ACL tears are as common as sports headlines—think football player Tom Brady and golfer Tiger Woods. The anterior cruciate ligament (ACL) is one of four knee ligaments that connect bone to bone.  Two of them, including the ACL, form an X through the knee, controlling back and forth motion.

ACL tears are most common in young active people with otherwise healthy knees.  Of those who tear ACLs, about 50 percent develop osteoarthritis (OA) within 10 to 15 years. That means ACL tears offer a unique opportunity for researchers: A window into the process of osteoarthritis in healthy, young knees from the time of injury onward.

Such insight could fuel the discovery of new strategies and drug therapies that are better able to slow or stop the progression of osteoarthritis.  Researchers believe their work will also help them one day better determine who is at risk of developing OA.

“In general, when we’re talking about osteoarthritis, we’re talking about a 65-year-old patient,” says Scott Rodeo, MD, an orthopedic surgeon at the Hospital for Special Surgery in New York City and a co-principal investigator for a multicenter ACL study, also conducted at the Mayo Clinic and the University of California-San Francisco and funded by the Arthritis Foundation. “We have no idea when the OA began, and we don’t know if it involved trauma.  That makes it so hard to study. But we’re changing that by looking early at young patients who had normal knees.  We know the onset of trauma, and we can study early changes.”  

Post-traumatic Osteoarthritis

Researchers believe that post-traumatic osteoarthritis could be triggered by changes in the knee’s biomechanics--the movement of and forces on the knee, says Sharmila Majumdar, PhD, vice chair for research, professor and director of the Musculoskeletal and Quantitative Research Group at the University of California-San Francisco and a co-principal investigator for study: “Even after the ACL is repaired, the biomechanics are not restored.  And a release of biochemical markers initiate cartilage deterioration.  Bone injuries also occur during an ACL injury.  But it’s unclear whether they initiate responses that result in cartilage degeneration.”

It’s those mysteries that investigators plan to unravel.

Researchers will recruit 24 patients over two years between the ages of 18 to 50 who have torn their ACL within the past 14 days and who have otherwise healthy knees. Each patient will have a baseline physical exam and urine and blood tests, and a sample of fluid that lubricates the joint (synovial fluid) will be taken.   

If the patient has surgery to repair their torn ACL, researchers will also perform a synovial biopsy – the removal of some tissue lining the knee joint – six weeks later. All tests except the biopsy will be repeated at six months and then every year for five years.