Editorial Commentary: Tunnel Widening After Anterior Cruciate Ligament Reconstruction May Increase Laxity and Complicate Revision.

Tunnel widening (TW) after anterior cruciate ligament (ACL) reconstruction has been a research area of interest in ACL reconstruction. It has been demonstrated that femoral tunnels enlarge anteriorly and distally (ie, the direction where the mechanical traction force of the graft works) rather than concentrically after anatomic double-bundle ACL reconstruction using hamstring autografts. This finding suggests that the wall supporting the graft moves closer to the direction of the pull, leading to increased laxity of the knee joint due to TW. The causes of TW are presumed to be multifactorial, with both biological and mechanical features. Biological factors include osteolytic cytokines that enter the space between the graft and the bone through the synovial fluid. Mechanical factors include longitudinal graft motion by extracortical femoral fixation (known as the bungee effect), transverse graft motion (also called the windshield-wiper effect), improper graft placement, higher initial graft tension, accelerated rehabilitation, and so on. Although TW does not seem to affect short-term clinical outcomes from studies published to date, it is plausible to speculate that the expansion of the bone tunnel (ie, the edge where the graft tendon is fixed) would theoretically increase joint laxity to some extent, and it would be premature to conclude that TW has no effect on clinical outcomes relative to graft-tunnel micromotion. In addition, there is a general consensus that the presence of expanded tunnels often severely complicates revision ACL reconstruction. In ACL reconstruction using the hamstring tendon, it is necessary to take into account the possibility of a shift in the tunnel position when determining the location of the femoral tunnel.