Influence of knee flexion angle on graft bending angle during anterior cruciate ligament reconstruction using the transportal technique

Abstract

This study aimed to examine change in the graft bending angle (GBA) according to various knee flexion angles in creating femoral tunnel by the transportal technique in ACL reconstruction, and to reveal knee flexion angle minimizing GBA while maintaining stable femoral tunnel characteristics. Patients who underwent ACL reconstruction using the transportal technique between January 2017 and December 2018 were retrospectively reviewed. Patients were classified into three groups according to knee flexion angle when creating femoral tunnel (group 1: < 120° (n = 19); group 2: 120-129° (n = 32); group 3: ≥ 130° (n = 33). GBA was measured on three-dimensional knee model reconstructed from postoperative computed tomography images. The length of the femoral tunnel and posterior wall blow-out were also checked. There was significant difference of GBA between the groups (group 1 = 112.1°; group 2 = 106.4°; group 3 = 101.4°, p < 0.001). The knee flexion angle in creating femoral tunnel was negatively correlated with GBA (r = - 0.733, p < 0.001). Five patients in group 1 had short femoral tunnel. GBA was influenced by knee flexion angle in creating femoral tunnel and got more acute as the knee flexion angle increased. Considering length and risk of wall blow-out in femoral tunnel, and GBA, knee flexion angle between 120 and 130° could be recommended as appropriate angle to create optimal femoral tunnel in ACL reconstruction using the transportal technique.

Figure 1

An accessory anteromedial portal placement and the knee position during the femoral tunnel creation. (A) An accessory anteromedial portal that could reach the ACL femoral footprint was created just above the medial meniscus, as far away as possible from the medial border of the patellar tendon. (B) The knee was flexed as much as possible in a figure-of-four position. The femoral tunnel was created by positioning the rigid mono-fluted reamer closest to the medial femoral condyle cartilage without damaging it. To protect the cartilage of the medial femoral condyle, a plastic cannula was used. A plastic cannula was pushed into the joint to cover the shaft of the reamer located within the joint during drilling.

Figure 2

Evaluation of the position of the femoral tunnel aperture by the quadrant method using three-dimensional knee model. The coordinates of the standard area of the ACL femoral footprint center were 27.5% ± 4.6% of the distance parallel to the Blumensaat line measured from the posterior border and 35.9% ± 9.2% of the distance perpendicular to the Blumensaat line measured from the Blumensaat line.

Figure 3

Evaluation of the position of the tibial aperture using axial plane of three-dimensional knee model. The coordinates of the standard area of the ACL tibial footprint center were 35.7% ± 3.3% of the anterior-to-posterior distance and 51.5% ± 3.4% of the medial-to-lateral distance on axial plane.

Figure 4

Evaluation of the graft bending angle with three-dimensional knee model. The graft bending angle is formed by the intra-articular graft vector ($\overrightarrow{G}$; the vector from the intra-articular femoral tunnel aperture to the intra-articular tibial tunnel aperture) and femoral tunnel vector ($\overrightarrow{\mathit{FT}}$; the vector from the intra-articular femoral tunnel aperture to the femoral tunnel outlet).

Figure 5

Pearson correlation analysis of graft bending angle and knee flexion angle in creating femoral tunnel. The knee flexion angle was negatively correlated with the graft bending angle measured at 0° of knee flexion (r = − 0.733, P < 0.001).