(Reuters Health) – Young adults who have had knee injuries are much more likely than uninjured peers to develop arthritis in the knee by middle age, especially if they have broken bones or torn connective tissue, a recent study suggests.

Researchers followed almost 150,000 adults ages 25 to 34, including about 5,200 with a history of knee injuries, for almost two decades. Compared to people who never had knee injuries, those who did were nearly six times as likely to develop knee osteoarthritis during the first 11 years of follow-up, with more than triple the risk over the next eight years.

“Injuries that occur inside the knee joint, for example in the meniscus or cruciate ligament, may alter the biomechanical loading patterns in the knee,” said study leader Barbara Snoeker, of Lund University in Sweden.

“Such injuries may lead to an ‘imbalance’ in force transmissions inside the knee joint, consequently overloading the joint cartilage and leading to increased risk of developing osteoarthritis, compared to injuries that mainly affect the outside of the knee joint, such as contusions,” Snoeker said by email.

Osteoarthritis often affects the large weight-bearing joints and can eventually lead to the need for total joint replacement, the researchers note in the British Journal of Sports Medicine.

Known risk factors include being overweight, older, female or having a job that puts a lot of stress on the joints, the study team notes. While a history of knee injuries is also a known risk factor, research to date hasn’t offered a clear picture of whether certain types of injuries might be more likely to lead to osteoarthritis.

Two-thirds of the people in the study with knee injuries were male. After 19 years of follow-up, 422 people with knee injuries, or 11.3%, developed knee osteoarthritis. So did 2,854, or 4%, of people without knee injuries.

Most often, injuries involved multiple structures of the knee; this accounted for 21% of participant knee injuries. The second most common type of injury was cuts and contusions, at 18%, followed by cartilage or other tissue tears at 17%.

Cruciate ligament injuries, or damage to the tissue connecting the thighbone to the shinbone, were associated with a 19.6% greater risk of knee osteoarthritis, the study also found. Meniscal tears, or damage to cartilage connecting the same two bones, were associated with a 10.5% greater risk of osteoarthritis. Fractures of the shinbone where it meets the knee, or of the kneecap, were associated with a 6.6% greater risk.

Injuries involving multiple structures in the knee may have been underreported, leading researchers to underestimate the risk associated with these types of injuries, Jonas Bloch Thorlund, a professor of musculoskeletal health at the University of Southern Denmark, in Odense, who wasn’t involved in the study, said by email.

Another limitation is that researchers didn’t look at patient’s body mass index (BMI), so they couldn’t tell whether differences in weight might explain patients’ risk of osteoarthritis, said Dr. Kyle Hammond of the Emory Sports Medicine Center in Atlanta.

What happens after knee injuries can also influence the risk of osteoarthritis down the line, Hammond, who wasn’t involved in the study, said by email.

“Counseling a patient on how to safely and consistently return to a positive fitness program ensures that they will maintain flexibility and strength, as well as keeping their weight at their ideal body weight,” Hammond advised.

Rehab matters regardless of what other treatments patients receive, said Adam Culvenor, a sports and exercise medicine researcher at La Trobe University in Bundoora, Australia, who wasn’t involved in the study.

“Once these injuries occur, optimally managing them with an intense and progressive period of rehabilitation under the guidance of a physical therapist (irrespective of the decision to have surgery or not) to strengthen the muscles around the knee to facilitate a return to function and physical activity is likely to reduce the risk of osteoarthritis and persistent symptoms longer-term,” Culvenor said by email.

[Source: Reuters Health]