I’m going to have surgery to reconstruct a torn ACL in my left knee. The physician’s assistant who explained the surgery to me said something about two bundles that will be repaired. What are these bundles?

Studies have shown that the anterior cruciate ligament isn’t a single, individual bundle of tissue fibers. Instead, it’s clear that there are two separate bundles or segments of ligament.

The anteromedial bundle is the front and inside portion of the ligament. The posterolateral segment is the back and outside section. Together, these two bundles help provide the stability needed by the joint.

When the ACL is torn or deficient for any reason, the tibia (lower leg bone) slides forward too much. This laxity or looseness can cause the leg to give out from underneath the person. Surgical repair of the ACL may be needed.

New research shows that both bundles may need to be reconstructed separately. The anteromedial portion helps prevent too much forward translation or glide of the tibia. The posterolateral bundle is important in reducing the rotation of the tibia during knee motion.

Improved technology and computer-assisted surgery has made it possible to identify both bundles. Surgical technique is changing from a single-bundle reconstruction to a double-bundle repair.