Active duty U.S. military service members are doing more than serving the nation; they are providing researchers with an important window into how osteoarthritis, or OA, affects a young, active segment of the population.

A study, published online in the journal Arthritis & Rheumatism, found that active duty military personnel are at a significantly higher risk of developing OA than people in their age group in the general population.

“It’s pretty significant I think, because this group of people is obviously quite young,” says study author Kenneth Cameron, PhD, director of orthopaedic research at Keller Army Hospital in West Point, N.Y. “We think of OA as occurring in older individuals, but in a young, physically active population the burden can be quite high, and that’s a disease that will likely impact them their entire life.”

The researchers note that military personnel are exposed to repetitive joint-loading activities and tasks, and that osteoarthritis is a leading cause of disability and medical discharge among service members.

OA Risk Assessed for All Four Service Branches

For his study, Cameron and his team retrospectively analyzed records from the Defense Medical Surveillance System, or DMSS, of physician-diagnosed cases of OA among all four branches of active duty U.S. service members. Between 1999 and 2008, 108,266 cases were reported.

The researchers focused on so-called “incidence rates” (the number of new cases of osteoarthritis that occur) as opposed to “prevalence” (which reflects the number of existing cases). Cameron says it’s generally hard for researchers to identify new cases, but the military offers a rare opportunity to do so because of its population, tracking ability and resources.

More OA Among the Enlisted and Those Over 40 

Among the findings, osteoarthritis incidence rates in the military were 26 percent higher in the under-20 age group compared with the same age group in the general population. As expected, the incidence of OA rose as the groups increased in age – but in each age group, the gap between those in the military with osteoarthritis versus those in the general population with osteoarthritis grew larger too. Among those 40 years and older, the incidence of OA among service members was more than twice that of the general population.

Within the military population, after the researchers adjusted for age, race, branch of service and rank, they found women had a 20 percent higher incidence rate than men, and African-Americans were 15 percent more likely to be diagnosed with osteoarthritis than white people and 26 percent more likely than other racial groups.

Among the different branches, those in the Army had the highest risk, with an incidence rate 50 percent higher than those in the Navy (who had the lowest risk). Junior enlisted service members had a 67 percent higher OA incidence rate than junior officers.

Previous studies have suggested that some differences in osteoarthritis rates may be related to access to care, but Cameron says this study population doesn’t support that theory. “Everyone in the military has equal access to care, so it shouldn’t affect the rates in our study,” he says.

Military OA Study Benefits Civilians, Too

The U.S. Department of Defense has been giving out research grants to study various diseases since 1993 through the Congressionally Directed Medical Research Programs (CDMRP). Although this study didn’t receive CDMRP funding, it demonstrates how useful a partnership between Congress, the military and the medical community can be.

Laura Robbins, senior vice president of education and academic affairs at the Hospital for Special Surgery in New York City, sat on the panel that reviewed the first grant requests for osteoarthritis projects submitted to the Department of Defense last year. She says studying a military population with OA will benefit everyone with OA.

“We did not have a lot of research that looked at the longitudinal development of OA. Usually we see end-stage OA, when they need joint replacement,” says Robbins, who has a PhD in social welfare. “Studying young people in the military will let us look at OA in early stages and as it progresses. And the findings will have huge impact on disease mechanisms. It is very important and we are very glad this research is happening.

“The military is a perfect population to understand the wear and tear – because of their activity – on knee and hip joints. And if we can understand those mechanisms, it will help us understand the wear and tear and trauma on anyone’s joints,” she says. “That will be transferable to the average person in the general population so we can understand how to diagnose and treat it earlier.”

Results May Improve Long-Term OA Treatment 

Terry Moore, MD, director of rheumatology at St. Louis University in Missouri, an institution that treats a number of service members from a nearby Army and Air Force base, agrees. “Many people do not think that people get OA until they are in their 50s, 60s and 70s, and we know as rheumatologists that even early on we can see it,” Dr. Moore says. “These data emphasize the point that it’s not just an older person’s disease. Anyone with increased activity or trauma could develop it in their late 20s, 30s or 40s.”

Cameron says if people get the disease at a younger age, they will live longer with osteoarthritis, which could have long-term consequences. “The costs associated for treating OA that develops earlier in this and similarly active populations will also likely be significant over their lifetime. This is why it is critical to identify and develop effective primary and secondary prevention interventions, which is currently limited by our ability to identify incidence cases of OA earlier in the clinical course of the disease,” he says.