Effect of tibial drill angles on bone tunnel aperture during anterior cruciate ligament reconstruction.

BACKGROUND

Anatomic reconstruction of the anterior cruciate ligament has received greater attention as patient outcome assessment has become increasingly sophisticated. A goal during anatomic reconstruction should be the creation of a tibial tunnel aperture that is similar in size and orientation to the native anterior cruciate ligament insertion. Aperture morphology depends primarily on three factors: (1) drill-bit diameter, (2) the angle at which the tunnel intersects the tibial plateau (drill-guide angle), and (3) the tibial tunnel orientation in the transverse plane (transverse drill angle). We evaluated the influence of the aforementioned factors on tibial bone-tunnel aperture size and orientation.

METHODS

With use of various drill-bit diameters at different drill-guide angles, tunnel aperture areas were calculated on the basis of an elliptical shape. The change in tunnel aperture orientation within the transverse plane (along the tibial plateau surface) was quantified by calculating the change in anteroposterior and mediolateral lengths of the aperture.

RESULTS

Use of a 9-mm drill-bit at a 45 degrees drill-guide angle created a 90-mm(2) bone-tunnel aperture area. Decreasing the drill-guide angle from 65 degrees to 30 degrees resulted in an increase in area of 81%. An aperture oriented 45 degrees relative to the orientation of the native insertion of the anterior cruciate ligament in the transverse plane fell short of the anatomic anteroposterior distance by 2.3 mm and exceeded the mediolateral distance by 1.4 mm on the basis of a 9-mm drill-bit at a drill-guide angle of 45 degrees.

CONCLUSIONS

During anterior cruciate ligament reconstruction, the drill-bit diameter, sagittal drill angle, and transverse drill angle can all affect tibial tunnel aperture size and orientation. An improperly sized and oriented tunnel aperture may increase the risk of damaging surrounding structures. An optimal combination of these parameters should be chosen during anatomic reconstruction of the anterior cruciate ligament.