Increased ACL Direct Insertion Coverage Provided More Positive Biomechanical Effects on Graft and Bone Tunnel During Knee Flexion: a Simulation Study

Purpose: Flattened femoral tunnels were recently applied in anatomical single-bundle anterior cruciate ligament (ACL) reconstruction. Little is known about the biomechanical effect of such changes during knee flexion. The aim of the present simulation study was to assess the effect of altered ACL direct insertion coverage on the biomechanics of the graft and bone tunnel.

Methods: Five finite element (FE) models, including a round femoral tunnel and four progressively flattened rounded rectangular femoral tunnels, were established to represent the ACL reconstructions. In vivo knee kinematics data obtained from the validated dual fluoroscopic imaging techniques controlled the FE models to simulate lunge motions. The maximal principal stress of the graft and the volume of equivalent strain within 1000-3000 microstrain (V) of the cancellous bone were subsequently calculated at 0°, 30°, 60° and 90° of knee flexion.

Results: A lower stress state on the graft and a more beneficial strain state on the cancellous bone were observed when the femoral tunnel better covered the ACL direct insertion. The average maximal principal stress of each model were 3.93 ± 0.60 MPa, 3.82 ± 0.54 MPa, 3.43 ± 0.44 MPa, 3.45 ± 0.44 MPa and 3.05 ± 0.43 MPa, respectively. The average V of the cancellous bone of each model were 179.06 ± 89.62 mm, 221.40 ± 129.83 mm, 247.57 ± 157.78 mm, 282.74 ± 178.51 mm and 295.71 ± 162.59 mm, respectively. Both the stress and strain values exhibited two peaks during the flexion simulation. The highest value occurred at 30° of flexion, and the second highest value occurred at 90° of flexion.

Conclusions: Increased ACL direct insertion coverage provided more positive biomechanical effects after anatomical single-bundle ACL reconstruction during knee flexion.