elective and a quality of life issue. You decide with your surgeon when the pain is too much or activities of daily living are too curtailed.”
For select patients, he says, a partial knee replacement may be an option. The knee has three compartments: inside, outside and behind the patella (kneecap). Partial replacement involves one of those compartments. The most common compartment to replace is the inside, but eventually, all roads lead to a total knee replacement.
Collard says patients should expect an average of 18 to 20 years longevity on a knee replacement, depending on activity. Successful outcomes are determined more by having a technically proficient surgeon than by the specific device used, he adds. He says additional innovations include having the plastic liners in the knees injected with vitamin E or some other antioxidant to increase longevity.
Dr. James Keeney of Washington University School of Medicine says that 10 percent of his total knee procedures are revisions, replacing a prosthesis that has worn out. “We have 20 to 30 years’ experience with knees, and the process has really changed within the last five to 10. Minimally invasive knee replacements do have smaller incisions than the open procedures, but it’s what we do under the skin that has changed.” He says in the past they cut into the quadriceps tendon. In minimally invasive surgery, the surgeon goes under the muscle so that almost 100 percent of the muscle stays attached to the kneecap. With the old technique, a patient couldn’t raise his leg for four days. Now most can do it immediately after surgery.
Another improvement has been making pain management more proactive. “We give pain and anti-inflammatory medication before surgery so they don’t wake up with as much pain; and during surgery we inject the knee with a combination of long-acting anesthetic and an anti-inflammatory,” Keeney explains. “We also use spinal or epidural anesthesia to block pain messages to the brain and in many cases avoid general anesthesia.”
Keeney says there are limitations to all knee implants that patients should know. “These are not sports knees,” he reminds. “We have to remove a critical ligament to do the surgery. Patients can do low-impact activity like ellipticals, aerobics, bicycling, skiing, doubles tennis or golf, anything that doesn’t involve a lot of pivoting. Extreme activity will wear out the knee replacement more quickly.”
Orthopedic surgeon Dr. Stephen Benz of Tesson Heights Orthopedics says knee replacements are at least 95 percent successful for pain relief, but they are never as good as the original equipment. “Longevity of knee replacements is better all the time, with 20-year survival at 90 percent, but I’m taking out bone and cartilage and replacing them with metal and plastic, so it won’t feel the same,” he says. “Partial knee replacements of one compartment feel more like your own knee. The partial procedure should also last 20 years, and if joint involvement progresses, a total knee replacement is still an option.”
He says research has shown that anti-inflammatories, cortisone shots and glucosamine are not good at keeping knee problems from progressing. The only thing that works consistently is keeping weight off. Benz will operate on very overweight people, but recovery is longer and complications from infection, blood clots and slowed healing are higher. He says his job is to improve quality of life. Patients also have a role. If they don’t lose excess weight, the stress will affect the new joint just like it did the original.