Principles for placing the tibial tunnel and avoiding roof impingement during reconstruction of a torn anterior cruciate ligament.

Reconstruction of a form anterior cruciate ligament (ACL) cannot be successful without a properly placed tibial tunnel. Preventable complications such as anterior knee pain, effusions, extension loss, and recurrent instability can occur when the tibial tunnel is improperly placed and the roof and notchplasty are insufficient. This article reviews the principles for anatomic placement of the tibial tunnel so that complications associated with impingement of the ACL graft on the intercondylar roof can be prevented. Five factors that contribute to roof impingement are discussed, including differences in the size and shape of the ACL and the graft, variability in knee extension and roof angle between patients, inability to view the contact between the intercondylar roof and the graft, accentuation of roof impingement from anterior tibial translation caused by quadriceps contraction, and the use of tibial guides that rely on soft-tissue landmarks. A surgical technique is presented which consistently places the tibial tunnel in the pathway of the normal ACL (i.e., anatomic placement) and avoids roof impingement. The indications and need for roof- and wallplasty are discussed.