There are some studies that show patients are at greater risk for knee re-injury after anterior cruciate ligament (ACL) tears if the damage isn't repaired. The most common injuries later are meniscus and joint cartilage tears.
If the joint cartilage is damaged, the bone underneath is unprotected. Wear and tear can cause damage to the bone. Painful arthritis can develop much later.
A recent study of over 6,000 adults confirmed these beliefs. Patients who didn't have an ACL repair and opted for conservative care were twice as likely to injure the meniscus later and 30 percent more likely to damage the joint cartilage.