The "N + 7 rule" for tibial tunnel placement in endoscopic anterior cruciate ligament reconstruction.

Tibial tunnel placement during endoscopic anterior cruciate ligament (ACL) reconstruction has received increased emphasis in the recent literature. Appropriate tunnel length is a critical technical consideration. A tunnel that is too short results in graft extrusion, necessitating supplemental fixation techniques. A tunnel that is too long may make distal fixation and femoral tunnel placement difficult. A simple rule is proposed that allows for correct tunnel length and allows placement of the bone plug consistently within the tibial tunnel, allowing interference screw fixation.