Service members aged 40 years and older were at greater risk for all joint replacements overall and of each type specifically during the surveillance period (January 1, 2004, through December 31, 2014), according to a new report recently released in the May issue of the Medical Surveillance Monthly Report published by the Armed Forces Health Surveillance Center. However, during 2009–2014, incidence rates also increased in the following age groups: 30–34 years (45 percent); 35–39 years (107 percent); 40–44 years (130 percent); and 45 years and older (38 percent) (Figure 2).
During the surveillance period, overall incidence rates increased 10.5 percent during 2004–2009, and then 61.9 percent during 2009–2014 (Figure 1). Knee and hip joint replacements accounted for a majority of cases. In 2014, the rates of knee and hip replacements were identical (1.6 per 10,000 person-years [p-yrs]) and were the highest for each during the surveillance period. The report suggests that service members and their clinicians may be electing to have joint replacements at earlier ages amid improvements in surgical techniques and increased durability and longevity of prosthetic joints.
Service members are at risk for joint replacement for several reasons, the report noted. Military training and operational activities are often physically demanding, and sometimes traumatic. Some occupations are more stressful for bones and joints, and have been associated with higher frequencies of musculoskeletal disorders among service members during wartime and repeated deployments. In addition, recent increases in the incidence of overweight and obesity in service members can contribute to an increase in osteoarthritis and joint and back disorders among service members.8-14
“While more mid-career service members have had joint replacements, the procedures can prove beneficial to the health and readiness of the U.S. Armed Forces,” said Army Colonel Michael Bell, AFSHC’s director. “Each service member represents a precious resource for the Department of Defense. It takes years of training and experience to produce a seasoned NCO or Officer. If joint replacement allows service members to remain on duty longer and continue being valuable contributors to the military, then it will be a good thing for the U.S. Armed Forces. Additional studies are needed to determine the full impact of joint replacement on operational readiness.”
The report documents a total of 3,905 joint replacements among 3,805 active component members of the Army, Navy, Air Force, Marine Corps, and Coast Guard (an incidence rate of 2.43 per 10,000 person-years [p-yrs among service members]) during 2004–2014. Knee and hip joint replacements numbered 1,825 and 1,694, (with incidence rates of 1.16 and 1.08 per 10,000 p-yrs among service members, respectively).
Among the cohort of service members who had a joint replaced during 2004–2012 (n=2,902), 18.2 percent had retired; 5.2 percent had been medically disqualified from service; 6.3 percent had otherwise left service; and 70.3 percent were still in service one year after joint replacement (Table 3, Figure 3). By two years post-joint replacement, 30.2 percent had retired; 13.0 percent had been medically disqualified; 10.0 percent had otherwise left service; and 46.8 percent were still in service.
Of the services, the Army and Coast Guard had the highest overall rates of joint replacement (2.89 and 2.88 per 10,000 p-yrs, respectively) (Table 2). The Coast Guard had the highest rate of hip replacement (1.54 per 10,000 p-yrs) and the Army had the highest rate of knee replacement (1.46 per 10,000 p-yrs). The Army and Coast Guard had the highest rates of shoulder replacement (0.16 and 0.16 per 10,000 p-yrs, respectively). These findings may, in part, be accounted for by differences in age and occupational distributions between the services.
Among race/ethnicity groups, black, non-Hispanic service members had the highest rates of joint replacement overall and in the two largest joint replacement categories, hip and knee. Previous surveillance has documented that osteoarthritis, one of the leading causes of joint replacement, is diagnosed at higher rates among active component service members who are black, non-Hispanic.8 Among black, non-Hispanic service members aged 40 years or older, rates of osteoarthritis were 57 percent higher than rates among white, non-Hispanic counterparts. The age and occupational distribution is not uniform across ethnic groups in the military and may contribute to the findings presented above.
In civilian settings, rates of joint replacement are reportedly higher among white, non-Hispanics than among all other race/ethnicity groups.18 Differences in access to healthcare, which is at no cost to service members, may contribute to the relatively higher rates of joint replacement among black versus white, non-Hispanics in military versus civilian settings.
Click here to read the entire report. The MSMR is the flagship publication for the AFHSC, featuring articles on evidence-based estimates of the incidence, distribution, impact, and trends of illness in service members and associated populations.
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