10 Causes of Osteoarthritis You Might Not Know
It’s easy to chalk osteoarthritis (OA) up to one of the many joys of getting older—but you’d be seriously missing out on some important (and interesting!) info on what causes it in the first place. OA, the breakdown of joint tissue, is linked with aging, but certain factors increase your risk. “There are multiple causes of osteoarthritis,” says Dalit Ashany, M.D., a rheumatologist at the Hospital for Special Surgery, in New York City. “And a lot of research is being done to see if we can discover more.” Read on to learn the science behind 10 triggers of OA.
Though scientists are still investigating the role genetics plays in OA, research suggests it is a factor, says Dr. Ashany. Studies of identical twins suggest that genetics accounts for about 50% of OA risk—meaning if your parent or sibling has it, you’re definitely at increased risk. Researchers have even linked specific genes to OA, reports the National Institutes of Health, mostly those involved in forming and maintaining bone and cartilage. These faulty genes could impair the cartilage’s ability to heal, contributing to the risk of developing arthritis.
One of the biggest causes of OA is injury, says Brian Feeley, M.D., a professor of orthopedic surgery at University of California San Francisco and an orthopedic surgeon at UCSF Health. Because the cartilage or bone suffers damage, the joint may wear out more quickly. For knees, if you tear your anterior cruciate ligament (ACL), you’re four times as likely to develop knee OA in 10 years; and six times as likely if you injure your meniscus (shock-absorbing cartilage in your knee). Ankle OA can develop due to a fracture or severe strain. And shoulder arthritis can develop due to a rotator cuff tear, says Dr. Feeley.
While injury can increase the risk of developing arthritis at a younger age, most people are diagnosed after 55, says Dr. Feeley—perhaps because the cartilage between the bones naturally thins over time. Age can also impact muscle strength, balance, and “proprioception”—your awareness of your body’s positioning, says Dr. Ashany. That can mean less joint control and higher risk of injury—which (as we’ve already covered) increases your risk of developing OA.
Women are more likely than men to develop OA, though the reason is not clear. The risk is especially high during the menopausal years, leading some researchers to speculate it could be hormonal—but not a lot of evidence supports that, says Dr. Ashany, and it could have more to do with age than hormones. Or the reason could be simpler: Maybe women just go to the doctor more than men do, says Dr. Ashany.
Being Obese or Overweight
Having a body mass index of 25 or higher can raise the risk of knee OA three-fold. Carrying extra weight adds stress to your knees, hips, and spine—up to 60 pounds’ worth if you’re just 10 pounds overweight—accelerating wear-and-tear. In fact, for lower-extremity OA, says Dr. Feeley, “the most effective treatment is weight loss.” Even non-weight-bearing joints can be affected, though, because fat cells promote inflammation all over, including in and around your joints. This may be a reason why hand OA is twice as common in obese people as it is in leaner folks.
Sometimes OA boils down to the way your body is put together, says Dr. Ashany, which can impact the mechanics of how you move. Flat feet cause less stability and more joint stress, while a high arch is less mobile and can lead joints to jam. A hip condition called femoroacetabular impingement—where the ball doesn’t fit well into the socket—can damage cartilage. And scoliosis, or poor spinal alignment, can stress the spine. Those with a disparity in leg lengths—of as little as a half inch—may be more likely to develop knee OA, perhaps due to the uneven load.
Do your knees or elbows extend beyond straight? Can you touch your thumb to your forearm, or bend your fingers way back? “Some people are naturally born hyper flexible,” says Dr. Ashany. Kids call it being double-jointed; doctor’s call it hypermobility. Being able to move beyond a typical range of motion may mean you put more stress on the joint (which, again, may cause the joint to wear out more quickly), Dr. Ashany says. It can also mean your ligaments are more lax, increasing the risk of injury.
Work that demands repetitive motions can stress the joints and increase OA risk, says Ali Askari, M.D., division chief of rheumatology with University Hospitals in Cleveland. Research shows that people whose work requires heavy lifting, or excessive kneeling, squatting, or standing—like farming, mining, construction, or professional dancing—are more likely to develop OA. Can’t avoid it? Remember to take breaks! If OA symptoms are too much, talk to your employer about options, says Bill Robinson, M.D., chief of immunology and rheumatology at Stanford Medicine—he has one patient, a postal worker, who transitioned from a walking route to a desk job after developing knee OA.
A lack of exercise can lead to weakened muscles, says Dr. Askari, which may increase the risk of OA. In one study review of almost 6,000 participants, people with weak knee extensor muscles (which include the quadriceps, on the front of the thigh) were 65% more likely than stronger folks to develop symptoms of knee OA. Other studies suggest that strengthening your quads can decrease pain and improve physical function in those with knee OA. Joints can slip out of the right position without strong muscles to keep them in place, increasing injury risk. Keep your quads strong with strength exercises like squats, leg presses, and step-ups.
Metabolic Conditions, Inflammation, and Iron Overload
High blood pressure, heart disease, and diabetes have all been linked to OA. Makes sense since they all share risk factors like obesity, age, and inactivity. But some research suggests a deeper connection: High blood sugar from diabetes, for instance, can trigger the release of inflammatory proteins, as well as compounds (advanced glycation end products) that build up in and damage joints. OA can also be secondary to rheumatoid arthritis as well as hemochromatosis (“iron overload”)—both conditions can trigger degenerative changes in joint cartilage, leading to OA, Dr. Askari says.