Americans are swapping out joints at a record pace. More than a million people a year are getting a total joint replacement -- most typically an artificial hip or knee.
With an aging but still active population, the number of joint replacement surgeries is expected to grow dramatically, to some 4 million, in less than 20 years. More than half will be younger than 65.
Medical technology for the operations and the joints continues to improve, but there have been some problems. And the procedures are not cheap, typically running $20,000 and up for physician and hospital services alone, more for physical therapy and follow-up care.
Researchers have devoted much time and effort just in the past few years evaluating what works and doesn't in joint replacement, and those efforts underpin calls for better, more formal evaluation of candidates for the surgeries. While the procedures may certainly be life changing, they're technically not life saving.
(Disclaimer: The writer, mid-50s, had a total hip replacement with a metal and plastic joint less than two months ago -- a procedure delayed against medical advice for nearly a decade. Recovery so far has been remarkably rapid.)
There are a number of reasons that not everyone with a joint deteriorated by osteoarthritis or other causes can or should have it replaced. The joints wear out over time -- 15 years or so with average wear, sooner if the knees or hips support a lot of running or jumping.
While many people who get joint replacements hope they'll be able to be more active with less pain and greater range of motion, there's no guarantee they will become more fit or lose weight.
One recent analysis of a dozen studies that measured weight loss in patients after surgery found that 14 percent to 49 percent had lost weight; more patients had gained weight than lost. The review by researchers at San Diego State University and Kaiser Permanente was published online in September by the journal Critical Orthopaedics and Related Research.
In addition to the joints wearing out, the cement that holds the joints into existing bones of the leg, pelvis and other spots can crack and fail. Among the possible solutions is a new coating for implants that induces bone to quickly grow around the metal stem, eliminating the need for bone cement. A team at MIT is developing the thin films of growth factors.
Probably the biggest issue surrounding joint replacement is what materials are used in the joints -- options for hips have included metal into a plastic socket, metal into a metal socket, and ceramic-to-ceramic. Knee replacements generally use a mix of metal gliding on harder or softer plastics, with a great variety of designs attuned to function.
While metal-on-metal hip joints found favor with many surgeons who felt they were more durable and less likely to dislocate, concerns have arisen about the release of metals into surrounding tissue. Many surgeons hesitate to use ceramic implants on people who are big framed or overweight.
According to one recent study by doctors at the Hospital for Special Surgery in New York City, the structure of many failed metal implants may have caused them to rub and scratch the two parts, leading to material being released that caused reactions or infections in surrounding tissue. Another recent review of records involving more than 800,000 hip surgeries since the 1940s found no evidence that one type is more effective, but did find evidence of the risk posed by the metal-on-metal devices.
Scientists around the world are looking for better types of metal for implants, including those made with mini-structures that can more easily bend and bond with bone. Others are looking at cartilage and bone-growing techniques that might one day replace metal and plastic with lab grown tissue from our own stem cells.
Advances aside, total joint replacement may become harder to come by as employers and insurers try to set parameters of medical need for this and other elective surgeries.
A recent opinion piece in The New England Journal of Medicine by doctors at Weill Cornell Medical College in New York argued for using evidence-based criteria to prioritize patients most in need of hip and knee replacement, noting that people seeking the operations range from those trying to maintain active lifestyles to those who require surgery to perform the activities of daily life.
They noted "appropriateness criteria" could slow the increase in the number of surgeries. Studies in other countries have shown 60 percent to 80 percent of the operations were considered appropriate according to evidence-based criteria.