A torn ACL (also known as the anterior cruciate ligament) is one of the most common knee injuries, with as many as 200,000 cases per year in the U.S. Young people under the age of 20 are at particular risk, in part because of participation in sports.
Despite the frequency of torn ACLs, many people don't know that the injury results in a significant risk of developing arthritis within 10 to . Around 70 to 80 percent of patients with a torn ACL will develop arthritis within that timeframe. Because most ACL injuries occur in young people, this means that arthritis could set in at a very early age. If a patient is 15 years old when she tears her ACL, for example, she could be struggling with arthritis by the age of 30.
Source: Medical Xpress