The orientation of the ALL femoral tunnel to minimize collision with the ACL tunnel depends on the need or not of far-cortex drilling

Abstract

Purpose To (1) evaluate the optimal drill orientation of the anterolateral ligament (ALL) femoral tunnel to minimize collision with the anterior cruciate ligament (ACL) femoral tunnel during anatomical ACL reconstruction according to the need for far-cortex drilling and (2) investigate the geometric factors that afect tunnel collision secondary to drill orientation of the ALL femoral tunnel. Methods A three-dimensional femoral model of patients who underwent anatomical single-bundle ACL reconstruction between 2015 and 2016 was constructed, and the geometric factors were evaluated. Virtual ALL femoral tunnels were created to simulate 45 drilling conditions. For each condition, whether the virtual ALL femoral tunnel and its trajectory violated the femoral cortex and the minimum distance between tunnels was investigated. Results Thirty-nine subjects were included. Overall violation rates of the femoral cortex by the ALL tunnels and its trajectories were 11.1% (195 of 1755 conditions) and 40.7% (714 of 1755 conditions), respectively. A drilling angle of axial 0° and coronal − 40° showed the longest minimum distance between tunnels without femoral cortex violation by the ALL tunnel (6.3 ± 4.0 mm; collision rate 2.6% [1 of 39 subjects]). With simultaneous consideration of the ALL tunnel's trajectory representing far-cortex drilling, a drill angle of axial 40° and coronal 10° showed the longest minimum distance between tunnels without femoral cortex violation (0.6 ± 3.9 mm; collision rate 38.5% [15 of 39 subjects]). For surgical techniques requiring far-cortex drilling, regression analyses were performed on geometric factors that could afect tunnel collision, which revealed that the sagittal inclination angle of the ACL and the distance between the ACL femoral tunnel's outlet and ALL's femoral attachment were associated with tunnel collision. ConclusionThe optimal drill orientations of the ALL femoral tunnel to minimize collision with the ACL femoral tunnel were axial 0° and coronal − 40° for surgical techniques not requiring far-cortex drilling and axial 40° and coronal 10° for techniques requiring far-cortex drilling. For techniques requiring far-cortex drilling, additional adjustment for orientation of the ACL femoral tunnel is required to reduce the risk of tunnel collision. Therefore, an individualized surgical strategy should be applied according to the graft ixation method of the ALL femoral tunnel.

Incidence of Convergence Between Distally and Anteriorly Oriented ALL Femoral Tunnels and ACL Femoral Tunnels in Combined ACL and ALL Reconstruction: 3-Dimensional Computed Tomography Analysis of 227 Patients

“…Many studies have shown a high percentage of tunnel convergence in ACL and ALL reconstruction and recommended that the ALL tunnel be oriented at specific angles to avoid convergence. 9,11,12,19 In our study, tunnel convergence could be effectively avoided if the ALL tunnel were placed at anterior and distal angles .24°. This result was similar to that in the study by Moon et al 12 for procedures not requiring far cortex drilling.…”

“…9,11,12,19 In our study, tunnel convergence could be effectively avoided if the ALL tunnel were placed at anterior and distal angles .24°. This result was similar to that in the study by Moon et al 12 for procedures not requiring far cortex drilling. In our study, there was no significant difference in the ACL femoral tunnel between groups.…”

“…Most studies did not even consider distal and anterior angles because all of these studies involved far cortex drilling. 12,18,19,27 When far cortex drilling is eliminated, guiding the drill distally and anteriorly becomes an option because one does not have to worry about violating important intra-articular structures. The current study showed that short drilling of the lateral femoral cortex and using appropriate fixation devices can provide stable fixation of the ALL, minimize convergence with the ACL tunnel at certain angles, and decrease the risk of any far cortex violation.…”

“…11 With this in mind, various studies have been conducted to minimize the risk of tunnel convergence. 9,12,17,19,20,27 Some studies recommended specific angles and orientations of the tunnel in different planes. 9,12 Other studies reported that tunnels must be drilled according to the fixation method of the ALL femoral tunnel.…”

“…9,12,17,19,20,27 Some studies recommended specific angles and orientations of the tunnel in different planes. 9,12 Other studies reported that tunnels must be drilled according to the fixation method of the ALL femoral tunnel. 12,27 Although such previous studies generally agree that tunnel convergence should be avoided, there is no consensus on how the ALL tunnel should be oriented to minimize the risk of tunnel convergence.…”