Factors affecting isometry of endoscopic anterior cruciate ligament reconstruction: the effect of guide offset and rotation.

Eight normal cadaveric knee specimens were used to evaluate the effects of femoral and tibial tunnel positions on length excursions of a single wire and bone-patellar tendon-bone graft as measured by an isometer. Femoral attachment sites were varied by using a commercially available femoral pin guide with either a 5.5- or 7.0-mm offset and by aiming with the guide oriented vertically (12:00 notch position) or rotating 45 degrees toward the lateral condyle (1:30 or 10:30 notch position depending on right or left knee). Tibial isometry was altered by testing the wire against the posterior tunnel wall or 5-mm anterior using a custom centering device. Isometry was measured from 0 degrees to 120 degrees for each position tested. A 7-mm offset guide rotated to the 12:00 position yielded the best single fiber and graft excursion patterns (P < .05). A 5.5-mm offset guide yielded inferior single fiber and graft excursion patterns. Single fiber and graft isometry were found to be similar, but not identical in endoscopic anterior cruciate ligament reconstruction. Centering the single fiber in the tibial tunnel had little effect on excursion patterns, showing that the more posterior tibial positions needed for endoscopic reconstruction are acceptable from an isometry standpoint.