When Jason Lalli tore his left anterior cruciate ligament at age 26, he thought he would be fine as soon as he had his knee repaired. As a soccer player who competed through college and then on recreational teams, he knew that ACL injuries could be debilitating but also that orthopedists could fix them.

He figured that he would miss a season, but that he could play and coach the game he loved for the rest of his life.

Four years later, his knee began to ache, and the pain became more constant over time, nagging almost “like a toothache,” he said. Within about another year, Lalli’s doctor did more work on the knee and gave him bad news: He had arthritis.

And, Lalli eventually learned, it was almost predictable.

Orthopedists have believed for years that torn tendons or ligaments put patients, no matter how young, at risk for arthritis. But quantifying the long-term risk has been difficult because most orthopedic patients are not studied for extended periods after their injuries.

Dr. Mininder Kocher, an orthopedics professor at Harvard Medical School, has reviewed the available data and determined that the chance of getting arthritis within a decade of tearing a tendon or a ligament in the knee is greater than 50 percent.

Lalli, now 39 and a resident of Canonsburg, Pa., is hobbled by knee pain. He gave up soccer. Then he had to give up running. He has tried swimming and cycling, but he said, “My heart is not in it.” Some days he can barely walk.

And he has no memory of any doctor warning him that he could get arthritis.

“It’s like a dirty little secret,” said Kocher, who is also associate director of the division of sports medicine at Boston Children’s Hospital. “It’s not that anyone is covering up. It’s just that it’s not well known.”

But as someone who spends his days repairing torn knee ligaments in teenagers, he is worried. He has written a paper, soon to be published, that says the number of ACL operations at 26 children’s hospitals in the United States has soared as more children and adolescents play sports that involve twisting the knee, like soccer and basketball, and often participate year-round.

“This is a major issue for me,” said Kocher. “If a 15-year-old gets arthritis in 10 years, knee replacement is not a great option at age 25.”

While knee injuries have received the most attention in research on arthritis risk, other joints are not immune, said Dr. Brett Owens, a professor of orthopedic surgery at Brown University Alpert Medical School. People who repeatedly sprain an ankle are at risk, he said. And up to 40 percent of those who dislocate a shoulder get arthritis within about 15 years, he said.