Early-onset arthritis may hit as many as one in every four young people who undergo anterior cruciate ligament (ACL) reconstruction surgeries, new research warns.

The arthritic pain emerges within 6 to 12 months post-surgery, according to Michigan State University (MSU) researchers.

Many of these cases occur in people under 40 and go unrecognized and untreated.

“We’re trying to change the narrative,” said study lead author Matthew Harkey, an assistant professor of kinesiology at MSU. “We see fairly young, active individuals experiencing extensive symptoms, but these symptoms are not interpreted by clinicians as something that may be related to osteoarthritis. Ignoring these symptoms might be setting them up to experience long-term decline and function.”

Tears to the ACL ligament within the knee are common, and often corrected with a surgery that replaces the ligament with a graft. Over 400,000 ACL reconstructions are performed in the United States annually, according to the National Institutes of Health.

In the new study, Harkey's team examined outcomes for 82 people, ages 13 to 35, who underwent ACL reconstructive surgeries.

Almost a quarter of the patients reported "persistent early arthritis symptoms from 6 to 12 months after knee surgery," according to a university news release.

In another Harkey-led study, data from 3,200 individuals supplied by the New Zealand ACL Registry showed that almost a third of patients developed arthritic pain within two years of their ACL surgery. That study will be presented soon at the Osteoarthritis Research Society International Conference in Austria.

Are all these young people recovering from an ACL surgery destined to get arthritis?

“It’s a bit complex — we can’t outright say arthritis is developing, but there’s a large group of patients whose symptoms linger long after surgery,” Harkey said in a university news release. “Often, clinicians assume that these post-operative symptoms will naturally improve as patients reengage with their usual activities. However, what we’re seeing suggests these symptoms persist and likely require a targeted approach to manage or improve them.”

Exercise and physical therapy could help boost strength and movement, even if arthritis does develop, Harkey's team said.

The findings were published recently in the Journal of Athletic Training.