Effects of modified trans-tibial versus trans-portal technique on stress patterns around the femoral tunnel in anatomical single-bundle ACL reconstruction with different knee flexion angles using finite element analysis

Abstract

Background It is unclear whether different anterior cruciate ligament (ACL) graft trajectories in the distal femur would have different effects on stress generated within the distal femur around the femoral tunnel during knee motion. Thus, the purpose of this study was to determine differences in stress patterns around the femoral tunnel created by trans-portal (TP) vs. modified trans-tibial (TT) technique in anatomical ACL reconstruction at different knee flexion angles. Methods Twelve male subjects’ right knees were scanned with a high-resolution computed tomography (CT) scanner (slice thickness: 1 mm) at four different knee flexion angles (0°, 45°, 90°, and 135°). Three-dimensional (3D) models of these four different flexion angles were created and manipulated with several modelling programs. For the TP group, the virtual femoral tunnelling procedure was performed in a 135° flexion model from the low far anteromedial (AM) portal. For the modified TT group, the same knee models were drilled through the modified TT technique at 90° of flexion separately. Virtual grafts under tension of 40 N were put into corresponding bone tunnel and fixed at the outer aperture of femoral tunnels to simulate the suspensory fixation, followed by fixation of the grafts at the middle of tibial tunnels in the 0° knee flexion models. Finally, the models were exported to a finite element analysis package and analysed using ABAQUS/Explicit code (ABAQUS, USA) to monitor the stress occurring at the node where stress distribution occurred most significantly in the femoral bone around the bone tunnel. Results In general, both groups showed a high stress distribution in bony structures around inner and outer orifices of the femoral tunnel. Mean maximal stresses occurring at the lateral femoral condyle around the inner orifice of the femoral tunnel in the TP group were found to be significantly greater than those in the modified TT group at all flexion angles except 90° of flexion. Mean maximal stresses monitored around the outer orifice of the femoral tunnel in the TP group were also significantly greater than those in the modified TT group at all flexion angles. Conclusions Different tunnelling technologies could yield different stress patterns in the lateral femoral condyle around the femoral tunnel. During knee motion, higher stresses were noticed in the TP group than in the modified TT group, especially around inner and outer orifices of the tunnel. Position of the tunnel after reconstruction with the TP technique can have a greater effect on the stress increase in the femur compared to that with the modified TT technique.

Elastin is responsible for the rigidity of the ligament under shear and rotational stress: a mathematical simulation study

“…In this study, we developed an original and simple mathematical simulation model of the collateral ligament based on two-photon images and previous studies. While conventional simulations often consider the ligament as a single sheet or bundle of collagen fibres [ 17 , 19 ], our model is unique in that elastin, which has its own mechanical properties, is placed between the collagen fibres. We compared this unique fibre model with a conventional sheet-like model and found that the distribution and magnitude of stress on the ligament, as well as the displacement of collagen fibres during tensile, shear, and rotational stresses, differed significantly between the two models.…”

“…Computer simulations can also be used to predict parameters for which the exact values are not known by comparing them with actual measurements. One pertaining problem is that many simulation studies consider the ligament to be a uniform collagen fibre bundle [ 15 – 17 ] or sheet [ 18 , 19 ], ignoring the mechanical properties of its other major components, elastin, and the interaction between collagen and elastin. Although the content and distribution of elastin have been studied at the molecular level and their unique mechanical properties have been tackled, their anatomical or physiological role in ligaments has not been fully understood.…”

Elastin is responsible for the rigidity of the ligament under shear and rotational stress: A mathematical simulation study

“…In this study, we have developed an original and simple mathematical simulation model of the collateral ligament based on two-photon images and previous literatures. While conventional simulations often consider the ligament as a single sheet or as a bundle of collagen bers [14,16], our model was unique in that elastin, which had its own mechanical property, was placed between the collagen bers. We compared this unique ber model with a conventional sheet-like model and found that the distribution and magnitude of stress on the ligament as well as displacement of the collagen bers during tensile, shear and rotational stresses differed signi cantly between two models.…”

“…On the other hand, elastin accounts for approximately 10% of the dry weight of the ECM and be thought to give the ligaments extensibility [11,12]. Most studies on the mechanical response of ligaments consider the ligament as a single uniform sheet [13,14] or focus only on collagen bers [15,16], ignoring the mechanical properties of the other major component, elastin, and the interaction between collagen and elastin. In addition, although the mechanical response of collagen bers at the micro level has been studied [17], the mechanical response between collagen and elastin at the submicron level has been little studied.…”

The healing effect of the all inside technique is superior to the traditional technique in the reconstruction of the anterior cruciate ligament

“… 22 This technique starts with arthroscopy and small incisions, preserving healthy tissue and using internal anchoring mechanisms like bioabsorbable implants, sutures, or fixation devices instead of external tunnels. 23 …”