A double-bundle graft in ACL surgery uses two bundles of graft material instead of one, to try to mimic the normal ligament.
The natural ACL is composed of two ligament bundles - an anteromedial bundle and a posterolateral bundle. The double-bundle reconstruction uses two individual grafts to try to reconstruct the original anatomy.
Double-bundle reconstruction is more challenging to perform, and from the patient's perspective there are two additional bone tunnels and one additional incision (skin cut).