Effect of knee flexion angle on length and orientation of posterolateral femoral tunnel drilled through anteromedial portal during anatomic double-bundle anterior cruciate ligament reconstruction.

PURPOSE

Our purpose was to evaluate the radiologic orientation and length of the posterolateral (PL) femoral tunnel when drilled through the anteromedial (AM) portal at 90 degrees, 110 degrees, and 130 degrees of flexion.

METHODS

In 9 fresh cadaveric knees the anterior cruciate ligament was excised and 2.4-mm guidewires were drilled through the center of the PL bundle footprint through an accessory AM portal. Pins were advanced, in a retrograde manner, until flush with the notch wall and left in place. Outcomes were measured by use of plain anteroposterior, lateral, and tunnel radiographs to determine tunnel orientation and clock position, and direct measurement was performed to determine the intraosseous length, the shortest distance to the posterior bone cortex, and the distance to the lateral collateral ligament attachment on the lateral aspect of the femoral condyle.

RESULTS

With regard to tunnel orientation, each increase in knee flexion angle resulted in a more horizontal tunnel on both the lateral and anteroposterior views. On the tunnel view, the PL guidewire became more vertical with knee flexion. The mean clock position was 9 o'clock (standard deviation [SD], 00:12). No significant difference in the intraosseous length of the guidewires was observed. According to our hypothesis, knee flexion influenced the PL tunnel characteristics. At 90 degrees of flexion, the guidewire may blow out the posterior cortex of the lateral femoral condyle.

CONCLUSIONS

A PL femoral tunnel drilled through the AM portal becomes more horizontal with bending of the knee during drilling. At 90 degrees, the tunnel is at risk of back wall blowout.