ACL injuries are more common in females but graft ruptures do not appear to be gender-based. Males and females are equally affected. About 10 percent of patients with an ACL reconstruction experience a graft rupture. It seems that age is the biggest factor. Patients younger than 21 years old are 10 times more likely to have a graft rupture.

Meniscectomy is also a risk factor for ACL graft rupture. Patients who have torn the meniscus along with the ACL and have the meniscus removed are six times more likely to have a graft rupture some time later. There is no common point at which graft rupture occurs. Sometimes it happens early on after the ACL repair. In other cases it can happen years later.

It doesn't look like luck has much to do with it. Stress and strain on the graft is more likely the culprit. Without the protective cartilage the graft repair is subject to higher forces and loads. The ligament starts to lengthen. Joint laxity develops -- in other words, the joint becomes looser over the years.

In the case of young athletes, doctors think rupture occurs because they are more active. This puts the reconstructed knee under greater stress more often.