In Vivo Analysis of Dynamic Graft Bending Angle in Anterior Cruciate Ligament–Reconstructed Knees During Downward Running and Level Walking: Comparison of Flexible and Rigid Drills for Transportal Technique

Abstract

Purpose To determine in vivo dynamic graft bending angle (GBA) in anterior cruciate ligament (ACL) reconstructed knees, correlate the angle to tunnel positions and tunnel widening, and evaluate the effects of two femoral tunnel drilling techniques on GBA. Methods Patients with an isolated ACL injury undergoing reconstruction were included from 2011 to 2012. Trans-portal techniques were used to create femoral tunnels. Tunnel locations were determined using 3D-CT. Tibio-femoral kinematics during treadmill walking and running were assessed using dynamic stereo X-ray analysis 6 months and 2 years postoperatively. The GBA was calculated from the 3D angle between the graft and femoral tunnel vectors at each motion frame. Cross-sectional area of femoral tunnels were measured at 6 months and compared to initial size to assess tunnel widening. Results A total of 54 patients were included. Use of flexible drills resulted in significantly higher GBA during walking (80.6° ± 7.8°; p<0.001) and running (80.5° ± 9.0°; p=0.025) than rigid drills (walking: 67.5° ± 9.3°, running: 74.1° ± 9.6°). It led to greater tunnel widening of 113.9±17.6 %, compared with rigid drills of 97.7±17.5 % (p=0.003). Femoral and tibial apertures were located in similar anatomic positions in both groups, but femoral tunnel exits were located more anteriorly (p<0.001) in the flexible drill group. Higher GBA was highly correlated with anterior location of femoral exits (r=0.63, p<0.001) and moderately correlated with greater tunnel widening (r=0.48, p<0.001). Conclusions High GBA was identified during dynamic activities after anatomic ACL reconstruction using a trans-portal femoral tunnel drilling technique. The GBA was greater when flexible drills were used. The high bending angle resulted from more anterior location of femoral tunnel exits, and correlated with early bone tunnel widening at 6 months. These results suggest that high GBA may increase stress on the bone-graft interface and contribute to greater tunnel widening after anatomic ACL reconstruction, although clinical impact should be further investigated. Level of Evidence Level III, retrospective comparative study

Influence of Graft Bending Angle on Graft Maturation, the Femoral Tunnel, and Functional Outcomes by 12 Months After Anterior Cruciate Ligament Reconstruction

“…First, the femoral tunnel was drilled with the knee at maximal flexion in our cohort, which might have resulted in a more posterior femoral tunnel exit. 28,29 Because it has been reported that a more posterior femoral tunnel exit correlates with a smaller GBA, our surgical technique might have contributed to low GBA values. 29 Second, the GBA and bone tunnel were measured on 3D MRI based on the graft axis in this study.…”

“…Severe femoral tunnel widening may result in impairment of graft incorporation, joint laxity, and complications in revision surgery. 1,23 Tashiro et al 28 used a quadriceps tendon autograft with a bone block in ACLR, and they demonstrated that a higher GBA moderately correlated with greater tunnel widening. Segawa et al 22 reported that a higher GBA may increase mechanical stress on the anterior margin of the femoral tunnel.…”

“…The graft bending angle (GBA), the angle between the femoral bone tunnel and the line connecting the femoral and tibial tunnel apertures, 20,24 has been proven to influence stress within the graft, and it might be an important factor in graft healing within the joint and bone tunnel. 18,28,33 A higher GBA could lead to tunnel widening. 21 It has also been found to correlate significantly with a higher graft signal intensity (SI) on magnetic resonance imaging (MRI), which might indicate poorer ACL graft healing.…”

A Hybrid Transtibial Technique Combines the Advantages of Anteromedial Portal and Transtibial Approaches: A Prospective Randomized Controlled Trial

“…It has been previously shown that the magnitude of the graft bending angle seen with AM portal tunnels results in a 2- to 3-fold increase in graft strain at the femoral tunnel aperture, producing increased graft signaling on postoperative magnetic resonance imaging. 12,21,34,35…”

“…This makes graft passage more tedious, increases graft forces at the tunnel aperture, and may negatively affect graft healing. 5,12,34,35…”