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Nearly one-fifth of U.S. military officers with a history of traumatic knee injury had developed osteoarthritis (OA) visible on x-rays -- before age 30 in most cases, researchers found.

In a prospectively followed cohort of some 6,500 cadets at the nation's Army, Navy, and Air Force service academies, 117 were identified as having suffered knee injuries during their time there or previously, and of those, 22 (18.8%) had radiographic knee OA when examined a mean of 9 years later, according to Yvonne Golightly, PT, PhD, of the University of Nebraska Medical Center in Omaha, and colleagues.

Prevalence of knee OA as defined by , osteophyte scores, or joint space narrowing was 16 to 29 percentage points greater among these officers compared with other academy graduates without such injuries, the researchers reported in . The officers' ages at examination averaged 28 (SD 1.6).

Nine of those with knee injuries had already developed clinical symptoms of OA.

"The onset of [radiographic] OA at their young age and at the approximate halfway point of an anticipated 20-year military career is concerning, and highlights the need for primary injury prevention in this population and the secondary prevention of post-traumatic OA following injury," Golightly and colleagues concluded. "Approaches to monitor joint health, especially post-injury, are critical to identifying officers with early indicators of worsening functionality or joint pain, and subsequently to prevent and slow progression of OA and other debilitating joint conditions."

An association between knee injury and subsequent OA is not new, of course. Numerous studies have established that meniscal or ligament tears raise the risk for OA, and military trainees are obviously more prone than most people to such injuries. "The trauma of knee injury (with or without surgical repair) combined with sustained knee joint loading during their physically demanding careers likely predisposes military officers to post-traumatic OA," Golightly's group pointed out.

Nevertheless, they added, "the nature of the injury-OA association remains understudied, particularly in the military population," and even more so with regard to "the timing and progression of injury-mediated OA." The group noted that OA is the number one reason for disability discharge among service members.

For the current study, the researchers drew on a from 2004 to 2009, established to track risk factors for anterior cruciate ligament injury. A total of 6,452 were originally included, of whom 4,643 were still in contact with investigators during 2015-2017 for follow-up. Information was obtained from questionnaires completed at initial enrollment, and knee radiographs were conducted during study follow-up; 56 injuries had occurred prior to academy entry, 57 during training, and 24 following graduation.

About 200 service members with injuries were found; the 117 included in the final analysis were those consenting to and receiving follow-up exams. This group was matched to 143 cohort members with no record of knee injury and who also underwent the subsequent exams.

Some 38% of both groups were women (who were oversampled when making up the original cohort). Just over 80% were white, 4% were Black, and the rest were classified for race as "other" or unknown. OA was defined as having a Kellgren-Lawrence grade ≥2, osteophyte score ≥1, or joint space narrowing score ≥1. Both knees were affected in 25 of the knee-injured group, such that, among both groups, a total of 137 knees were injured and 383 were not.

Prior to the follow-up exams, six of the knee-injured group and one of the controls had been diagnosed with OA. That latter individual was the only one in the control group to have Kellgren-Lawrence scores or symptoms indicative of OA.

Most of the injured knees were actually free of objective evidence of OA at follow-up. About 56% had Kellgren-Lawrence scores of 0, 60% had an osteophyte score of 0, and 80% had no signs of joint space narrowing compared with 85%, 89%, and 96%, respectively, for uninjured knees.

On the other hand, that still left a substantial prevalence of OA in the injured knees. While none had advanced to the most severe stages, four showed Kellgren-Lawrence scores of 3, three had osteophyte scores of 2, and three had moderate joint space narrowing.

Golightly and colleagues also examined prevalence of OA features in relation to time since the original injury. Compared with uninjured knees, those experiencing damage before or during academy enrollment were significantly more likely to meet OA criteria, with differences of 12 to 32 percentage points (all P<0.02); but when the injury occurred after graduation, there was no significant difference in OA prevalence relative to uninjured knees.

The study came with a number of limitations, the investigators noted. The rigors of academy training and military service mean the results may not be generalizable to the population at large; also, the analysis was restricted to officers who remained in the military up to the time of follow-up, "who were presumably healthier than officers who were no longer serving." Furthermore, the follow-up (averaging 6 years after graduation) was not sufficient to fully explore the timing of OA development.

"Longer follow-up of participants may inform the progression from joint injury to structural changes to symptoms," Golightly and colleagues wrote.

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