For many years, surgeons have worked to improve and perfect reconstructive surgery for anterior cruciate ligament (ACL) ruptures. Athletes eager to get back to full sports participation were grateful for the opportunity to have the surgery and resume play. But now many years later, surgeons are asking some important questions.

ACL ruptures are surgically reconstructed by using a piece of graft material to replace the torn ligament. The graft is taken from the patient's own patellar or hamstring tendon. Studies show that the majority (75 to 80 per cent) of athletes return to their preinjury level of sports participation.

But what happens down the road for these individuals? How long does the ACL graft last? What are the chances of the graft rupturing? Why does it rupture? Knowing the risk factors might help patients prevent such an event. Does it really matter which location the graft comes from (patellar tendon or hamstrings)? And finally, what about the other knee? Does having an ACL rupture on one side increase the risk of an ACL tear on the other side?

These questions were addressed by an orthopedic surgeon and his staff from the North Sydney Orthopaedic and Sports Medicine Centre in Australia. They found some answers to these questions from telephone and written surveys their patients completed. There were 755 patients who had an ACL reconstruction and participated in the study.

No one was contacted until at least 15 years had passed from the time of their first ACL surgery. They were asked all sorts of questions about knee function, further injuries to either knee, additional knee surgeries, family history of ACL injuries, activity level, and satisfaction with results of surgery.

Specific information about each patient was collected from their medical records (e.g., age, gender, leg affected, type of graft used, date of injury and date of surgery). They were able to find out all sorts of interesting information about this group of patients.

For example, rupture of the ACL on the other side was less than one per cent per year and most likely to occur between year one and year four after the primary (first) ACL surgery. Patients who had patellar tendon grafts were twice as likely to have an ACL rupture in the opposite leg compared with those patients who had the hamstring graft. The type of graft did not seem to affect the primary ACL repair -- ruptures occurred equally between the patellar tendon group and the hamstring group.

ACL grafts survived intact for 97 per cent of the entire group in the first two years. But the risk of rupture increased as time went by. Rupture of the surgical graft affected 11 per cent of the group. When rupture did occur, it was most likely to happen in the first year after the primary surgery. Men and women experienced graft rupture equally.

There was one final bit of information gleaned from this study. Patients with a family history of ACL rupture had double the risk of both ACL graft rupture and rupture of the ACL on the other side.

This is the first study to take a serious look at the risk and risk factors for ACL rupture in the opposite knee after injury and reconstructive surgery to the primary (first) knee affected. Injury of the ACL in the second knee occurs more often than anyone previously suspected.

All the risk factors probably haven't been identified yet. But graft type (patellar tendon) and age (younger patients) were two of the main risk factors. Younger age is linked with higher activity level and therefore increased risk of injury. Two other possible risk factors that have not been proven yet are: 1) graft size on the surgical side is larger than ACL on the opposite side creating some differences in tension and 2) greater load on the opposite leg as that leg works harder to protect the injured leg.

How will surgeons use this information? First, patients can be screened more carefully for risks that might contribute to rerupture of the surgical graft and ACL rupture on the other side. Second, rehab can be recommended (especially for physically active patients) that addresses both sides to minimize the risk of more injuries. One rehab method already available and proven effective is the use of plyometric exercises.

This type of exercise training involves fast, powerful movements. Athletes use it to improve the functions of the nervous system, generally for the purpose of improving performance in sports.

But anyone can use these techniques -- being a sports athlete isn't a requirement. During plyometric movements the leg muscles are loaded and then contracted in rapid sequence. Plyometric training involves practicing these movements to toughen tissues and train nerve cells with the goal of getting the muscles to contract in a specific pattern in the shortest amount of time.

Surgeons can also use this information to counsel patients what to expect, especially regarding the risk of rerupture of the ACL graft or first-time rupture of the ACL on the opposite side. Identifying and minimizing all modifiable risk factors requires both surgeon and patient participation and cooperation in the process.

Reference: Henry E. Bourke, FRCS (Tr&Orth), et al. Survival of the Anterior Cruciate Ligament Graft and the Contralateral ACL at a Minimum of 15 Years. In The American Journal of Sports Medicine. September 2012. Vol. 40. No. 9. Pp. 1985-1992.