The Femoral Tunnel Drilling Angle at 45° Coronal and 45° Sagittal Provided the Lowest Peak Stress and Strain on the Bone Tunnels and Anterior Cruciate Ligament Graft

Abstract

Purpose: The aims of this study were to 1) investigate the effects of femoral drilling angle in coronal and sagittal planes on the stress and strain distribution around the femoral and tibial tunnel entrance and the stress distribution on the graft, following anterior cruciate ligament reconstruction (ACLR), 2) identify the optimal femoral drilling angle to reduce the risk of the tunnel enlargement and graft failure.Methods: A validated three-dimensional (3D) finite element model of a healthy right cadaveric knee was used to simulate an anatomic ACLR with the anteromedial (AM) portal technique. Combined loading of 103.0 N anterior tibial load, 7.5 Nm internal rotation moment, and 6.9 Nm valgus moment during normal human walking at joint flexion of 20° was applied to the ACLR knee models using different tunnel angles (30°/45°/60° and 45°/60° in the coronal and sagittal planes, respectively). The distribution of von Mises stress and strain around the tunnel entrances and the graft was calculated and compared among the different finite element ACLR models with varying femoral drilling angles.Results: With an increasing coronal obliquity drilling angle (30° to 60°), the peak stress and maximum strain on the femoral and tibial tunnel decreased from 30° to 45° and increased from 45° to 60°, respectively. With an increasing sagittal obliquity drilling angle (45° to 60°), the peak stress and the maximum strain on the bone tunnels increased. The lowest peak stress and maximum strain at the ACL tunnels were observed at 45° coronal/45° sagittal drilling angle (7.5 MPa and 7,568.3 μ-strain at the femoral tunnel entrance, and 4.0 MPa and 4,128.7 μ-strain at the tibial tunnel entrance). The lowest peak stress on the ACL graft occurred at 45° coronal/45° sagittal (27.8 MPa) drilling angle.Conclusions: The femoral tunnel drilling angle could affect both the stress and strain distribution on the femoral tunnel, tibial tunnel, and graft. A femoral tunnel drilling angle of 45° coronal/ 45° sagittal demonstrated the lowest peak stress, maximum strain on the femoral and tibial tunnel entrance, and the lowest peak stress on the ACL graft.

Central femoral tunnel placement can reduce stress and strain around bone tunnels and graft more than anteromedial femoral tunnel in anterior cruciate ligament reconstruction

“…The AM femoral tunnel was placed through the center of the native AM footprint 6,18 . In contrast, the central femoral tunnel was placed through the central anatomical footprint between AM/PL footprints 6,18,19 . The tibial tunnel was drilled through the center of the ACL tibial footprint.…”

“…The tibial tunnel was drilled through the center of the ACL tibial footprint. The femoral tunnel was drilled through the AM portal technique at a coronal obliquity angle of 45° and a sagittal obliquity angle of 45° 19–21 . The tibial tunnel was drilled at a tibial angle of 20° in the coronal plane and 60° in the sagittal plane 17,19,22 .…”

“…A combined loading condition was applied to the ACLR model at 20° of joint flexion: 103 N anterior tibial load (15% body weight [BW]), 7.5 Nm internal rotation moment (1.1% BW), and 6.9 Nm valgus moment (1% BW) 14,16,19,29 . This combined loading represented the worst‐case condition for the ACL graft during human walking 29 .…”

“…This combined loading represented the worst‐case condition for the ACL graft during human walking 29 . The peak von Mises stress and maximum principal strain around the entrances of the bone tunnel and on the graft were determined and compared between the AM femoral tunnel placement and the central femoral tunnel placement according to the method of a previous study 19 …”

“…6,18 In contrast, the central femoral tunnel was placed through the central anatomical footprint between AM/PL footprints. 6,18,19 The tibial tunnel was drilled through the center of the ACL tibial footprint. The femoral tunnel was drilled through the AM portal technique at a coronal obliquity angle of 45 and a sagittal obliquity angle of 45 .…”