Not to worry. The new double-bundle method is still in its early stages and may not be any better than the single-bundle repair your son had. With double-bundle repairs, the tendon graft is divided into two parts. The intent is to mimic the normal or natural anatomy, which has an anterior and posterior attachment of the same ligament.
Many surgeons say that the current single-bundle method gives good results when done well. In the hands of a good surgeon who does lots of these operations, the outcome is good to excellent.
The single-bundle repair is just as stable as the double-bundle. Most surgeons will tell you the typical athlete is more likely to injure the other knee than to reinjure the ACL repair.
Only highly trained specialists are even doing the double-bundle repair. Most orthopedic surgeons are using the single-bundled repair. So the jury is still out on the new double-bundle method.