Losing excess weight may help preserve knee cartilage in people who have or are at risk of knee osteoarthritis (OA), according to researchers at the University of California, San Francisco (UCSF), whose findings were recently published online in the journal Radiology. Knee cartilage is the rubbery, slick cap that covers the ends of the upper (femur) and lower (tibia) leg bones that make up the knee joint.
Their study also found that shedding extra pounds protected the menisci, the crescent-shaped cartilage pads that cushion the knee joint. Lead author Alexandra Gersing, MD, a postdoctoral scholar at UCSF School of Medicine, says this is especially important because a torn or damaged meniscus can speed up the degeneration of the knee joint overall.
“Weight loss seems to be protective for the knee joint and may slow the worsening of symptoms, such as pain and disability,” she says.
Although many studies have looked at the effects of excess weight on the knee, Dr. Gersing says this is the first to examine the long-term effect of weight loss on cartilage and the menisci.
For the study, Dr. Gersing and her colleagues analyzed data from a subgroup of 640 participants in the Osteoarthritis Initiative, a long-term, prospective study of healthy people, some with knee OA, others with risk factors for it and others without risk factors. The subgroup participants, who were all overweight or obese, were divided into three groups: those who over 48 months lost more than 10 percent of their body weight (considered substantial weight loss), those who lost 5 to 10 percent and those whose weight stayed the same.
Researchers compared the MRIs of the participants at the start of the study and four years later. They found that those with 5 to 10 percent weight loss had lower rates of cartilage degeneration than people who didn’t lose weight. But the greatest benefits were seen in the substantial weight loss group; they retained more healthy cartilage and had less menisci damage.
The researchers say there are several reasons for these findings. One is that being overweight increases the load on the knee joint, breaking down cartilage. Being overweight can also change a person’s gait, stressing the joint even more. Plus, fat cells themselves produce pro-inflammatory proteins that are now known to contribute to OA. So it makes sense that dropping excess pounds would have a positive effect on overall joint health.
The researchers acknowledge the study has some limitations. One of the most significant is that it doesn’t take into account how participants lost weight. Exercise, for example, significantly improves pain and function in arthritic joints. But in this study, there’s no way of knowing if the benefits to cartilage were due to exercise (which is good for the knee joint), weight loss or both.
Something else to keep in mind is that knee OA matters to people when it causes pain. But cartilage degeneration itself does not always cause pain. While it’s still OA, it’s classified as asymptomatic OA, meaning without symptoms. So from an individual’s point of view, changes picked up in the MRIs during the course of the study may not be important.
“The amount of pain depends on what structures of the knee are affected, to what extent they’re damaged and how this affects the surrounding knee joint structures,” Dr. Gersing explains. “Cartilage defects alone do not immediately cause pain, since cartilage doesn’t contain nociceptors [pain receptors].”
Heading Off Knee Damage
But that doesn’t mean these MRI changes aren’t important, because they may eventually lead to damage to the underlying bone, which is all the more reason for people with OA to shed extra weight before inflammation and degeneration become severe.
“I want to emphasize the importance of individualized therapy strategies and lifestyle interventions in order to prevent structural knee joint degeneration as early as possible in obese and overweight patients,” Dr. Gersing says. “It’s also important to control certain metabolic risk factors, such as high blood pressure and diabetes; our group has also shown that these risk factors are closely linked with obesity and the degeneration of knee joints.”
Geoffrey Westrich, MD, an orthopedic surgeon and research director of the Adult Reconstruction and Joint Replacement Service at Hospital for Special Surgery in New York City, says the UCSF study reinforces what surgeons have been telling patients for years – that extra weight is a major risk factor for arthritis of the knee joint.
“The end result for patients with progression of arthritis in the knee is total knee replacement surgery. While this surgery is clearly beneficial for pain relief, weight loss may slow the progression of osteoarthritis and delay [surgery] for obese and overweight patients,” he says. “In addition, studies show that surgery in obese patients has a greater likelihood of complications, so weight loss has the added benefit of making surgery safer, should it be necessary.”
Dr. Westrich, who was not involved in the study, says both exercise and weight loss are essential for joint health. He says people with knee OA should exercise as much as possible, after getting the go-ahead from their doctor.
“Start slowly and don’t be discouraged,” he says. Even 5 to 10 minutes on an exercise bicycle is a good start.”
Linda Rath for the Arthritis Foundation