Anterior cruciate ligament femoral-tunnel drilling through an anteromedial portal: 3-dimensional plane drilling angle affects tunnel length relative to notchplasty.

Background: Notchplasty is a surgical technique often performed during anterior cruciate ligament reconstruction (ACLR) with widening of the intercondylar notch of the lateral distal femur to avoid graft impingement. The purpose of this study was to correlate femoral-tunnel length with 3-dimensional (3D) drilling angle through the anteromedial (AM) portal with and without notchplasty.

Materials and methods: Computer data were collected from an anatomical study using 16 cadaveric knees. The anterior cruciate ligament (ACL) femoral insertion was dissected and outlined for gross anatomical observation. The dissected cadaveric knees were scanned by computed tomography (CT). Three-dimensional measurements were calculated using software (Geomagic, Inc., Research Triangle Park, NC, USA) and included the center of the ACL footprint and the size of the ACL femoral footprint. The femoral-tunnel aperture centers were measured in the anatomical posterior-to-anterior and proximal-to-distal directions using Bernard's quadrant method. The ACL tunnel was created 3-demensionally in the anatomical center of femoral foot print of ACL using software (SolidWorks®, Corp., Waltham, MA, USA). The 8-mm cylinder shaped ACL tunnel was rested upon the anatomical center of the ACL footprint and placed in three different positions: the coronal plane, the sagittal plane, and the axial plane. Finally, the effect of notchplasty on the femoral-tunnel length and center of the ACL footprint were measured. All the above-mentioned studies performed ACLR using the AM portal.

Results: The length of the femoral tunnels produced using the low coronal and high axial angles with 5-mm notchplasty became significantly shorter as the femoral starting position became more horizontal. The result was 30.38 ± 2.11 mm on average at 20° in the coronal plane/70° in the axial plane/45° in the sagittal plane and 31.26 ± 2.08 mm at 30° in the coronal plane/60° in the axial plane/45° in the sagittal plane, respectively, comparing the standard technique of 45° in the coronal/45° in the axial/45° in the sagittal plane of 32.98 ± 3.04 mm (P < 0.001). The tunnels made using the high coronal and low axial angles with notchplasty became longer than those made using the standard technique: 40.31 ± 3.36 mm at 60° in the coronal plane/30° in the axial plane/45° in the sagittal plane and 50.46 ± 3.13 mm at 75° in the coronal plane/15° in the axial plane/45° in the sagittal plane (P < 0.001).

Conclusions: Our results show that excessive notchplasty causes the femoral tunnel to be located in the non-anatomical center of the ACL footprint and reduces the femoral-tunnel length. Therefore, care should be taken to avoid excessive notchplasty when performing this operation.