I’m retired now from teaching with enough time on my hands to start worrying about all kinds of things. One thing that came to mind is my ACL repair of 10 years ago. Is this like those knee replacements that wear out after 10 to 15 years? Am I going to need another ACL surgery when (if?) this one gives out? What can you tell me so I can find something else to worry about? (Just kidding).

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 patients return to their preinjury level of activity.

But like you, many patients wonder what will happen down the road after this surgery? How long will 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. And what about the other knee? Does having an ACL rupture on one side increase the risk of an ACL tear on the other side?

Studies show that the risk of rupture of the ACL on the other side is less than one per cent per year. If it’s going to happen, it will most likely occur between year one and year four after the primary (first) ACL surgery. You are well past that now.

Patients who have patellar tendon grafts may be more likely to have an ACL rupture in the opposite leg compared with those patients who have the hamstring graft. ACL grafts survive intact in the first two years for 90 per cent or more of patients studied.

But the risk of rupture increases as time goes by. Rupture of the surgical graft affects about 10 per cent of patients studied. When rupture does occur, it will most likely to happen in the first year after the primary surgery. Again, you have moved well past this bench mark.

All the risk factors for rerupture of the injured side and rupture of the opposite side probably haven’t been identified yet. But graft type (patellar tendon) and age (younger patients) may be two of the main risk factors.

Younger age is linked with higher activity level and therefore increased risk of injury. Unless you are an extremely active retiree, this doesn’t describe you either. 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) there is greater load placed on the opposite leg as that leg works harder to protect the injured leg.

If you are experiencing any symptoms that would make you think either knee is unstable or changing in function or strength, then see your surgeon for a follow-up evaluation. You may want to do this anyway to relieve your mind of any further worry.